Watching individual molecules flex within lipid membranes using SERS.

Interrogating individual molecules within bio-membranes is key to deepening our understanding of biological processes essential for life. Using Raman spectroscopy to map molecular vibrations is ideal to non-destructively 'fingerprint' biomolecules for dynamic information on their molecular structure, composition and conformation. Such tag-free tracking of molecules within lipid bio-membranes can directly connect structure and function. In this paper, stable co-assembly with gold nano-components in a 'nanoparticle-on-mirror' geometry strongly enhances the local optical field and reduces the volume probed to a few nm(3), enabling repeated measurements for many tens of minutes on the same molecules. The intense gap plasmons are assembled around model bio-membranes providing molecular identification of the diffusing lipids. Our experiments clearly evidence measurement of individual lipids flexing through telltale rapid correlated vibrational shifts and intensity fluctuations in the Raman spectrum. These track molecules that undergo bending and conformational changes within the probe volume, through their interactions with the environment. This technique allows for in situ high-speed single-molecule investigations of the molecules embedded within lipid bio-membranes. It thus offers a new way to investigate the hidden dynamics of cell membranes important to a myriad of life processes.We acknowledge financial support from EPSRC grant EP/G060649/1, EP/I012060/1, ERC grant LINASS 320503. FB acknowledges support from the Winton Programme for the Physics of Sustainability.This is the final published version. It's also available from Nature Publishing at http://www.nature.com/srep/2014/140812/srep05940/full/srep05940.html

Structural and chemical embrittlement of grain boundaries by impurities: a general theory and first principles calculations for copper

First principles calculations of the Sigma 5 (310)[001] symmetric tilt grain boundary in Cu with Bi, Na, and Ag substitutional impurities provide evidence that in the phenomenon of Bi embrittlement of Cu grain boundaries electronic effects do not play a major role; on the contrary, the embrittlement is mostly a structural or "size" effect. Na is predicted to be nearly as good an embrittler as Bi, whereas Ag does not embrittle the boundary in agreement with experiment. While we reject the prevailing view that "electronic" effects (i.e., charge transfer) are responsible for embrittlement, we do not exclude the role of chemistry. However numerical results show a striking equivalence between the alkali metal Na and the semi metal Bi, small differences being accounted for by their contrasting "size" and "softness" (defined here). In order to separate structural and chemical effects unambiguously if not uniquely, we model the embrittlement process by taking the system of grain boundary and free surfaces through a sequence of precisely defined gedanken processes; each of these representing a putative mechanism. We thereby identify three mechanisms of embrittlement by substitutional impurities, two of which survive in the case of embrittlement or cohesion enhancement by interstitials. Two of the three are purely structural and the third contains both structural and chemical elements that by their very nature cannot be further unravelled. We are able to take the systems we study through each of these stages by explicit computer simulations and assess the contribution of each to the nett reduction in intergranular cohesion. The conclusion we reach is that embrittlement by both Bi and Na is almost exclusively structural in origin; that is, the embrittlement is a size effect.Comment: 13 pages, 5 figures; Accepted in Phys. Rev.

Generalized circuit model for coupled plasmonic systems.

We develop an analytic circuit model for coupled plasmonic dimers separated by small gaps that provides a complete account of the optical resonance wavelength. Using a suitable equivalent circuit, it shows how partially conducting links can be treated and provides quantitative agreement with both experiment and full electromagnetic simulations. The model highlights how in the conducting regime, the kinetic inductance of the linkers set the spectral blue-shifts of the coupled plasmon

Nanooptics of molecular-shunted plasmonic nanojunctions.

Gold nanoparticles are separated above a planar gold film by 1.1 nm thick self-assembled molecular monolayers of different conductivities. Incremental replacement of the nonconductive molecules with a chemically equivalent conductive version differing by only one atom produces a strong 50 nm blue-shift of the coupled plasmon. With modeling this gives a conductance of 0.17G(0) per biphenyl-4,4'-dithiol molecule and a total conductance across the plasmonic junction of 30G(0). Our approach provides a reliable tool quantifying the number of molecules in each plasmonic hotspot, here <200.We acknowledge financial support from EPSRC grant EP/ G060649/1, EP/I012060/1, EP/L027151/1, EP/K028510/1, ERC grant LINASS 320503. F.B. acknowledges support from the Winton Programme for the Physics of Sustainability. C.T. and J.A. acknowledge financial support from Project FIS2013- 41184-P from MINECO, ETORTEK 2014-15 of the Basque Department of Industry and IT756-13 from the Basque consolidated groups.This paper was originally published in Nano Letters under a CC-BY licence (F Benz, C Tserkezis, LO Herrmann, B de Nijs, A Sanders, DO Sigle, L Pukenas, SD Evans, J Aizpurua, JJ Baumberg, Nano Letters 2015, 15, 669−674

Elemental redistributions at structural defects in Cu(In,Ga)Se₂ thin films for solar cells

The microstructural evolution of Cu(In,Ga)Se2 absorber layers during a three-stage-type co-evaporation process was studied to elucidate the effect of a Cu-rich stage on the formation of extended structural defects. Defect densities for two Cu-poor samples, one interrupted before and one after this crucial Cu-rich composition stage, were investigated by scanning transmission electron microscopy (STEM) imaging. The structure and chemical nature of individual defects were investigated by aberration-corrected high-resolution STEM in combination with electron energy-loss spectroscopy on the atomic-scale. In spite of the different defect densities between the two samples, most of the individual defects exhibited similar chemistry. In particular, the elemental distributions of atomic columns at {112} twin planes, which are very frequent in Cu(In,Ga)Se2 thin films, were found to be the same as in the defect-free grain interiors. In contrast, within grain boundaries, dislocation cores, and other structurally more complex defects, elemental redistributions of Cu and In were observed

Common law marriage and couple formation

The Current Population Survey is used to investigate effects of Common Law Marriage (CLM) on whether young US-born adults live in couples in the U.S. CLM effects are identified through cross-state and time variation, as some states abolished CLM over the period examined. Analysis based on Gary Becker's marriage economics helps explain why CLM affects couple formation and does so differently depending on education, sex ratios and parent status. CLM reduces in-couple residence, and more so for childless whites and where there are fewer men per woman. Effects are larger for college-educated men and women without college

Definition and quantification of six immune- and neuroregulatory serum proteins in healthy and demented elderly

AIM: Blood-based biomarkers related to immune- and neuroregulatory processes may be indicative of dementia but lack standardization and proof-of-principle studies. MATERIALS & METHODS: The blood serum collection protocol as well as the analytic procedure to quantify the markers BDNF, IGF-1, VEGF, TGF-β 1, MCP-1 and IL-18 in blood serum were standardized and their concentrations were compared between groups of 81 Alzheimer’s disease patients and 79 healthy controls. RESULTS: Applying standardized methods, results for the quantification of the six markers in blood serum are stable and their concentrations significantly differ for all analytes except VEGF between patients diagnosed with Alzheimer’s disease and healthy controls. CONCLUSION: Analyzing a panel of six markers in blood serum under standardized conditions may serve as a diagnostic tool in primary dementia care in the future. LAY ABSTRACT: Neurodegenerative processes underlie and account for a large portion of dementia cases in the elderly, with Alzheimer’s disease being the most common neurodegenerative disorder. Yet, it is challenging for nonspecialized physicians to assess whether a patients’ cognitive impairment originates in underlying neurodegenerative processes. We show that the combination of six biomarkers quantified in blood can indicate the presence of Alzheimer’s disease, since these markers are not altered in healthy elderly people. Blood biomarkers indicative of neurodegenerative processes may be useful in the future to compile a personalized diagnostic and treatment plan to assess the basis of, and properly treat, cognitive impairment

Controllable Tuning Plasmonic Coupling with Nanoscale Oxidation

This is the final version of the article. It first appeared from the American Chemical Society via http://dx.doi.org/10.1021/acsnano.5b01283The nanoparticle on mirror (NPoM) construct is ideal for the strong coupling of localized plasmons because of its simple fabrication and the nm-scale gaps it offers. Both of these are much harder to control in nanoparticle dimers. Even so, realizing controllable gap sizes in a NPoM remains difficult and continuous tunability is limited. Here, we use reactive metals as the mirror so that the spacing layer of resulting metal oxide can be easily and controllably created with specific thicknesses resulting in continuous tuning of the plasmonic coupling. Using Al as a case study, we contrast different approaches for oxidation including electrochemical oxidation, thermal annealing, oxygen plasma treatments, and photo-oxidation by laser irradiation. The thickness of the oxidation layer is calibrated with depth-mode X-ray photoemission spectroscopy (XPS). These all consistently show increasing thickness of the oxidation layer blue-shifts the plasmonic resonance peak while the transverse mode remains constant, as well matched by simulations. Our approach provides a facile and reproducible method for scalable, local and controllable fabrication of NPoMs with tailored plasmonic coupling, suited for many applications of sensing, photochemistry, photoemission and photovoltaics.EPSRC grant EP/G060649/1, EP/I012060/1, ERC grant LINASS 320503