Vertical-junction photodiodes for smaller pixels in retinal prostheses

Objective. To restore central vision in patients with atrophic age-related macular degeneration, we replace the lost photoreceptors with photovoltaic pixels, which convert light into current and stimulate the secondary retinal neurons. Clinical trials demonstrated prosthetic acuity closely matching the sampling limit of the 100 μm pixels, and hence smaller pixels are required for improving visual acuity. However, with smaller flat bipolar pixels, the electric field penetration depth and the photodiode responsivity significantly decrease, making the device inefficient. Smaller pixels may be enabled by (a) increasing the diode responsivity using vertical p-n junctions and (b) directing the electric field in tissue vertically. Here, we demonstrate such novel photodiodes and test the retinal stimulation in a vertical electric field. Approach. Arrays of silicon photodiodes of 55, 40, 30, and 20 μm in width, with vertical p-n junctions, were fabricated. The electric field in the retina was directed vertically using a common return electrode at the edge of the device. Optical and electronic performance of the diodes was characterized in-vitro, and retinal stimulation threshold measured by recording the visually evoked potentials in rats with retinal degeneration. Main results. The photodiodes exhibited sufficiently low dark current (<10 pA) and responsivity at 880 nm wavelength as high as 0.51 A W-1, with 85% internal quantum efficiency, independent of pixel size. Field mapping in saline demonstrated uniformity of the pixel performance in the array. The full-field stimulation threshold was as low as 0.057 ± 0.029 mW mm-2 with 10 ms pulses, independent of pixel size. Significance. Photodiodes with vertical p-n junctions demonstrated excellent charge collection efficiency independent of pixel size, down to 20 μm. Vertically oriented electric field provides a stimulation threshold that is independent of pixel size. These results are the first steps in validation of scaling down the photovoltaic pixels for subretinal stimulation

Rationale and recommendations on decolonising the pedagogy and curriculum of the Law School at the University of Exeter

This is the final version. Available on open access from Routledge via the DOI in this recordThis report outlines the rationale behind and recommendations on the steps that need to be taken towards decolonising the Law School's pedagogy and curriculum. It concludes a two-year process of research and discussions involving a joint effort between staff and students. A rationale for a change in approach to both pedagogy and curriculum is presented together with recommendations and practical examples of how this might be achieved in modular teaching in the Law School

Direct conjugation of antibodies to the ZnS shell of quantum dots for FRET immunoassays with low picomolar detection limits

International audienceCompact and functional nanoparticle-antibody conjugates are of paramount importance for the development of quantum dot (QD)-based immunoassays. Here, we present a simple strategy to directly conjugate IgG, F(ab')2, and Fab antibodies via their endogenous disulfide groups directly to the inorganic ZnS shell of compact penicillamine-coated QDs. The functionality of the conjugates was demonstrated by terbium (Tb)-to-QD FRET immunoassays against prostate specific antigen in serum samples. Detection limits of 2.5 pM (0.080 ng mL(-1)) were 10 and 25 times lower compared to conjugation via maleimide-terminated ligands and polymer chains, respectively. These more compact, simple, and sensitive QD-antibody conjugates will be highly advantageous for nanocrystal-based biosensing applications

FRET as a biomolecular research tool — understanding its potential while avoiding pitfalls

International audienceThe applications of Förster resonance energy transfer (FRET) grow with each year. However, different FRET techniques are not applied consistently, nor are results uniformly presented, which makes implementing and reproducing FRET experiments challenging. We discuss important considerations for designing and evaluating ensemble FRET experiments. Alongside a primer on FRET basics, we provide guidelines for making experimental design choices such as the donor-acceptor pair, instrumentation and labeling chemistries; selecting control experiments to unambiguously demonstrate FRET and validate that the experiments provide meaningful data about the biomolecular process in question; analyzing raw data and assessing the results; and reporting data and experimental details in a manner that easily allows for reproducibility. Some considerations are also given for FRET assays and FRET imaging, especially with fluorescent proteins. Our goal is to motivate and empower all biologists to consider FRET for the powerful research tool it can be