Electronic structure of the electron-doped cuprate superconductors

Within the framework of the kinetic energy driven d-wave superconductivity, the electronic structure of the electron doped cuprate superconductors is studied. It is shown that although there is an electron-hole asymmetry in the phase diagram, the electronic structure of the electron-doped cuprates in the superconducting-state is similar to that in the hole-doped case. With increasing the electron doping, the spectral weight in the $(\pi,0)$ point increases, while the position of the superconducting quasiparticle peak is shifted towards the Fermi energy. In analogy to the hole-doped case, the superconducting quasiparticles around the $(\pi,0)$ point disperse very weakly with momentum.Comment: 8 pages, 3 figures, accepted for publication in Phys. Lett.

Asymmetry of the electron spectrum in hole-doped and electron-doped cuprates

Within the t-t'-J model, the asymmetry of the electron spectrum and quasiparticle dispersion in hole-doped and electron-doped cuprates is discussed. It is shown that the quasiparticle dispersions of both hole-doped and electron-doped cuprates exhibit the flat band around the (\pi,0) point below the Fermi energy. The lowest energy states are located at the (\pi/2,\pi/2) point for the hole doping, while they appear at the (\pi,0) point in the electron-doped case due to the electron-hole asymmetry. Our results also show that the unusual behavior of the electron spectrum and quasiparticle dispersion is intriguingly related to the strong coupling between the electron quasiparticles and collective magnetic excitations.Comment: 8 pages, 3 figures, typo corrected, added detailed calculations and updated figure 3 and references, accepted for publication in Phys. Lett.

Doping dependence of charge dynamics in electron-doped cuprates

Within the t-t'-J model, the doping dependence of charge dynamics in electron-doped cuprates is studied. The conductivity spectrum shows a pseudogap structure with a low-energy peak appearing at $\omega\sim 0$ and an rather sharp midinfrared peak appearing around $\omega\sim 0.3\mid t\mid$, and the resistivity exhibits a crossover from the high temperature metallic-like to low temperature insulating-like behavior in the relatively low doped regime, and a metallic-like behavior in the relatively high doped regime, in qualitative agreement with experiments. Our results also show that these unusual behaviors of the charge dynamics is intriguingly related to the magnetic correlation in the system.Comment: 5 pages, 3 figures, discussions are added, accepted for publication in Phys. Lett.

Donor/Acceptor Mixed Self-Assembled Monolayers for Realising a Multi-Redox-State Surface

Mixed molecular self-assembled monolayers (SAMs) on gold, based on two types of electroactive molecules, that is, electron-donor (ferrocene) and electron-acceptor (anthraquinone) molecules, are prepared as an approach to realise surfaces exhibiting multiple accessible redox states. The SAMs are investigated in different electrolyte media. The nature of these media has a strong impact on the types of redox processes that take place and on the redox potentials. Under optimised conditions, surfaces with three redox states are achieved. Such states are accessible in a relatively narrow potential window in which the SAMs on gold are stable. This communication elucidates the key challenges in fabricating bicomponent SAMs as electrochemical switches.We acknowledge the financial support of the EU projects ERC StG 2012-306826 e-GAMES, ITN iSwitch (GA no. 642196) CIG (PCIG10- GA-2011-303989), ACMOL (GA no. 618082), the Networking Research Center of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the DGI (Spain) with project BE-WELL CTQ2013- 40480-R and the Generalitat de Catalunya with project 2014- SGR-17. The authors also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496). N.C acknowledges the RyC Program. J.C-M. and E.M. are enrolled in the Materials Science PhD program of UAB.Peer reviewe

Functional role of T-cell receptor nanoclusters in signal initiation and antigen discrimination

Antigen recognition by the T-cell receptor (TCR) is a hallmark of the adaptive immune system. When the TCR engages a peptide bound to the restricting major histocompatibility complex molecule (pMHC), it transmits a signal via the associated CD3 complex. How the extracellular antigen recognition event leads to intracellular phosphorylation remains unclear. Here, we used single-molecule localization microscopy to quantify the organization of TCR–CD3 complexes into nanoscale clusters and to distinguish between triggered and nontriggered TCR–CD3 complexes. We found that only TCR–CD3 complexes in dense clusters were phosphorylated and associated with downstream signaling proteins, demonstrating that the molecular density within clusters dictates signal initiation. Moreover, both pMHC dose and TCR–pMHC affinity determined the density of TCR–CD3 clusters, which scaled with overall phosphorylation levels. Thus, TCR–CD3 clustering translates antigen recognition by the TCR into signal initiation by the CD3 complex, and the formation of dense signaling-competent clusters is a process of antigen discrimination

Electrochemical fluorescence modulation enables simultaneous multicolour imaging

Multicolour fluorescence imaging is crucial to simultaneously visualize multiple targets in cells, enabling the study of complicated cellular processes. Common multicolour methods rely on using fluorophores with sufficiently different spectral or lifetime characteristics. Here we present a new multicolour imaging strategy on a standard fluorescence microscope, where up to four fluorophores with high spectral overlap can be resolved using a single-colour optical configuration. We find that under electrochemical modulation, the fluorophores are regulated between the bright and dim states, with each displaying a distinct fluorescence response pattern. These unique fluorescence potential profiles enable the effective separation of different fluorophores through linear unmixing. We also demonstrate that electrochemical fluorescence switching is readily applicable to four-colour STED imaging. With no modification to the optical setups and easy adaptation to different microscopes, we anticipate that colour unmixing based on electrochemical fluorescence switching will provide an easily accessible multicolour imaging pathway for discoveries in diverse fields

A systematic review of the evidence for single stage and two stage revision of infected knee replacement

BACKGROUND: Periprosthetic infection about the knee is a devastating complication that may affect between 1% and 5% of knee replacement. With over 79 000 knee replacements being implanted each year in the UK, periprosthetic infection (PJI) is set to become an important burden of disease and cost to the healthcare economy. One of the important controversies in treatment of PJI is whether a single stage revision operation is superior to a two-stage procedure. This study sought to systematically evaluate the published evidence to determine which technique had lowest reinfection rates. METHODS: A systematic review of the literature was undertaken using the MEDLINE and EMBASE databases with the aim to identify existing studies that present the outcomes of each surgical technique. Reinfection rate was the primary outcome measure. Studies of specific subsets of patients such as resistant organisms were excluded. RESULTS: 63 studies were identified that met the inclusion criteria. The majority of which (58) were reports of two-stage revision. Reinfection rated varied between 0% and 41% in two-stage studies, and 0% and 11% in single stage studies. No clinical trials were identified and the majority of studies were observational studies. CONCLUSIONS: Evidence for both one-stage and two-stage revision is largely of low quality. The evidence basis for two-stage revision is significantly larger, and further work into direct comparison between the two techniques should be undertaken as a priority

An investigative study of electrochemical induced fluorescence for fluorophores

Understanding and controlling the fluorescence of dye molecules is essential for many applications especially in biological imaging. Electrochemical-induced modulation of fluorescence provides the capability to non-destructively control the fluorescent emission of fluorophores, allowing new avenues to exploit for fluorescence imaging. This paper reports on the investigation of electrochemical-induced fluorescence modulation, focusing on the effect of the fluorophore chemical structure and the buffer composition. Of the twelve fluorophores investigated, it was observed that any variations in the chemical structure results in differences in how the fluorescence is modulated with potential. Our results showed that different core fluorescent structures exhibited distinctive modulation behaviours, the oxazine fluorophore (ATTO 655) was stable in the non-fluorescent configuration causing a prolonged low signal and the coumarin fluorophore (ATTO 390) possessed low response. Certain trends observed are related to the impact of the chemical structure on the fluorescence modulation with potential. For example, the low fluorescence modulation with potential for ATTO 390 suggests that the presence of the electron withdrawing -N+R3 group facilitates significant modulation, while a lack of the -N+R3 group results in low modulation. The unique response of ATTO 655 suggested the element at the radical site can affect the stability of the radical- and leuco-states and influence the fluorescence modulation that occurs. Additionally, the results show that buffer additives, such as oxygen scavengers and triplet quenchers, affect the fluorescence modulation either by stabilising the non-fluorescent radical or leuco-fluorophore structure, or improving photon emission. The quantitative characterisation of electrochemical fluorescence modulation behaviours for various fluorophores provides a guideline for future application of the fluorophores for sensing or imaging based on their performances

Electrochemically controlled blinking of fluorophores for quantitative STORM imaging

Stochastic optical reconstruction microscopy (STORM) allows wide-field imaging with single-molecule resolution by calculating the coordinates of individual fluorophores from the separation of fluorophore emission in both time and space. Such separation is achieved by photoswitching the fluorophores between a long-lived OFF state and an emissive ON state. Although STORM can image single molecules, molecular counting remains challenging due to undercounting errors from photobleached or overlapping dyes and overcounting artefacts from the repetitive random blinking of dyes. Here we show that fluorophores can be electrochemically switched for STORM imaging (EC-STORM), with excellent control over the switching kinetics, duty cycle and recovery yield. Using EC-STORM, we demonstrate molecular counting by using electrochemical potential to control the photophysics of dyes. The random blinking of dyes is suppressed by a negative potential but the switching-ON event can be activated by a short positive-potential pulse, such that the frequency of ON events scales linearly with the number of underlying dyes. We also demonstrate EC-STORM of tubulin in fixed cells with a spatial resolution as low as ~28 nm and counting of single Alexa 647 fluorophores on various DNA nanoruler structures. This control over fluorophore switching will enable EC-STORM to be broadly applicable in super-resolution imaging and molecular counting

The importance of nanoscale confinement to electrocatalytic performance

Electrocatalytic nanoparticles that mimic the three-dimensional geometric architecture of enzymes where the reaction occurs down a substrate channel isolated from bulk solution, referred to herein as nanozymes, were used to explore the impact of nano-confinement on electrocatalytic reactions. Surfactant covered Pt-Ni nanozyme nanoparticles, with Ni etched from the nanoparticles, possess a nanoscale channel in which the active sites for electrocatalysis of oxygen reduction are located. Different particle compositions and etching parameters allowed synthesis of nanoparticles with different average substrate channel diameters that have varying amounts of nano-confinement. The results showed that in the kinetically limited regime at low overpotentials, the smaller the substrate channels the higher the specific activity of the electrocatalyst. This is attributed to higher concentrations of protons, relative to bulk solution, required to balance the potential inside the nano-confined channel. However, at higher overpotentials where limitation by mass transport of oxygen becomes important, the nanozymes with larger substrate channels showed higher electrocatalytic activity. A reaction-diffusion model revealed that the higher electrocatalytic activity at low overpotentials with smaller substrate channels can be explained by the higher concentration of protons. The model suggests that the dominant mode of mass transport to achieve these high concentrations is by migration, exemplifying how nano-confinement can be used to enhance reaction rates. Experimental and theoretical data show that under mass transport limiting potentials, the nano-confinement has no effect and the reaction only occurs at the entrance of the substrate channel at the nanoparticle surface