Parus major) pedigree with simulations, we assess how heritability estimates derived from social pedigrees change depending on the mode of the relationship between EPP and the focal trait. We show that the magnitude of the underestimation is typically small (<15%). Hence, our analyses suggest that quantitative genetic inference from pedigrees derived from observations of social relationships is relatively robust; our approach also provides a widely applicable method for assessing the consequences of nonrandom EPP.Quantitative genetic analysis is often fundamental for understanding evolutionary processes in wild populations. Avian populations provide a model system due to the relative ease of inferring relatedness among individuals through observation. However, extra‐pair paternity (EPP) creates erroneous links within the social pedigree. Previous work has suggested this causes minor underestimation of heritability if paternal misassignment is random and hence not influenced by the trait being studied. Nevertheless, much literature suggests numerous traits are associated with EPP and the accuracy of heritability estimates for such traits remains unexplored. We show analytically how nonrandom pedigree errors can influence heritability estimates. Then, combining empirical data from a large great tit ( Estimating the heritability of traits in wild populations is fundamental in determining responses to selection, as well as understanding patterns of genetic variation  population for which both a detailed social pedigree (gained through observations) and genetic pedigree  was available , of paternity in multiple ways. Therefore, first, we analytically derive how the trait values of the social and genetic fathers may influence heritability estimates from father–offspring regression. Second, we explore how animal model estimates of heritability are influenced by the degree, and mode, of nonrandom EPP within authentic populations using a permutation approach. As wild populations may differ in pedigree structure from both animal breeding designs and simple simulated pedigrees, which may also influence heritability estimation  can be used in assessing heritability of traits that may correlate with paternal misassignment in wild pedigrees.z is the trait value of the social father and o the trait value of the offspring. Under the assumptions that (1) the social father's trait does not have a paternal effect; (2) there is no genetic correlation between the trait and female preference; and (3) there is no inbreeding, then  cov = cov /2, where a is the breeding value of the offspring's genetic father. If we assume that mating behavior is determined directly by the studied phenotype, thenz' is the phenotype of the genetic father. Denoting EPP events as δ=1 (δ=0 otherwise ), where δ is also a random variable:e is the phenotype of the extra‐pair male (EPM), which is not defined when δ=0. It can be shown (see Supporting Information) thatδ¯ is the mean EPP rate, γ is the ratio of the variance in phenotype of cuckolded males compared to all males, βe|z is the regression of EPM phenotype on social father phenotype, βδ|z is the regression of being cuckolded on the social father phenotype, and Δ the average difference between the phenotypes of EPMs and the social fathers they cuckold. Perhaps surprisingly, equation βe|z=0), nor a relationship between social father phenotype and the probability of being cuckolded (βδ|z=0) and so necessarily γ=1. This result has been used previously to estimate δ¯ before the advent of cheap molecular markers  when patterns and rates of EPP are associated with the cuckolded male's phenotype. This can happen through two broad, but interacting, mechanisms. First, the phenotypes of EPMs and those they cuckold could be correlated, with a positive correlation (βe|z>0) reducing bias and a negative correlation (βe|z<0) increasing bias. However, a lower bound onβe|z is −1 if the variances in trait value for all males, EPMs, and cuckolded males are approximately equal, and so heritability estimates from animal models are unlikely to be biased downwards by more than twice the EPP rate, and most likely substantially less.However, the bias is not simply determined by the EPP rate (βδ|z<0) and the phenotype of EPM is larger than the average (Δ>0) or vice versa. It should be noted that even if EPP is independent of EPM phenotype these two quantities will have different signs: if social fathers with low trait values get cuckolded (βδ|z<0) then by necessity EPMs (which are drawn randomly from the population) will have larger trait values (Δ>0). However, if EPP also depends on EPM phenotype then this is not necessarily the case: as an extreme example, imagine two types of male with phenotypes 0 and 1 and that males with phenotype 1 neither gain nor lose EPP, but males with phenotype 0 lose all their paternity (to each other). Under this example βδ|v=−1, yet Δ=0. Under these conditions E[h2^]=h2 (because γ=0) and there is no bias; this makes intuitive sense because the social father of every offspring has the same phenotype as the genetic father. In contrast, if males with phenotype 0 lost all their paternity to males with phenotype 1 then Δ=1 and E[h2^]=0 generating large biases.A second mechanism is if the probability of being cuckolded depends on the social father's phenotype. Here, bias will increase when the probability of being cuckolded decreases with trait vale  of 9193 Single‐nucleotide polymorphism (SNP) . Following quality control, a linkage map of the great tit genome was constructed, with 4701 SNPs mapped to autosomes . For computational reasons, a set of 1700 of the mapped SNPs were chosen for parentage analysis by selecting a third of evenly spaced SNPs on each chromosome to reduce interdependence. CERVUS 3.0  was employed to confirm social paternal pedigree links and identify previously unknown genetic links. For each offspring, the pool of candidate fathers included all genotyped males at least one year older than itself. Using 10,000 simulated mating events, paternity was assigned to the male with the highest paternity likelihood if they were assigned with high confidence (>99%) in CERVUS.As this study was aimed at examining the possible effects of misassigned paternities, rather than data completeness :m and n) observed that year. To incorporate the likelihood that there are spatial constraints on the occurrence of EPP, dij was defined as the distance between the potential EPM and the social father, and λ as the rate of decline of the probability of EPP with distance. We investigated five EPP scenarios with different functional forms for f, where z is trait value:i, that is, EPM trait values increase the probability of gaining EPP: f=zi.The trait of male j, that is, social father trait values decrease the probability of being cuckolded: f=−zj.The trait of male f=zi−zj.A combination of (i) and (ii): f=|zi−zj|.The absolute difference in trait values between the EPM and social father increases the probability of EPY within this brood: f=−|zi−zj|.The absolute difference in trait values between the EPM and social father decreases the probability of EPY within this brood: We used simulation techniques to assess how the estimates of traits with heritabilities of 10, 30, 50, and 70% (a range spanning estimates often made for traits in wild populations) were influenced when linked to EPP through the five different mating scenarios. All analyses were run in R  of one so that β can be roughly interpreted as a standardized selection gradient (note that β must be multiplied by two in scenario [iii] to get the standardized selection gradient).Under each scenario, β was set as either 0, 0.1, 0.2, 0.4, 0.8, or 1.6; these values range from no association between the trait and EPP (or “zero selection”) to strengths of association (or “selection”) well above the range typically encountered in wild populations.βe|z,βδ|z, and Δ identified as important in the analytical model (eq. A number of extra‐pair (EP) events  were then drawn from the distribution defined by equation odel eq. . FurtherVA) and residual variance (VR) , EPP scenarios (n = 5), and different strength of these scenarios (n = 6), 100 simulated pedigrees were generated and analyzed.For the social, observed genetic, and simulated genetic pedigrees, the additive genetic variance , our genetic pedigrees simulated with no association between the male trait and EPP  did not differ from the observed genetic pedigree in measurements of pedigree structure that could be influenced by such techniques Fig. . This enβe|z) becomes more negative in this scenario, yet, when males cuckold others most similar from themselves (scenario [v]), βe|z increases  is only generated when this was directly simulated  song  is very close to the average EPP rate of socially monogamous bird species (∼11%, Griffith et al. In conclusion, although pedigree errors in wild populations only result in minor underestimation of heritability of particular traits (Keller et al. Supplementary InformationClick here for additional data file.


However, the small and negative tunnelling magnetoresistance that we find is attributed to predominant tunnelling from the lower moment Mn–Ge termination layers that are oppositely magnetized to the higher moment Mn–Mn layers. The net spin polarization of the current reflects the different proportions of the two distinct termination layers and their associated tunnelling matrix elements that result from inevitable atomic scale roughness. We show that by engineering the spin polarization of the two termination layers to be of the same sign, even though these layers are oppositely magnetized, high-tunnelling magnetoresistance is possible.Although high-tunnelling spin polarization has been observed in soft, ferromagnetic, and predicted for hard, ferrimagnetic Heusler materials, there has been no experimental observation to date of high-tunnelling magnetoresistance in the latter. Here we report the preparation of highly textured, polycrystalline Mn Heusler alloy thin films with a distorted tetragonal structure have potential spintronics applications given their bulk perpendicular magnetic anisotropy. Here, the authors demonstrate large perpendicular magnetic anisotropy in Mn3Ge thin films accompanied by negative tunnelling magnetoresistance. Key to the successful development of magnetic random access memory (MRAM), one of the most promising emerging non-volatile memory technologies today, are new magnetic materials for the magnetic tunnel junction (MTJ) memory elements that have sufficient stability against thermal fluctuations to sustain deeply scaled devices. The most promising magnetic materials to date are considered to be magnetic alloys formed from Co, Fe and B, in conjunction with MgO001) tunnel barriers tunnel b23xGa ref.  and Mn3G3Ge ref. .3(001) or MgO(001) using seed layers formed from a variety of materials but preferably Cr or Pt /SiO2) using underlayers formed from TaN/IrMn3 (TI). The magnetic properties of these films are comparable or superior to films that we have grown under similar conditions on single crystal MgO(001) substrates using epitaxial Cr(001) underlayers. Very high magnetic anisotropy fields exceeding 7T are found. However, the tunnelling magnetoresistance (TMR) is negative and much smaller than theoretical predictions for tunnel junction devices formed with MgO tunnel barriers. We attribute this to predominant tunnelling from the lower moment Mn–Ge termination layers that are oppositely magnetized to the higher moment Mn–Mn layers. The net spin polarization of the current reflects the different proportions of the two distinct termination layers and their associated tunnelling matrix elements at the tunnel barrier interface, that result from inevitable atomic scale roughness. We have confirmed that a second perpendicularly magnetized Heusler compound, Mn2CuSb, which we identified by computational materials discovery methods, similarly displays small TMR, but that the sign of the spin polarization of each of the termination layers is opposite to that of their magnetization, in contrast to Mn3Ge. Therefore, the low TMR that we have found in Mn3Ge and Mn2CuSb, which we attribute to termination layer compensation, is not an inherent property of ferrimagnetic Heuslers. The spin polarization of the two termination layers can be engineered to be of the same sign even though these layers are oppositely magnetized, therefore providing a path to low magnetization electrodes with high TMR for high density spin transfer torque MRAM applications.Here we show that thin films of ferrimagnetic Mn3Ge films were grown by either ion-beam deposition or d.c.-magnetron sputtering in an ultra-high vacuum chamber with a base pressure of ∼4 × 10−10 torr on Si(001) substrates covered with 250 Å of amorphous SiO2. We find that seed layers formed from bilayers of TaN/IrMn3 that are first deposited on the SiO2 induce (001) textured Mn3Ge films that are tetragonally distorted. IrMn3 is known to have a L12 structure that is cubic, and which matches one of the sublattices of the structure that Mn3Ge is known to form. Moreover, the lattice mismatch between IrMn3 and Mn3Ge is <1%  out-of-plane orientation when grown directly on amorphous SiO2 surface  roughness of the Mn3Ge film, rr.m.s., measured using atomic force microscopy, increases significantly when the growth temperature (TG) exceeds modest temperatures of just ∼200 °C, but higher growth temperatures are needed to sustain the Heusler structure, as measured from X-ray diffraction  with high PMA. During the annealing step of Mn3Ge films, there is a substantial inter-diffusion between IrMn3 and Mn3Ge layers . We note that a single TaN underlayer gives much poorer quality Mn3Ge layers.The structural and magnetic properties of the Mnfraction . Thus, we layers , which curements . Thus, t3Ge films with varying thickness grown on amorphous substrates using the three-step process and on a crystalline MgO(001) substrate with a Cr seed layer (MC). Excellent PMA is observed in all cases but the highest coercive and anisotropy fields are found for structures grown on the TIT underlayer. Coercive fields of 6T and anisotropy fields exceeding 7T are found. m, coercivity HC and uniaxial magnetic anisotropy KU for these films. Values of m for Mn3Ge films grown on TIT underlayers are close to those theoretically predicted for bulk Mn3Ge  between Cr and Mn3Ge.3Ge ref. , but m i3Ge Heusler compound, and the free electrode from an ultrathin layer of CoFeB with a composition of 20:60:20. Before patterning, these films were post-annealed at 350 °C for 60 min in a high-vacuum chamber using an applied magnetic field of 1T directed out of the plane of the sample. Devices with sizes of 1 × 2 μm2 and ∼30 nm in diameter were fabricated by optical lithography and e-beam lithography, respectively. Only the free layer was patterned to define the junction size while the reference layer was not patterned.MTJ devices were fabricated using standard lithographic techniques from film stacks whose structures are illustrated in H measured at 300 K  and 3 K (larger squares) for patterned MTJ devices (1 × 2 μm2) using TI and TIT underlayers. In each case high applied magnetic fields (±9 T) are needed to align the magnetic moments of the Mn3Ge and CoFeB layers parallel to each other (P state) because of the giant uniaxial anisotropy of Mn3Ge. The junction resistance is higher in the P state compared with the antiparallel (AP) state, obtained when the CoFeB moment switches close to zero field. Thus, the TMR ([(RAP-RP)/RAP] × 100) is negative with values of∼−35% at 300 K and∼−74% at 3 K, where RP and RAP are the junction resistances in the P and AP states, respectively. These are the highest values of TMR reported to date in perpendicularly magnetized MTJ devices using a tetragonally distorted Heusler compound as a magnetic electrode. Nonetheless, these values are much smaller than those predicted by density functional theory (DFT) calculationsRAP barely changes, while RP increases monotonically as T decreases, resulting in higher TMR at low temperatures  for both the regular and inverse structures and for ferri- and ferromagnetic configurations. Surprisingly, ∼40% of these compounds are calculated to be tetragonal in their ground state. Rank ordering these tetragonal compounds according to the combination of the energy difference between the tetragonal and cubic structures and that between the inverse and regular structures, we identified ∼30 possible candidate tetragonal materials, where the average energy difference exceeded ∼0.3 eV per formula unit. Of these, we prepared eight in thin film form using the same buffer layers and deposition conditions as discussed above. Half of these compounds showed a tetragonal structure and two showed excellent PMA properties, namely, Mn2CuSb and Rh2CoSb films grown using either TI underlayers  but TMR curves measured on 1 × 2 μm2 size devices show only very small TMR values of∼−1% . Note that we use bcc Fe rather than CoFeB that is used in the experiments to simplify the calculations. The TMR for Mn3Ge/MgO/Fe MTJs is shown in NMgO, for NMgO≥2. Two definitions of TMR are shown: (TP−TAP)/min, that can vary from −∞ to ∞,  and (TP−TAP)/(TP+TAP), that can vary from −1 to 1. Here TP and TAP are the transmission functions  corresponding to the P and AP states, respectively. The most important result is that the TMR depends sensitively on the atomic configuration of the termination layer in the Mn3Ge adjacent to the MgO tunnel barrier. The calculation gives magnetic moments of +4.08 and −3.12 μB for the Mn–Mn and Mn–Ge termination layers, respectively. The TMR has opposite signs for the two termination layers, Mn–Mn and Mn–Ge, increasing in magnitude with NMgO for Mn–Mn but decreasing in magnitude for Mn–Ge. These results can be understood from the layer dependent, spin-dependent density of states calculated for the bulk electronic structure of Mn3Ge, and the well understood symmetry spin-filtering properties of the MgO/Fe interface. The spin polarization of the native termination layers is negative in both cases but much bigger for Mn–Ge . The negative TMR is consistent with our experimental measurements. Note that due to the large 10.5% lattice mismatch between MgO and Mn3Ge the Brillouin zone filtering effect, which critically depends on the existence of the well-defined 2D Brillouin zone of the Mn3Ge/MgO interface, is likely more suppressed in actual devices as compared with the large negative spin polarization effect that is less sensitive to the existence of the 2D Brillouin zone. Thus, both ideal crystal theoretical simulations  is larger than that for the Mn–Cu layer (−2.8 μB). Interestingly, the tunnelling spin polarization from the native termination layers, that is, in the limit of NMgO→0, is of the opposite sign to the magnetic moment direction of these layers, whereas for Mn3Ge the spin polarization is negative for both terminations (NMgO≤12), tunnelling spin polarization is parallel and antiparallel, to the magnetic moment of the respective termination layer for Mn3Ge and Mn2CuSb, respectively. Moreover, there is no significant Brillouin zone filtering effect for Mn2CuSb/MgO. In this case the dependence of the TMR on NMgO is due to the symmetry spin filtering effect from MgO/Fe, as can be seen from 2CuSb/MgO/Fe, for both terminations, with that for Fe/MgO/Fe. For the Mn2CuSb/MgO/Fe MTJ a negative TMR is predicted for the termination layer with the largest magnetic moment (Mn–Sb) whereas for Mn3Ge/MgO/Fe the opposite is the case. The TMR calculated for an MTJ with equal areas of Mn–Cu and Mn–Sb terminations is shown in NMgO>2). The negative sign of TMR and its small value agrees with our experimental findings.The calculated TMR versus inations . But for3Ge and Mn2CuSb. However, the tunnelling spin polarization can be aligned either parallel, as in the case of Mn3Ge, or antiparallel, as in the case of Mn2CuSb, to the magnetization of the termination layers. We conclude that the most interesting and technologically useful ferrimagnetic Heusler materials will have termination layers with the same tunnelling spin polarization, that is, for one termination layer the tunnelling spin polarization is parallel to the magnetization, and for the other it is the opposite. Such materials can be identified by the use of computational techniques.In summary, we have shown a method to grow highly textured ferrimagnetic Heusler films with large perpendicular anisotropy on amorphous substrates, thereby opening a path to their potential use for many applications such as magnetic recording media and rare-earth-free hard magnets. However, we find that the TMR is strongly influenced by unavoidable atomic steps at the tunnel barrier interface. When the two termination layers have opposite tunnelling spin polarizations they compensate one another leading to low TMR, as we have shown is the case for both Mn3Ge and Mn2CuSb films were deposited by d.c.-magnetron sputtering or ion-beam deposition at temperatures that were varied from ambient to 550 °C. TaxN films were deposited with different Ar/N2 ratios by reactive magnetron sputtering from a Ta target, and 200 Å IrMn3 films were deposited using ion beam sputtering from a IrMn3 target. TaxN and IrMn3 layers were grown at room temperature. Film compositions were measured by Rutherford back scattering measurements. X-ray diffraction measurements were carried out using a Bruker GADDS or a Bruker D8 Discover system. For the Ar/N2 ratios within the range 95/5–75/25, all IrMn3 films on TaxN had a preferential orientation of (001). IrMn3 film grown on pure Ta underlayer showed a (111) orientation. Atomic force microscopy film characterization was made with a Bruker Icon Dimension with ScanAsyst system. High-resolution transmission electron microscopy and electron energy loss spectroscopy studies were made using a JEOL ARM 200F with a Cold-FEG source operated at 200 keV. Magnetic properties were measured at 300 K using a quantum design superconducting quantum interference device vibrating sample magnetometer (SQUID-VSM) in magnetic fields of up to ±7 T in both in-plane and out-of-plane directions. Uniaxial magnetic anisotropy KU values were calculated from KU=Heff × MS/2+2πMS2 (Heff being the effective magnetic field and MS the saturation magnetization).Mn2O3. Electrical contacts were formed from 50 Å Ru/650 Å Au. TMR of the patterned devices was measured using a Quantum Design DynaCool physical property measurement system and a custom-built probe station with Keithley source metres 2,602 and 2,400. For fast evaluation of TMR, RAP and RP values in MTJ devices were encapsulated in Al3Ge/MgO/Fe, Mn2CuSb/MgO/Fe and Fe/MgO/Fe MTJs were calculated using a tight-binding linear muffin-tin orbital method in the atomic sphere approximation with the local density approximation of DFT for the exchange-correlation energy173Ge/MgO/Fe MTJ, the in-plane lattice constant was fixed to the experimental lattice constant a of bulk tetragonal Mn3Ge . For Mna=3.95 Å .3Ge/MgO and Mn2CuSb/MgO interfaces  were determined using the VASP molecular dynamic program3Ge/MgO interface .Supplementary Figures 1-8, Supplementary Notes 1-8 and Supplementary References.


Numerous acute reperfusion therapies (RPT) are currently investigated as potential new therapeutic targets in acute ischemic stroke (AIS). We conducted a comprehensive benefit–risk analysis of available clinical studies assessing different acute RPT, and investigated the utility of each intervention in comparison to standard intravenous thrombolysis (IVT) and in relation to the onset-to-treatment time (OTT).A comprehensive literature search was conducted to identify all available published, peer-reviewed clinical studies that evaluated the efficacy of different RPT in AIS. Benefit-to-risk ratio (BRR), adjusted for baseline stroke severity, was estimated as the percentage of patients achieving favorable functional outcome  or functional independence  at 3 months divided by the percentage of patients who died during the same period.n = 13) and nonrandomized (n = 5) clinical studies fulfilled our inclusion criteria. IV therapy with tenecteplase (TNK) was found to have the highest BRRs , followed by sonothrombolysis (BRR1 = 2.75 and BRR2 = 3.38), while endovascular thrombectomy with MERCI retriever was found to have the lowest BRRs . A second degree negative polynomial correlation was detected between favorable functional outcome and OTT  indicating the time dependency of clinical efficacy of all reperfusion therapies.A total of 18 randomized (Intravenous thrombolysis (IVT) with TNK and sonothrombolysis have the higher BRR among investigational reperfusion therapies. The combination of sonothrombolysis with IV administration of TNK appears a potentially promising therapeutic option deserving further investigation. Intravenous thrombolysis (IVT) with recombinant tissue plasminogen activator (tPA) remains the only approved therapy for acute ischemic stroke that can reverse neurological deficits and improve functional outcome  is worth the risk to the patient, taking into account the potential benefits of a successful outcome because of this particular procedure .We conducted a comprehensive literature search through the MEDLINE,  and the Internet Stroke Center databases to identify all available clinical studies that assessed different RPT in acute ischemic stroke. Our search strategy was based on the combination of terms: “stroke,” “cerebral ischemia,” “thrombolysis,” “recombinant tissue plasminogen activator,” “alteplase,” “tenecteplase,” “thrombectomy,” “sonolysis,” and “sonothrombolysis.” Last literature search was conducted on February 21st, 2014.Studies were included in the qualitative analysis if they presented published and peer-reviewed results from Phase 2 or later, randomized or multicenter controlled trials. Reference lists of all articles that met the inclusion criteria and references of relevant review articles were examined to identify studies that may have been missed by the initial database search. References of retrieved articles were also screened. Duplicate publications were excluded from further evaluation.We evaluated data and conducted a benefit–risk analysis from the studies that provided the following data for each group  within the study:Admission or baseline stroke severity quantified by the National Institutes of Health Stroke Scale (NIHSSb),Time elapsed from OTTIncidence of symptomatic intracranial hemorrhage (sICH)Incidence of mortality/death90-days posttreatment modified Rankin Scale scores (90d mRS)A favorable functional outcome (FFO) was defined as a mRS score of 0–1 at 3 months following stroke onset. Functional independence (FI) was documented as a mRS score of 0–2 at 3 months. Dependency was categorized as a mRS score of 3–5, and death was defined as a mRS score of 6.The benefit-to-risk ratios (BRRs), adjusted for baseline stroke severity, were then estimated separately for all different arms of each study using the following formulas: The numerator in the first term of the formulas above expresses the measure of benefit in which the patient has FFO (mRS = 0–1) or FI (mRS = 0–2) at 90 days after stroke onset, while the denominator indicates the percentage of deceased patients during the same study period. As baseline stroke severity is a known predictor of 3-month outcome . The Statistical Package for Social Science version 13.0 for Windows  was used for statistical analyses.A total of 18 separate randomized (13 studies) or observational (5 studies) clinical trials fulfilled our prespecified inclusion criteria. These studies were evaluating IVT with tPA  indicating that approximately two thirds (64%) of the variation in FFO at 3 months across different trials of RPT can be explained by differences in OTT. Interestingly, no association (P = 0.527) was detected between mortality and OTT  trial  should be first tested and proven to be superior  against rT-PA before investigating the combination of these modalities against the current standard of care.


In addition, their rapid large scale synthesis at room temperature makes these organic semiconducting nanorods highly attractive for advanced optoelectronic device applications. Here, we report low-cost large-area flexible photoconductor devices fabricated using C60 nanorods. We demonstrate that the photosensitivity of the C60 nanorods can be enhanced ~400-fold via an ultralow photodoping mechanism. The photodoped devices offer broadband UV-vis-NIR spectral tuneability, exhibit a detectivitiy >109 Jones, an external quantum efficiency of ~100%, a linear dynamic range of 80 dB, a rise time 60 µs and the ability to measure ac signals up to ~250 kHz. These figures of merit combined are among the highest reported for one dimensional organic and inorganic large-area planar photoconductors and are competitive with commercially available inorganic photoconductors and photoconductive cells. With the additional processing benefits providing compatibility with large-area flexible platforms, these devices represent significant advances and make C60 nanorods a promising candidate for advanced photodetector technologies.One dimensional single-crystal nanorods of C One dimensional 1D) nanostructures have received significant interest in recent years for their potential application in a variety of flexible optoelectronic devices including field effect transistorsD nanostr89101360 nanorods. The devices display photosensitivity across the UV-vis-NIR spectrum with a detectivity, D*, of >109 Jones. To achieve this remarkable level of performance we introduced an ultralow photodoping mechanism, using both organic and inorganic photodopants, which significantly enhances the photosensitivity of the C60 nanorods. Upon excitation these photodopants fulfill two roles. Firstly they fill trap states in the C60 nanorods via interfacial electron transfer thereby increasing the photoconductivity. Secondly, once all trap states are filled, the transferred electrons significantly contribute to the overall photocurrent generation while the holes remain trapped in the photodopant. These two processes enable devices to achieve an external quantum efficiency EQE(λ) ~100%. We find that photodoping increases the detectivity of C60 nanorod devices by up to 2 orders of magnitude to reach a detectivity >109 Jones, whilst also displaying a wide linear dynamic range (LDR) of 80 dB along with photodetection capability up to modulation frequencies of ~250 kHz. These figures of merit obtained for C60 nanorod devices makes them highly attractive for a low-cost photodetector technology. In addition, we demonstrate that these photodetectors can be fabricated on flexible substrates using a simple planar interdigitated electrode architecture under ambient air conditions at room temperature. Such planar photodetectors can be easily integrated with complementary metal-oxide-semiconductor (CMOS) technology, and unlike photodiodes they only require a single metal electrode deposition step. They also eliminate the need to use transparent substrates or electrodes thus reducing the overall cost of the photodetector.Here, we report large-area flexible photoconductor devices fabricated using 1D C60 nanorods were prepared via the fast liquid-liquid interfacial precipitation (FLLIP) method60 powder (purity 99.9%) was dissolved in m-xylene to form a solution with concentration ~2.2 mg mL−1. The C60 solution (2 ml) was then slowly added to 3 mL of isopropyl alcohol (IPA) with the solution instantly turning a brownish-yellow color indicating the formation of a suspension of 1D C60 nanorods. 60 dissolved in m-xylene and the C60 nanorods obtained via FLLIP method. FLLIP method facilitates rapid large scale preparation of C60 nanorods at room temperature and takes less than 10 seconds. A SEM image of the 1D C60 nanorods obtained using the FLLIP method is shown in 60 nanorods was found to be 18 µm and 350 nm respectively, 60 nanorod film onto 10 µm wide interdigitated gold (Au) electrodes with 10 µm spacing, on flexible polyethylene-2,6-naphthalate (PEN) substrates. A SEM image of a typical as deposited C60 nanorod film is shown in 60 nanorod flexible photoconductor devices is shown in 60 dissolved in m-xylene and of a C60 nanorod film are shown in 60 nanorods display a significantly broadened and extended absorption spectrum in comparison with C60 to provide spectral coverage up to 750 nm. The large (~100 nm) redshift of the absorption in the solid state with respect to solution is attributed to enhanced Coulombic interaction between the C60 molecules60 nanorods as a photosensitive material. The responsivity, R(λ), of a photoconductor is defined as the ratio of the photocurrent generated, phI, to the incident optical power, lightP, 60 nanorod photoconductor devices at an applied electric field of 10 Vµm−1 is shown in 60 nanorod absorption spectrum, with a maximum responsivity of 0.85 mAW−1 obtained ~488 nm. The external quantum efficiency (EQE(λ)) can be obtained from R(λ)using the h is Plank's constant, c is the speed of light, q the elementary charge and λ the wavelength of incident light. To compare photodetectors of varying active area and device geometry the detectivity, D*, figure of merit is often used and is given by A is the active area of the device and NEP is the noise equivalent power defined as the optical power at which the signal-to-noise ratio (SNR) is unity, and thereby giving the limit of detection, and is obtained using nI is the spectral noise current density and R(λ) is the responsivity. The C60 nanorod photoconductor device exhibits a peak D* of ~3.8 × 107 Jones at 488 nm. This is surprisingly high detectivity for 1D organic material considering that the devices were fully fabricated and characterized in air without any optimization. Typically, due to the tendency of C60 to randomly crystallize when used in solution, C60 film deposition is usually carried out by vacuum evaporation restricting its application in many devices and adding to fabrication cost. In contrast, C60 nanorods offer compatibility with solution processing, including roll-to-roll processing, and contact printing. The high photosensitivity extending across the full visible spectrum clearly demonstrates the significant potential of C60 nanorods in other applications as well including photovoltaic cells and electrophotography.C60 is a n-type semiconductor and the introduction of traps in C60 due to intercalation of oxygen is well-known2460 nanorod photoconductor device is irradiated with photons the majority of excited electrons are localized in the trap states rather than contributing to the photocurrent, reducing the responsivity. This can be addressed by the injection of additional charge carriers to fill these trap states either by increasing the applied bias or through illumination of the devices with a high light intensity such that the number of excited electrons exceeds the density of traps  (P3HT), rhodamine 6G (R6G), 7,7,8,8-tetracyanoquinodimethane (TCNQ) and inorganic semiconductor NCs (CdSe and PbS). The optical absorption spectrum of the photodopants is shown 60. Photodoping was achieved via sensitizing C60 nanorods with ultralow volumes of photodopants. The responsivity spectra obtained for P3HT and CdSe NC photodoped photoconductor devices is shown in −1 at ~617 nm. The use of P3HT as the photodopant provides a ~400-fold improvement in the responsivity peaking at ~340 mAW−1. The spectral responsivity of the PbS NCs photodoped devices as a function of applied electric field and wavelength is shown in −1 at ~480 nm, whilst also displaying broadband UV-vis-NIR photosensitivity from 350 nm to 1150 nm.To investigate the effect of photodoping on C60 nanorods. This is achieved via an ultralow photodoping mechanism. A transmission electron microscope (TEM) image of ultralow photodoped C60 rod with CdSe NCs is shown in 60 films has been shown to fill C60 traps and thereby increase the electron mobility by more than 3 orders of magnitude60 nanorods can be enhanced significantly such that devices approach responsivity values close to commercial photodetectors. Moreover, such a type of ultralow photodoping enables devices to achieve a photoconductive gain.It should be noted that the photodoped devices we report here work on a fundamentally different mechanism as compared to more commonly reported planar heterojunction donor/acceptor (D/A) devices reported previously2930313260 nanorods device, 60 nanorod device. Interestingly, the responsivity spectrum of all the three photodoped devices still display the similar peaks at ~520 nm, ~620 nm and ~680 nm, which were observed in the undoped C60 nanorods. These peaks correspond to the characteristic absorption peaks of C60 and are also present in the optical absorption of the C60 nanorod film, Fig 2e60 nanorods remain the primary origin of the photocurrent even in photodoped devices. The role of the additional electrons supplied by the photodopants is to pacify the deep trap states present in the C60 nanorods, thereby increasing the C60 electron mobility263460 films and C60 nanorods electron transport is hampered due to presence of high density of traps. However, via an ultralow doping mechanism and careful selection of dopants and photodopants, both mobility and the photoconductivity of such trap rich molecular organic semiconductors can be enhanced by orders of magnitude. It is observed that in the CdSe NC photodoped device there is an additional enhancement in the responsivity between ~550 nm and 650 nm corresponding to the CdSe NC absorption. This implies that CdSe NCs are donating sufficient electrons to saturate the C60 trap states with a surplus of donated electrons directly contributing to the photocurrent.To validate that the enhancement observed in the responsivity of the doped devices occurs due to a photodoping mechanism, we compare the responsivity spectrum of all the photodoped devices with that of the undoped C60, 60 forms a type-II heterojunction and strongly favors photoinduced electron transfer from P3HT to C60. The transfer of holes from the photodopant (P3HT or the semiconductor NCs) to C60 is energetically forbidden, 60 nanorods via the interfacial electron transfer process. As discussed above these transferred electrons primarily are utilized to fill the high density of traps present in the C60 nanorods. The transferred electrons may recombine back with the ground state parent hole via the interfacial recombination process. As the C60 traps begin to fill, subsequently the Fermi energy level is also raised towards the C60 lowest unoccupied molecular orbital (LUMO). Meanwhile, this process facilitates the photoexcited electrons generated in C60 to fully contribute to photocurrent, which were previously localized in the absence of any photodopant, and this is clearly reflected in the enhanced responsivity spectra of all the doped devices. Once all the traps are filled, that is when the number of donated electrons equals the density of traps, the Fermi level approaches the bottom of the C60 LUMO. At this point any subsequently donated electrons from the photodopants contribute to the overall photocurrent generation, 60 nanorod device are higher than commercially available silicon carbide (SiC) or gallium nitride (GaN) ~200 mAW−1 and close to silicon (Si) ~500 mAW−1 photodetectors used for UV and visible light detection respectively with the added advantage of large-area, flexible substrate compatibility and room temperature processing.We now discuss the working mechanism of the organic and inorganic photodoped devices, using P3HT as an example. When the photoconductor device is photoexcited, excitons are generated in both P3HT and C60 nanorods a photodopant was chosen such that it absorbs light beyond the optical absorption range of C60 nanorods. PbS NCs display a size-tunable optical absorption from near UV to NIR via quantum confinement and are widely used in photovoltaic cells and photodetectors to harness NIR photons3860 nanorods absorb (350–750 nm) the device displays a high responsivity, closely following the C60 nanorod absorption spectrum. In this spectral range the working mechanism of the device is similar to that of P3HT or CdSe NCs doped device . This confirms that charge transport in these photodoped photoconductor devices occurs through C60 nanorods and they are the origin of the electric field dependent photocurrent in these devices. The study on other materials used as photodopants including R6G and TCNQ is provided in the In order to gain deeper insight of the photodoping mechanism in Cd device , and furEQE(λ) of the P3HT and PbS NCs photodoped device is shown in −1, the EQE(λ) remains below ~10% and ~2% for P3HT and PbS NCs photodoped devices, respectively. However, for both devices the EQE(λ) is significantly enhanced across the visible region as the applied electric field is increased, reaching maximum values of ~100% at 415 nm and ~30% at 471 nm for the P3HT and PbS NC photodoped devices at 10 Vµm−1. It is noticeable that in the spectral range (730–1150 nm) the EQE(λ) of the PbS NCs photodoped device remains below ~2% even with the increase in the applied electric field. This suggests that for C60 nanorod photoconductors to operate efficiently, photoexcited electrons from both photodopant and the C60 nanorods must contribute to the overall photocurrent generation. Nevertheless, unlike conventional organic photodiodes, which cannot achieve an EQE(λ) ~100%, unless phenomenon such as singlet exciton fission is exploitedEQE(λ) ~100% and is among the best reported for organic single-crystal large area devicesG is the photoconductive gain, τ is the lifetime of trapped charge carrier, TTτ is the transit time, μ is the mobility, ι is the distance between electrodes and E is the applied electric field. From 60 nanorod trap states by the use of photodopants enhances the electron mobility in C60 nanorods thus enabling the high responsivities obtained and the possibility of achieving gain. Using an average value for the electron mobility in C60 single-crystals2V−1s−1 the transit time, TTτ, can be estimated as ~2 ns for applied electric field strength of 10 Vµm−1. As the holes are trapped in the photodopant the mobile electrons can circulate many times in the circuit providing τ > τTT which may be achieved under the influence of an applied electric field. It should be noted that although the EQE(λ) of the device approaches ~100% at high applied fields, it typically remains below ~60% across the whole spectral range up to an applied electric field of 8 Vµm−1. A sharp rise in EQE(λ) between 350–540 nm is observed when the field is increased to 10 Vµm−1. This increase in EQE(λ) in this region is a distinctive signature behavior of electric field-dependent photoconductivity in C604360 devices (operating as a photoconductor due to hole trapping) reported a dramatic increase in EQE(λ) in this region from ~30% at 4.5 Vµm−1 to ~5000% at 35 Vµm−1 and was attributed to photomultiplication phenomena4460 occurs due to Frenkel exciton (intramolecular) disassociation when exciting above ~530 nm, whilst when exciting in the spectral range 350–540 nm the origin of photoexcited carriers is due to electric field assisted dissociation of charge transfer (CT) states (intermolecular)EQE(λ) to 100% in our devices and it might therefore be associated with this mechanism.The 60 nanorod only and the photodoped C60 nanorod photoconductor devices is shown in −1, modulation frequency of 235 Hz, and for an active area of 25 mm2. The photodoped photoconductor devices show greater than an order of magnitude increase in detectivity over the undoped devices. An increase in peak detectivity from 3.8 × 107 Jones to 2.2 × 108, 4 × 108, and 2.3 × 109 Jones is obtained when doping with CdSe NCs, P3HT and PbS NCs respectively, and are for example suitable for low cost imaging and video applications4760 nanorod device is found to extend over five orders of magnitude (100 dB) within which a LDR of 80 dB (over four orders of magnitude) is found. This 80 dB LDR is above that required for most imaging applications and is even higher than reported inorganic and hybrid photoconductor device3960 excitonic lifetime and the photodopant hole trapping. As a result excellent device responsivity is maintained even under high light intensities and thereby providing a wide LDR. The observed LDR exceeds the requirements for the replacement of charge-coupled device (CCD) imaging sensors, is above that of commercially available GaN (50 dB)The detectivity of the Cable GaN  dB50 and−160 nanorod photoconductors promising candidates for high dynamic range (HDR) large-area flexible image sensing technology.In many applications, such as optical switching, the photoconductor temporal response is of high importance. The normalized photocurrent response of a typical photodoped device under modulated ~514 nm excitation at 13 Hz and 50 kHz is shown in 60 nanorods using a room temperature solution processable and rapid procedure undertaken in air. C60 nanorods intrinsically are highly photosensitive, however the introduction of high density of traps primarily due to intercalation of oxygen drastically affect their photosensitivity. This was addressed by introducing an ultralow organic and inorganic photodoping mechanism which not only enhances the photosensitivity of C60 nanorods by orders of magnitude but also enables devices to achieve photoconductive gain. The figures of merit achieved for C60 nanorods are among the highest reported for 1D organic nanostructures and even exceed commercially available photodetectors. These C60 nanorod photoconductor devices represent a significant advance in organic photoconductor technology and their compatibility with large-area flexible device architectures makes them highly attractive for variety of photodetection applications.To summarize, we have shown that low-cost large-area flexible photoconductors can be fabricated employing C−2. The pattern was developed by immersing the UV exposed substrates in the developer (Rohm and Hass MF319 developer) for 3 minutes. Following this, the substrates were washed using de-ionized water, dried with nitrogen, and placed within a sputterer for metal deposition. An adhesion layer (~6 nm) of Titanium (Ti) was sputtered first before deposition of ~120 nm of gold (Au). After metal deposition the substrates were immersed in acetone for the lift-off process to produce the desired interdigitated pattern. C60 nanorod films were then deposited onto the interdigitated planar electrodes from the C60 nanorods solution. Photodoping was achieved via sensitizing C60 nanorods with ultralow volumes (~250 nL) of photodopants P3HT (~6 mg mL−1 in toluene), R6G (~0.5 mg mL−1) CdSe NCs (~2.2 mg mL−1 in toluene), or PbS NCs (~8 mg mL−1 in toluene).Au interdigitated electrodes, 10 μm wide and with inter-electrode spacing of 10 µm  were patterned on a flexible polyethylene-2,6-naphthalate (PEN) substrate via ultraviolet (UV) lithography. Prior to use the substrates were cleaned using acetone and isopropyl alcohol (IPA) respectively for 10 minutes using ultrasonication. Primer and photoresist (Rohm and Hass MICROPOSIT S1813) were then subsequently spin coated onto the substrates at 3500 rpm for 30 seconds. After depositing the photoresist, the substrates were baked on a hot plate (80°C for 1 min). The photoresist coated on the substrates was then exposed to UV light through a pre-patterned mask at an energy dose of ~120 mJ cmR(λ), photocurrent from the biased devices was extracted by measuring the voltage drop across a load resistor connected in series with the device using lock in amplification. Illumination to the devices was provided using chopped monochromatic light obtained from 100 W tungsten lamp and monochromator. Optical filters were used to prevent second order grating reflections illuminating the devices. The optical power falling on the device was measured independently using calibrated Si and InGaAs detectors. Dynamic range measurements were performed using the same set up, illumination to the photoconductor device was given using an Argon ion laser operating at ~514 nm and with the light intensity falling onto the device controlled by varying the laser power. To measure noise current, nI, the devices were placed in an electrically shielded dark box, biased, and the total noise current was measured using a lock in amplifier. The reference frequency was provided by a signal generator with the lock-in amplifier acting as a narrow bandwidth amplifier directly outputting the total noise current. The noise equivalent power (NEP) of the devices was calculated by dividing the measured noise current by the responsivity under identical measurement conditions that is, for the same modulation frequency and the applied electric field. The detectivity, D*, of the devices were calculated by dividing the square root of the active area of the device by the NEP. The detectivity of the photoconductor devices reported was obtained for an applied electric field of 10 Vµm−1 at a modulation frequency of 235 Hz and for an active area of 25 mm2. Frequency dependent transient measurements were recorded using 514 nm Argon ion laser irradiation modulated using an acousto-optic modulator (AOM). The modulation frequency was controlled using a square-wave function generator. The transient response of the devices to pulsed 510 nm illumination was undertaken using a ~8 ns pulse from a Spectra-Physics VersaScan OPO operating at 21 Hz. Transient response measurements were performed with the device biased and the transient photocurrent signal recorded by measuring the voltage drop across a resistor using a digital oscilloscope. Current-voltage characteristics of the devices were measured using a precision source measure unit. Absorption spectra were obtained using a Varian Cary 5000 UV-Vis-NIR spectrophotometer.To obtain the device responsivity, 60 nanorods preparation, device fabrication and device characterization were performed in air at room temperatures.All methods including CR.S. prepared the devices. V.S. performed (HR)TEM studies and analysis. R.S. and R.J.C. performed the device characterization. R.S., V.S. and R.J.C. prepared the manuscript and figures.Supplementary Information


Collective motions of animals that move towards the same direction is aconspicuous feature in nature. Such groups of animals are called aself-propelled agent (SPA) systems. Many studies have been focused on thesynchronization of isolated SPA systems. In real scenarios, different SPAsystems are coupled with each other forming a network of SPA systems. Forexample, a flock of birds and a school of fish show predator-prey relationshipsand different groups of birds may compete for food. In this work, we propose ageneral framework to study the collective motion of coupled self-propelled agentsystems. Especially, we study how three different connections between SPAsystems: symbiosis, predator-prey, and competition influence the synchronizationof the network of SPA systems. We find that a network of SPA systems coupledwith symbiosis relationship arrive at a complete synchronization as all itssubsystems showing a complete synchronization; a network of SPA systems coupledby predator-prey relationship can not reach a complete synchronization and itssubsystems converges to different synchronized directions; and the competitiverelationship between SPA systems could increase the synchronization of each SPAsystems, while the network of SPA systems coupled by competitive relationshipsshows an optimal synchronization for small coupling strength, indicating thatsmall competition promotes the synchronization of the entire system. Groups of animals sometimes display fascinating collective motions –6 in whiIncreasing evidence shows that one system may interact or couple with other systems,such as: different social networks  are interconnected witheach other because the nodes in different networks share the same actors ; transpoβ ∈  denoting the ratio of anode’s the radius in its coupled system to that in its current subsystem.Furthermore, we construct three networks of SPA systems coupled by three types ofinteraction: symbiosis, predator-prey, and competition. Besides, we find that (1)there exits an optimal coupling strength in the coupled systems with symbiotic andpredator-prey relationship to achieve optimal synchronization for each subsystem andthe entire system; (2) furthermore, increasing the radius and absolute velocity anddecreasing of system size could increase the optimal synchronization of everysubsystem and the entire systems; (3) in the systems coupled by competitiverelationships, increasing the coupling strength could increase the synchronizationof each subsystem but decrease the synchronization of the entire system.In this work, we propose a model to show the collective motion in a network of SPAsystems, generalizing the Vicsek model  (VM). InN coupled subsystems of self-propelled agentswith size nk in subsystemk, where the agents in each subsystem move in aL × L square with a same constant speedtowards different directions. Initially, the agents are randomly distributed on theL × L square plane, and theirdirections are also uniformly randomly distributed in the interval . At each time step, the direction of each agent isdetermined by the average directions of all the agent within a circle centered atthe given agent with a radius R  is thetwo dimensional vector of position of agent w at time t,v0 is the absolute speed of each agent andθw(t) isthe direction of agent w at time t. Then itsdirection is updated following z1, z2,…, zl)‖ =(|z1|2 +|z2|2 + … +|zl|2)1/2,△θw ∈ representing thewhite noise, w(t+1) is the set ofneighbors of agent i at time step t+1, defined asVαk indicates that thesubsystem k shows a better synchronization, and whenVαk = 1 all the agent aremoving towards the same direction. A system of two coupled SPA systems (A and B) isshown in Awin system A moves inside a L × L square andits position is . Theneighborhood of node Aw in system B isdefined as Bw in system A is defined asr =β × R. Especially, (i) whenβ = 0, the two SPA systems are separated from each othercorresponding to the case of two isolated SPA systems; (ii) whenβ = 1, the entire system fully mixed with each otherforming a new subsystem with the density being the sum of these two SPA subsystems.When β > 0, an agent w in system Aupdates its direction according to both the agents inΓAw andΩAB,wtogether, and updates its location according to Our model contains radius R  System Aardnorm  defined duced as, 34: Vαkw in system Achanges its direction according to the average values of directions of all theagents in both ΓAw andΩAB,was A symbiotic relationship between two coupled systems benefit the agents of bothsystems . The ageIn the model where SPA systems coupled by predator-prey relationship , withoutThe competitive relationship between two SPA systems has negative effects on bothsince the food, space or other resources that they competing for are limited. Thus, tVs as Vα is thesynchronization degree for the entire system, which denotes the synchronizationof all the agents of n subsystems.Vαw represents thesynchronization of system w. The order parameter not onlyrepresents the degree of each subsystem, but also contains the synchronizationof the entire system.In real world, usually more than two SPA systems are coupled with each other,which is also addressed in this work. As shown in η = 0), we simulate the synchronization of networksof SPA systems coupled by three different relationships, and it can help usunderstand the behavior of a network of n SPA systems.Moreover, we also investigate the effect of the four important parameters on thesynchronization of a network of SPA systems, namely the coupling strengthβ, the radius R, the absolute speedv0, and the system size n. Inthe simulations, we use the periodic boundary condition [ρ =nk/L2= 1. If there is no special statement, we use the parameters asR = 0.3, v0 = 0.1,nk = n = 200for each subsystem and all the results are averaged over 400 realizations.Considering the situation without noise ,indicating that the predator subsystem and the prey subsystem converges to differentdirections as illustrated in βo as a function the radiusR in βo decreases as theradius R increases for each subsystem and the entire system.In n, radius R, and differentvalues of velocity v. As a function of the coupling strength fordifferent system size n, the synchronization of subsystem AVα1 monotonically increasesas the coupling strength β increases, as shown in Vα as a function of thecoupling strength β, we can see thatVα shows a peak at smallβ, indicating that tiny competition can increase thesynchronization of the entire system. This result is as surprising as the resultpresented in We study the synchronization of the paired SPA systems coupled by competitive underdifferent system size Vsas a function of the absolute velocity β for each subsystemand the entire system [β increases. In particular, the totalsynchronization of the entire system is significantly less than each subsystem whenthe coupling strength β increases. The simulation resultsdemonstrate Vs of each subsystem isbetter than the case of the entire system, since the synchronization of one systembenefits the synchronization of another system, but the synchronized direction ofeach subsystem is different from each other. In order to show the optimalsynchronization Vso as a function ofsystem size n, we perform the the numerical simulations in Vso maintain a constant value asthe system size n increases.Besides, we show the synchronization e system . Our simn and the absolute velocity) and the relationship betweendifferent SPA systems (the coupling strength β and theradius R). Moreover, the networks coupled SPA systems coupled bydifferent relationships show different behaviors: (1) the system coupled withsymbiotic relationships shows a complete synchronization, as each subsystem reachinga complete synchronization, under high absolute velocity or high radius; (2) thesystem coupled by the predator-prey relationships shows an optimal but not completesynchronization, while each subsystem can arrive at a complete synchronization; (3)the system of coupled competitive SPA systems shows an optimal synchronization forsmall coupling strength between SPA systems, while no optimal synchronization foreach subsystems. These interesting results can significantly improve ourunderstanding of the synchronization principles of complex systems.SPA systems usually interact or depend on each other, forming networks of SPAsystems. In this work, we propose a model to mimic the synchronization of thenetwork of SPA systems coupled by different relationships: symbiosis, predator-prey,and competition. The synchronization process in the networks of SPA systems could beinfluenced by both the properties of single SPA systems Click here for additional data file.S2 Filev0 various.The simulation results about two subsystems with symbiosis relationship, when(MAT)Click here for additional data file.S3 FileR various.The simulation results about two subsystems with symbiosis relationship, when(MAT)Click here for additional data file.S4 Filen various.The simulation results about two subsystems with predator-prey relationship,when (MAT)Click here for additional data file.S5 Filev0 various.The simulation results about two subsystems with predator-prey relationship,when (MAT)Click here for additional data file.S6 FileR various.The simulation results about two subsystems with predator-prey relationship,when (MAT)Click here for additional data file.S7 Filen various.The simulation results about two subsystems with competition relationship,when (MAT)Click here for additional data file.S8 Filev0 various.The simulation results about two subsystems with competition relationship,when (MAT)Click here for additional data file.


There is considerable speculation concerning the role of the ubiquitous antiphase boundary (APB) defects in magnetite, however, direct information on their structure and properties has remained challenging to obtain. Here we combine predictive first principles modelling with high-resolution transmission electron microscopy to unambiguously determine the three-dimensional structure of APBs in magnetite. We demonstrate that APB defects on the {110} planes are unusually stable and induce antiferromagnetic coupling between adjacent domains providing an explanation for the magnetoresistance and reduced spin polarization often observed. We also demonstrate how the high stability of the {110} APB defects is connected to the existence of a metastable bulk phase of Fe3O4, which could be stabilized by strain in films or nanostructures.The complex and intriguing properties of the ferrimagnetic half metal magnetite (Fe Although Fe3O4 is widely investigated for a variety of applications, the relation between some defects and its properties remains poorly understood. Here, the authors use high-resolution transmission electron microscopy and simulations to determine the atomic structure of the common antiphase boundary defects. It finds diverse applications in areas such as catalysis, rechargeable batteries, magnetic recording, medicine and biology12456893411133O4 is well known a‹100› crystal translations. In one case, this type of model has been used as the basis for first principles electronic structure calculationsAt room temperature, bulk magnetite is a ferrimagnetic inverse spinel  analysis confirming the validity of our predictive approach. This APB has an extremely low formation energy that can be rationalized as it locally resembles a metastable Fe3O4 phase (space group Pmma), which is only 332 meV per formula unit less stable than the room temperature cubic phase. The metastable Pmma phase has to the best of our knowledge never been observed as a bulk phase, but could in principle be stabilized by strain in nanostructures or formed in a non-equilibrium growth processIn this article, we employ first principles-based theoretical modelling to predict the detailed atomic structure, magnetic and electronic properties of stable APB defects in magnetite. Our approach is applied to consider APBs forming on the {110} planes—a common type of APB seen in Fe3O4 follows that which we have employed previously to model extended defects in a range of metal-oxide materials31323O4 . On thermodynamic grounds, one usually expects that APBs with the lowest formation energy will be more common; however, in non-equilibrium growth processes, kinetic factors may also be important making it less straightforward to predict which APB defect is most likely to appear. In the following, all energies are given first for the DFT+ U method, with the DFT values given in parentheses.Our theoretical approach to predict the structure and properties of APB defects in Fe3O4 refs , 35. Cal3O4 refs . Followia[110] and its formation energy is very low, only 102 mJ m−2 (307 mJ m−2). The low formation energy is consistent with the fact that introduction of the APB leads to no net change in Fe coordination . Only the ordering of octahedral and tetrahedral Fe sites between the (111) oxygen planes is modified leading to a relatively small structural distortion near the interface (see −2 (967 mJ m−2). Viewed along the a[100] were not found consistent with the very low frequency of observation of these shifts in filmsFollowing the theoretical search for possible {110} APB structures in magnetite, we find only two stable configurations, which are shown in face see . We note3O4. The Fe3O4 films employed were produced by thermally annealing thin films of Fe2O3 with thicknesses ranging from several nanometres to tens of nanometres under a pressure of 10−4 Pa at 973 K for 1 h. Following this procedure, high-quality Fe3O4 films containing a number of {110} APBs were obtained. To resolve the APB structure with sub-Ångström resolution, high-angle annular dark-field (HAADF) images were taken with a 200-kV scanning TEM (STEM). 15 m−2 forming a network structure. These {110} APBs can be indexed as (110), (011) and 2O4(111) substrates by molecular beam epitaxy methods and find similar agreement with the APB structure  to overcome the exchange interactions across the APB. Analysis of the atomic structure near the interface indicates the presence of Fe(oct)–O–Fe(oct) bonds with an angle of 168°, which are responsible for the AF coupling though the superexchange mechanism  copper is of the order 40–70 mJ m−2 . This provides much needed input into first principles-based micromagnetic simulations of magnetization dynamics in magnetite with relevance for applications in magnetic hyperthermia and spintronic device modelling. We also show how the unusually low formation energy of the APB can be understood in terms of its similarity to a metastable magnetite bulk phase. Although this phase is not predicted to be stable under atmospheric or high pressure, it could be formed in films or nanoparticles as a result of strain or finite-size effects. It is possible that ultrastable APBs may be present in a broader class of similar spinel materials, which are of fundamental and technological significance. Aside from this practical relevance, there has been a great deal of interest in low-temperature charge ordering (Verwey transition) both in the bulk893O4. Studying the influence of 2D APB defects on charge ordering may reveal yet more exotic effects helping to deepen our understanding of these correlated electron systems. The combination of predictive first principles theoretical calculations and high-resolution TEM presented here provides invaluable insight into the atomic structure of the ubiquitous APB defects in Fe3O4 that affect the performance of materials for wide-ranging applications in spintronics, catalysis and medicine.In summary, we have predicted the atomic structure of {110} APB defects in magnetite and find that they are characterized by an extremely low formation energy. The predicted atomic structure of the most stable APB defect has subsequently been verified in all three dimensions by high-resolution electron microscopy highlighting the predictive power of our theoretical approach. Determination of the APB defect structure with such unprecedented atomistic detail has opened the door to prediction of its corresponding electronic and magnetic properties. We note that the properties predicted at the DFT and DFT+ 3O4 as previously used to model extended defects in other oxides such as MgO, TiO2 and HfO2  coordinated Fe ions with formal charge qtet=+3 and the octahedrally coordinated Fe ions as a 50/50 mixture of sites with formal charge qoct=+2 and qoct=+3 . We also simplify the description by considering non-polarizable O and Fe ions. We take the pair potential parameters for O–O and Fe(tet)–O from a previous study that fitted them to give good agreement with the experimental phonon spectrum and crystal structureA parameter in the Fe(oct)–O interaction is refitted to yield the experimental lattice constant of 8.397 Å and the full set of parameters obtained is shown in A parameter for the F(oct)–O interaction is between those previously fitted for +2 and +3 Fe in octahedral sites as expectedwhere =+3 ref. . This moUsing the classical pair potential approach described above, we model (110) APB defects within a periodic supercell as shown in ab initio simulation package42U approach to correct for the self-interaction error. We employ the rotationally invariant DFT+ U formulation of DudarevU−J) for the Fe 3d states is taken as 3.8 eV as was employed in previous studies37−1. For the bulk primitive cell of Fe3O4, a 7 × 7 × 7 Monkhorst–Pack k-point grid and similar k-point densities are employed in the supercell calculations. No symmetry constraints are employed in any of the structural optimizations reported and in general structures are optimized with respect to the positions of all ions and the length and orientation of all cell vectors. The only exception is for the APB calculations where the length of cell vectors parallel to the APB defect plane are fixed at the appropriate bulk values for the given method  and all angles are constrained to 90°. This is to ensure that the structures and formation energies obtained are appropriate for a semi-infinite bicrystal.Spin-polarized (collinear) DFT calculations are performed using the projector augmented wave (PAW) method as implemented within the Vienna 3O4 to be a half-metallic ferrimagnet, while DFT+ U predicts an insulating ferrimagnetic state due to polaronic charge ordering over octahedral iron sites. As discussed by Pinto and ElliottU corresponding to different charge-ordering patterns consistent with the low transition temperature for the Verwey transition. With this method, we predict the lattice constant of the room temperature cubic phase of Fe3O4 to be 8.40 Å using DFT and 8.47 Å using DFT+ U in good agreement with the experiment.We note that DFT predicts the electronic ground state of FeThe formation energy of the APB defects is defined asEAPB is the energy of the supercell containing the two equivalent APB defects, N is the number of Fe3O4 formula units in the supercell, Ec is the calculated cohesive energy of Fe3O4 and A is the area of each APB defect in the supercell. The bulk cohesive energy is calculated using a cell of the same number of atoms and approximate dimensions as the defective supercell to minimize errors associated with differing k-point sampling and basis set quality.where 2O3 with −4 Pa at 973 K for 1 h. Following thermal annealing, the thin-foil TEM samples transformed into the Fe3O4 phase as revealed by the diffraction pattern and TEM and high-resolution TEM (HRTEM) observations, which also shows that the Fe3O4 phase has a good crystallinity.Thin-foil samples of Fe3O4 onto single-crystal MgAl2O4(111) substrates by molecular beam epitaxy methods−10 mbar was achieved. Fe and atomic O were simultaneously deposited using a Knudsen cell and a radio frequency-assisted plasma source, respectively. Film growth has been performed at a nominal rate of 1.2 Å min−1, which has been corroborated by the close agreement of expected and actual  film thicknesses (±10%). During growth, the substrate was held at 350 °C in a partial pressure of 5 × 10−6 mbar of atomic oxygen supplied by the plasma source.We also examined a second type of sample obtained by deposition of Fein situ X-ray photoelectron spectroscopy to differentiate between competing iron-oxide phases and ensure film stoichiometry. Analysis of the Fe3O4/MgAl2O4(111) structure using selected area diffraction established the expected epitaxial relationship, Fe3O4(111)||MgAl2O4(111) and Film growth was monitored in real time using reflective high-energy electron diffraction (RHEED), with RHEED oscillations indicating layer by layer film growth. Chemical analysis was performed using For the thin-foil samples, HAADF-STEM images were taken with a 200-kV STEM  equipped with a probe corrector , which offers an unprecedented opportunity to probe structures with sub-Ångström resolution. A probe current of 30 pA was used for the STEM imaging. The collection angle for the HAADF images was 90–175 mrad.3O4/MgAl2O4(111) sample, HRTEM, selected area diffraction and HAADF-STEM have been performed using a double-aberration-corrected field emission JEOL FS-2200 JEM TEM/STEM and a JEOL-2011 TEM (both operating at 200 kV). Cross-sectional microscope samples were produced by conventional methods, which include mechanical thinning and low-angle Ar ion milling to achieve electron transparency.For the FeHAADF-STEM image simulations have been performed using the multi-slice method implemented in QSTEM image simulation softwareCC=1.6 mm, spherical aberration Cs=0.0011, mm, fifth-order spherical aberration C5=1.756 mm, convergence semi-angle α=24 mrad and HAADF-STEM detector acceptance semi-angle 85–170 mrad. During microscope operation, the twofold astigmatism and focus are continuously corrected by the microscope user and can be identified manually from the live imaging and fast Fourier transforms of the live image. For these simulations, twofold astigmatism has been neglected.The electron beam parameters employed were: acceleration voltage =200 kV, chromatic aberration The atomic coordinates used in this image simulation were taken from the relaxed coordinates of the DFT structural refinement calculations. By expressing the atomic coordinates in slab geometry and considering a number of sequential defect cells along the beam propagation direction, we produce a structural model of sufficient thickness (35.6 nm) such that these simulations represent the likely configuration of a real TEM specimen and reach a point where site intensity in the resultant simulation does not vary significantly from one slice to another. These simulations are performed over 240 projected potential slices of 1.4844 Å thickness, which ensures that the individual atomic planes of this crystal are all kept exclusively within a single computational slice.2 field of interest that includes a full repetition of the bulk Fe3O4 regions away from the structural {110} defect and the defect itself. This region is significantly over-sampled at 0.1 Å per pixel. The effect of thermal diffuse scattering has been modelled using a frozen phonon approximation assuming a room temperature (300 K) specimen. By implementing 30 thermal diffuse scattering iterations in these simulations, we have effectively modelled thermal scattering behaviour. These image simulations are completed by convolution with a Gaussian distribution to simulate the finite electron source size of the microscope and lens instabilities, and rescaling to a 1024 × 1024 pixel arrayThe resultant image simulation is calculated over a 20 Å3O4 films and performed transmission electron microscopy image simulations. C.C. and Z.W. directed by Y.I. synthesized the thin-foil Fe3O4 samples and performed the transmission electron microscopy analysis. The manuscript was written by K.P.M. with input from all co-authors.K.P.M. led the theoretical part of the study and F.H. performed some of the calculations. D.G. and V.K.L. performed electron microscopy analysis of the the molecular beam epitaxy-grown FeHow to cite this article: McKenna, K. P. et al. Atomic-scale structure and properties of highly stable antiphase boundary defects in Fe3O4. Nat. Commun. 5:5740 doi: 10.1038/ncomms6740 (2014).Supplementary Figures 1-4 and Supplementary Discussion.Crystallographic Information File containing the supercell and coordinates for the (110) antiphase boundary defect (model APB-I) optimized using the PBE functional.Crystallographic Information File containing the supercell and coordinates for the (110) antiphase boundary defect (model APB-I) optimized using the PBE+U functional.Crystallographic Information File containing the supercell and coordinates for the (110) antiphase boundary defect (model APB-II) optimized using the PBE functional.Crystallographic Information File containing the supercell and coordinates for the (110) antiphase boundary defect (model APB-II) optimized using the PBE+U functional.Crystallographic Information File containing the supercell and coordinates for the Pmma phase of Fe3O4 optimized using the PBE functional.Crystallographic Information File containing the supercell and coordinates for the Pmma phase of Fe3O4 optimized using the PBE+U functional.


Van Allen radiation belts consist of relativistic electrons trapped by Earth's magnetic field. Trapped electrons often drift azimuthally around Earth and display a butterfly pitch angle distribution of a minimum at 90° further out than geostationary orbit. This is usually attributed to drift shell splitting resulting from day–night asymmetry in Earth's magnetic field. However, direct observation of a butterfly distribution well inside of geostationary orbit and the origin of this phenomenon have not been provided so far. Here we report high-resolution observation that a unusual butterfly pitch angle distribution of relativistic electrons occurred within 5 Earth radii during the 28 June 2013 geomagnetic storm. Simulation results show that combined acceleration by chorus and magnetosonic waves can successfully explain the electron flux evolution both in the energy and butterfly pitch angle distribution. The current provides a great support for the mechanism of wave-driven butterfly distribution of relativistic electrons. Relativistic electrons trapped in the Van Allen radiation belts sometimes exhibit a minimum of their pitch angle distribution at 90°. Here, the authors explain the origin of this phenomenon in terms of chorus and magnetosonic waves through simulations and observations of a geomagnetic storm data. Ek≥1 MeV). Fluxes and pitch angle distributions of relativistic electrons often exhibit dramatic and highly dynamic changes during geomagnetic storms or substorms, which are associated with different physical mechanisms. Those mechanisms include transport, energization and loss processes. Wave–particle interaction plays an important role in energy exchange between various modes of plasma waves and Van Allen radiation belt relativistic electrons. Two types of plasma waves, chorus and magnetosonic (MS) wave , can efficiently accelerate electrons up to relativistic energies. Relativistic electrons can pose serious damage to satellites and astronauts in space, it is therefore important to understand and ultimately predict Van Allen radiation belt electron dynamic variations.The Earth's outer Van Allen radiation belt is composed of trapped electrons with relativistic energy , where the asymmetry becomes substantial. Previous theoretical134Radiation belt trapped electrons experience azimuthal drift-motion around Earth when they bounce between northern and southern magnetic mirror points. Due to the day–night azimuthal asymmetry in Earth's magnetic field, their drift shells which are traced out by their guiding centres can separate radially for different pitch angles, which is known as drift shell splittingL=6–12  occurs during the period 1100 hours on June 28 to 1200 UT on June 29  electrons  from theond L=10 .θ (θ≈0°) and circular polarization (ellipticity≈0)θ≈90°) and linearly polarized (ellipticity≈0)k vector is approximately perpendicular or parallel to the ambient magnetic field directionIn θ  and waveθ . The obsL=4.8 over the interval 1228-1312 UT  electrons from the REPT instrument occurred around -1312 UT , correspin situ measurements of chorus or MS waves were confined to a limited range of magnetic local time (MLT) and L-shells: L=4–6 and MLT=22–24 for chorus; L=2–3.5 and MLT=10–18 for MS.To model the temporal evolution of the electron distribution function, we need to solve the Fokker–Planck diffusion equation, which is associated with pitch-angle and momentum diffusion coefficients driven by wave–particle interaction. Then evaluation of diffusion coefficients needs specific information of wave amplitudes and spectral properties. In this event, due to the brief UT intervals of Van Allen Probes, the L-shells232729L=5.6 for different parameters and MLT regions at the geomagnetic equator , we find that those MS waves display a similar Gaussian distribution to those at L=3 and MLT=17.3 on 29 July. It is therefore possibly reasonable to expect that the MS waves potentially existing at L=4.8 and MLT=19 on 29 July to follow the similar Gaussian distribution to that at L=3 and MLT=17.3.We have also checked the Van Allen Probes data on 28 July 2013 and found that MS waves were indeed observed at θ=86°–89°), distributed in a standard Gaussian form (X=tanθ) with a peak value Xm=tan89°. We noted that a concise modelling method by using maxima wave intensities was adopted in the previous workMeanwhile, for calculating the diffusion coefficients of MS waves, we assume that MS waves propagate very highly oblique  L<5) of the outer radiation belt. This is in contrast to the formation of butterfly distributions at higher locations (L>6) induced by drift shell splitting due to local magnetic field asymmetry. The associated physical processes are schematically presented in L<5 drift azimuthally around Earth inside the magnetosphere without loss to the magnetopause, continuously resonating with chorus and MS waves. The combined acceleration by chorus and MS waves occurs preferably between the medium pitch angles 30° and 60°, leading to the unusual butterfly distribution. The combined acceleration process described here is a universal physical process, which should also be effective in the magnetospheres of Jupiter, Saturn and other magnetized plasma environments in the cosmos.The present modelling provides a further confirmation of wave-driven butterfly pitch angle distribution of relativistic electrons observed by the REPT instrument at lower locations .The basic conditions for the quasi-linear theory are that each individual particle randomly moves in velocity space, resonates with a succession of uncorrelated and small amplitude waves, and is scattered in a small amount in pitch angle and energy each time. Those conditions are basically satisfied in Earth's radiation belts for naturally generated MS and chorus waves, where the MS wave bandwidth is generally above the proton gyrofrequency up to the lower hybrid frequency and the chorus wave roughly lies in the frequency range 0.1–0.8 L=4.8 and MLT=24, relativistic electrons drift eastward around Earth and approach a farthest location L≈5.1 on the dayside. Then they pass the observed location without loss to the magnetopause because the magnetopause locates above L=7.6 in the simulation period. Simulations for different energies or pitch angles (not shown for brevity) indeed show similar results. This indicates that drift shell splitting is unlikely to play a role in the observed butterfly electron distribution in this event.In general, there could be a distorted/stretched geomagnetic field on the nightside during a geomagnetic storm. We have examined the geomagnetic field data from Van Allen Probes and found that the observed data are close to the dipole field model during this storm period. The largest distortion of the dipole field is about 20% in the simulation period. Moreover, we perform a test-particle simulation of trajectories of trapped relativistic (2 MeV) electrons by the TS04 magnetic modelA basic assumption is adopted here that the cold plasma density remains constant and unchanging during the 9-h simulation period. Using the upper hybrid resonance frequency observation from Van Allen Probes, we infer the ambient electron density at locations along Van Allen Probes' orbits and find that the electron density is comparable to the adopted plasma density and does not change much in 9 h. Analogous to the previous workL=4.8, and find no distinct presence of plasmaspheric plume except a slightly higher electron density in the region around/after MLT=16 in the simulation period. The plasmaspheric plume resulting from time-varying convection generally forms with a more structured distribution of plasma in the dusk region in the storm main phase. Meanwhile, the plume moves eastward (towards later MLTs) in Earth's rotation eastward, and gradually fades/erodes as the strength of convection decreases. As shown in To check whether the plasmaspheric plume exists, we analyse the potential data from the Time History of Events and Macroscale Interactions During Substorms (THEMIS) spacecraft at k and frequency ω by the following standard Hamiltonian equationsWe perform the ray tracing of MS waves with wave vector R is the position vector of a point on the ray path, t is the group time, D represents the standard wave dispersion relation obeying D=0 at every point along the ray path. The spatial variation in D can be written:where B0 is the ambient magnetic field and Nc is the background plasma density. We adopt a dipole magnetic field model and the MLT-dependent plasmatrough density modelwhere L>1.4 , with a half-width Xω and a peak Xm. Based on the observation, we choose Xm=tan 89°, Xω=tan 86°, X1=Xm−Xω, X2=Xm+Xω; and the maximum latitude for the presence of MS wave λm=10°. Based on the ray-tracing results  are shown in We consider contribution from harmonic resonances up to ft is calculated by solving the bounce-averaged pitch angle and momentum diffusion equationThe evolution of the electron PSD p is the electron momentum, G=p2T(αe)sinαecosαe with αe being the equatorial pitch angle, the normalized bounce time T(αe)≈1.30−0.56sinαe; 〈Dαα〉, 〈Dpp〉, and 〈Dαp〉=〈Dpα〉 denote bounce-averaged diffusion coefficients in pitch angle, momentum and cross pitch angle–momentum. The explicit expressions of those bounce-averaged diffusion coefficients can be found in the previous work.41here The initial condition is modelled by a bi-modal kappa-type distribution function of energetic electrons49a1 and a2, is expressed as:Each component, with variable weighting parameters nh is the number density of energetic electrons, l indicates the loss-cone index, Γ is the gamma function, κ and mec2 (∼0.5 MeV).here ft=0 at the loss-cone αe=αL(sinαL=L−3/2(4−3/L)−1/4) to simulate a rapid precipitation of electrons inside the loss cone .Supplementary Figures 1-3, Supplementary Table 1, Supplementary Notes 1-2 and Supplementary References


Silver nanoparticles (Ag NPs) are known to exhibit broad antimicrobial activity. However, such activity continues to raise concerns in the context of the interaction of such NPs with biomolecules. In a physiological environment NPs interact with individual biological cells either by penetrating through the cell membrane or by adhering to the membrane. We have explored the interaction of Ag NPs with single optically-trapped, live erythrocytes  using Raman Tweezers spectroscopy. Our experiments reveal that Ag NPs induce modifications within an RBC that appear to be irreversible. In particular we are able to identify that the heme conformation in an RBC transforms from the usual R-state (oxy-state) to the T-state (deoxy-state). We rationalize our observations by proposing a model for the nanoparticle cytotoxicity pathway when the NP size is larger than the membrane pore size. We propose that the interaction of Ag NPs with the cell surface induces damage brought about by alteration of intracellular pH caused by the blockage of the cell membrane transport. One of the most relevant facets of Ag NPs is the broad spectrum of their antimicrobial activities + comprising the Ag NPs + ion binding sites + ion binding For cells that are in proximity of silver nanoparticles there is a high probability of the NPs adhering to the cell membrane. It has been shown that the charge on the silver ion is crucial for its antimicrobial activity; the mechanism is based upon electrostatic attraction between the negatively-charged cell membrane of a micro-organism and the positive charge of the Agi) the binding of nanoparticles to the cell surface and, (ii) the internalization of nanoparticles by specific endocytosis pathways The membrane of a red blood cell (RBC) contains proteins and glycoproteins embedded in a fluid lipid bilayer that exhibits viscoelastic behavior. Sialic acid rich glycoproteins of the RBC membrane are responsible for a negatively charged surface which creates a repulsive electric zeta potential between cells 2, O2, N2) and small molecules  while being impermeable to charged polar molecules and ions  −/HCO3− exchange is carried out by the Anion Exchanger 1 (AE1) or Band 3 protein complex, the Na+/K+ exchange is carried out by sodium-potassium adenosine triphosphatase (NKA-Na+/K+-ATPase), an antiporter enzyme and Na+/H+ exchange is carried out by highly regulated (glyco) phosphoproteins known generically as Na+/H+ exchangers (NHEs) + in exchange for external Na+ is the most effective means of eliminating excess acid from actively metabolizing cells +/H+ exchangers (NHEs) The nature of the lipid bilayer associated with the RBC membrane is amphiphilic, like that of other eukaryotic cells: it is partially or totally permeable to gases (CO+) they release In this study we have investigated the possible effects of the adsorption/ adhesion of Ag nanoparticles (of average diameter 100 nm) on RBC membranes by monitoring Raman spectra with the emphasis on conformational changes in hemoglobin that occur on Ag NP treatment. These type of studies are important from the perspective of revealing both beneficial and adverse effects of nanoparticles in their interactions with living cells, especially in the context of a rapidly expanding nano-bio-technology market. A recent review has cogently listed several aspects of nanotechnological industrialization, exposure, and toxicity of Ag NPs 3 nanoparticles. The AgNO3 nanoparticles used in this study were commercially procured  with specified average particle size of ∼100 nm. The control RBC suspension and NP-treated suspension (maintained in different culture wells) were incubated at 37°C with 5% CO2 for 45 hours. Both the incubated samples were further diluted with phosphate buffered solution (PBS) for Raman Tweezers spectroscopy study. The Raman spectroscopy was performed 20 hours and 45 hours after incubation.Intravenous blood was drawn from healthy, informed volunteers through venipuncture in an EDTA coated vacutainer after obtaining written, informed consent. Ethical approval for the project on “Development of Raman Tweezers for studies on human red blood cells” and, explicitly to draw blood from informed volunteers for this project, was obtained from the University Ethics Committee, Manipal University, on 11 December 2008 (Ref. UEC/35/2008) and renewed on 14th January 2012 . The non-coagulated whole blood was centrifuged at 3000 rpm for 5 minutes to discard the plasma. 100 µl of this blood was diluted in 4 ml of complete RPMI 1640 (RPMI+10% BSA) medium. The RBC suspension was treated with 1 µl, 5 µl and 10 µl of AgNOMicro-Raman spectroscopy of incubated control and Ag NP-treated RBCs was performed using a home-built, single-beam Raman Tweezers set-up. Our set-up uses a tightly-focused 785 nm wavelength laser beam (from a Starbright Diode Laser) to simultaneously trap and excite live RBCs suspended in a biological medium. The tight focusing of our laser beam is achieved using a high numerical aperture (1.3 NA), 100X oil immersion microscope objective of a Nikon Eclipse Ti-U microscope with supportive optics. The scattered Raman signals are directed towards a Horiba JobinYvon Spectrometer equipped with a 1200 gr/mm holographic grating. A Symphony CCD detector is utilized to collect the Raman spectra of trapped cells. The complete system design, specifications, and performance have been discussed elsewhere −1 range. Typical resolution was 5.7 cm−1 and the accuracy with which spectral lines were identified was ±3 cm−1 (0.2 nm).The Raman shifts recorded in the present series of experiments were in the 450–1800 cmet al.et al. In 2 stretching [ν(Fe-O2)] at 565 cm−1, pyrrole half-ring stretching [νsym] at 1370 cm−1, pyrrole deformation mode [δ(pyr deform)sym] at 675 cm−1, venyl deformation mode [δ( = CbH2)4] at 1028 cm−1, the asymmetric stretching mode [ν(CαCm)asym] at 1635 cm−1, the skeletal stretching modes [ν(CβCβ)] at 1520 cm−1, 1545 cm−1 and 1603 cm−1 and finally, the methine C-H deformations [δ(CmH)] at 1211 cm−1 and 1224 cm−1.The major changes that we observe between the average spectra of control and Ag NP (5 µl and 10 µl) treated RBCs are in the vibrations related to Fe-O−1 increases whereas that at 1224 cm−1 decreases in the spectra of 5 µl and 10 µl Ag NP treated RBCs compared to those in control RBC spectra. Both the peaks concurrently originate from the methine ( = CmH−) C-H deformation (ν13) in hemes and are sensitive to the deformation angle of the methine group. −1 to 1211 cm−1. In the Raman spectra of an RBC, this is reflected by a decrease in intensity of the 1224 cm−1 peak and concurrent increase in that of the 1211 cm−1 peak. Wood et al. + concentration. In the T state of hemoglobin the C-terminal histidine (His HC3) of the β-subunits participate in the formation of ion pairs with Asp FG1 +) stabilizes the T-state of hemoglobin. Ion pairs that stabilize the T state of deoxy-hemoglobin must break to form the R state, which is not expected to happen at lower intracellular pH. There are many reports on nanomaterials-cell interaction studies where nanoparticles act as membrane channel blockers et al.We observe that the intensity of the Raman peak at 1211 cm−1) of heme. The increase in intensity of other T-state marker peaks located at 1520 cm−1, 1545 cm−1, and 1603 cm−1, corresponding to the CβCβ skeletal stretching modes in the spectra of 5 µl and 10 µl Ag NP treated RBCs, indicates the presence of more deoxy hemes in these samples −1, corresponding to ν(CαCm)asym in the spectra of 5 µl and 10 µl Ag NP treated RBCs, is an indication of the formation of deoxy hemoglobin, as suggested earlier Significant changes have been observed in the well-known spin-state marker region  in 5 µl and 10 µl Ag NP-treated RBCs spectra. This confirms our view that Ag NP induced distortions in the RBC membrane have permanently transformed most of the hemoglobin molecules in it into the deoxy state 2 peak is also prominent in the average spectra of Control and Ag-treated RBCs recorded after 20 hours of incubation  to statistically differentiate the micro-Raman spectra of control and Ag NP treated cells 20 hours and 45 hours post-incubation. PCA was performed separately on a total of 24 spectra recorded 20 hours post-incubation and on 43 spectra recorded 45 hours post-incubation. −1, 1223 cm−1 and 1635 cm−1) in control RBCs and the deoxygenated state  of hemoglobin in Ag NP (5 µl and 10 µl) treated RBCs. On the other hand, the left panel of 1g mode at 753 cm−1 into two peaks: at 749 cm−1 for pyrrole deformation (ν16) and at 756 cm−1 for pyrrole breathing (ν15).The PC 1 (F1) loadings plots presented in −1, 1249 cm−1, 1389 cm−1 and 1577 cm−1 while peaks at 973 cm−1 and 1370 cm−1, which were already present in the low power spectra, show dramatic increase in intensity. The peaks at 662 cm−1, 973 cm−1, 1249 cm−1, 1370 cm−1, and 1389 cm−1 are identified as heme aggregation markers 10) at 1636 cm−1 and the amide I band at 1771 cm−1 both show the expected power-dependent decrease in intensity. The amide I band is almost missing in the Raman spectra at 15 mW and 20 mW excitation powers, suggesting photo-induced dissociation of polypeptide bonds in proteins. The better resolution spectra recorded in the present experiments establish that, even at high power, the intensity of the 1211 cm−1 peak is less than that of the 1224 cm−1 peak, and that the appearance of the 1249 cm−1 peak does not mask the 1224 cm−1 peak.We also recorded the Raman spectra of RBC at different trapping/excitation powers (at 785 nm) to check the power dependent variations in the spectrum. All the 6 spectra shown in −1 peak appears as a shoulder to the 674 cm−1 peak corresponding to pyrrole deformation. At 20 mW, a peak at 668 cm−1 also accompanies the 662 cm−1 peak. The pyrrole deformation (ν16) peak appears at 747 cm−1 as a shoulder to the 753 cm−1 peak and the 1577 cm−1 peak appears as a shoulder peak to the already present 1583 cm−1 peak of ν37 mode.The 662 cmet al.−1 and 1212 cm−1 along with a concomitant decrease in intensity of peaks at 1224 cm−1 and 1620 cm−1 which are reversible up to the trapping power of 20 mW at 1064 nm. As we know that the photo-induced cell damage is wavelength dependent and decreases as we move towards the infrared region, the damage threshold is more in the case of the 1064 nm laser beam.Ahlawat −1 and 1224 cm−1, are not photo-induced. The power levels that are used to record the Raman spectra of control and Ag NP-treated cells are well below the threshold for occurrence of photo-dissociation and/or heme aggregation. Hence, the spectral changes presented by us in On the basis of our power-dependent measurements it is possible to be certain that the spectral changes observed in the Ag NP-treated RBCs, including the intensity flipping of the peaks at 1211 cmThe information collected by us using Raman tweezers spectroscopy on single, live erythrocytes exposed to the influence of silver nanoparticles (of diameter >100 nm) has revealed that Ag NPs induce irreversible modifications in the heme's conformation through a transformation from the R-state (oxy state) to the T-state (deoxy state). We rationalize our observations by proposing a model for the nanoparticle cytotoxicity pathway when NP's size is larger than the membrane pore size. Specifically, we propose that the Ag NPs interact with the cell surface in such manner that induces damage to the heme molecule in the RBC due to the alteration of intracellular pH caused by the blockage of cell membrane transport.