• Graphene oxide electrochemistry: the electrochemistry of graphene oxide modified electrodes reveals coverage dependent beneficial electrocatalysis

      Brownson, Dale A. C.; Smith, Graham C.; Banks, Craig E.; University of Chester; Manchester Metropolitan University (The Royal Society, 2017-11-15)
      The modification of electrode surfaces is widely implemented in order to try and improve electron transfer kinetics and surface interactions, most recently using graphene related materials. Currently, the use of ‘as is’ graphene oxide (GO) has been largely overlooked, with the vast majority of researchers choosing to reduce GO to graphene or use it as part of a composite electrode. In this paper, ‘as is’ GO is explored and electrochemically characterized using a range of electrochemical redox probes, namely potassium ferrocyanide(II), N,N,N ,N -tetramethyl-p-phenylenediamine (TMPD), dopamine hydrochloride and epinephrine. Furthermore, the electroanalytical efficacy of GO is explored towards the sensing of dopamine hydrochloride and epinephrine via cyclic voltammetry. The electrochemical response of GO is benchmarked against pristine graphene and edge plane-/basal plane pyrolytic graphite (EPPG and BPPG respectively) alternatives, where the GO shows an enhanced electrochemical/electroanalytical response. When using GO as an electrode material, the electrochemical response of the analytes studied herein deviate from that expected and exhibit altered electrochemical responses. The oxygenated species encompassing GO strongly influence and dominate the observed voltammetry, which is crucially coverage dependent. GO electrocatalysis is observed, which is attributed to the presence of beneficial oxygenated species dictating the response in specific cases, demonstrating potential for advantageous electroanalysis to be realized. Note however, that crucial coverage based regions are observed at GO modified electrodes, owing to the synergy of edge plane sites and oxygenated species. We report the true beneficial electrochemistry of GO, which has enormous potential to be beneficially used in various electrochemical applications ‘as is’ rather than be simply used as a precursor to making graphene and is truly a fascinating member of the graphene family
    • In vitro and Computational Modelling of Drug Delivery across the Outer Blood-Retinal Barrier

      Davies, Alys E; Williams, Rachel L.; Lugano, Gaia; Pop, Serban R.; Kearns, Victoria R.; University of Liverpool; University of Chester
      The ability to produce rapid, cost-effective and human-relevant data has the potential to accelerate development of new drug delivery systems. Intraocular drug delivery is an area undergoing rapid expansion due to the increase in sight-threatening diseases linked to increasing age and lifestyle factors. The outer bloodretinal barrier (OBRB) is important in this area of drug delivery, as it separates the eye from the systemic blood flow. This study reports the development of complementary in vitro and in silico models to study drug transport from silicone oil across the outer blood-retinal barrier. Monolayer cultures of a human retinal pigmented epithelium cell line, ARPE-19, were added to chambers and exposed to a controlled flow to simulate drug clearance across the OBRB. Movement of dextran molecules and release of ibuprofen from silicone oil in this model were measured. Corresponding simulations were developed using COMSOL Multiphysics computational fluid dynamics (CFD) software and validated using independent in vitro data sets. Computational simulations were able to predict dextran movement and ibuprofen release, with all of the features of the experimental release profiles being observed in the simulated data. Simulated values for peak concentrations of permeated dextran and ibuprofen released from silicone oil were within 18% of the in vitro results. This model could be used as a predictive tool of drug transport across this important tissue.