Novel approaches to engineer glucose biosensors

Abstract

Designing a biosensor capable of continuously monitoring blood glucose concentration in people with diabetes has been a major challenge for over three decades. In this work we attempt to develop a novel microspike based minimally invasive biosensor for this purpose. Also, as a part of an ongoing study, we attempt to improve the current design of coil-type implantable biosensors. Microspikes, which are able to painlessly penetrate the skin layer, were fabricated using lithographic techniques and sputtered with gold to serve as an electrode. The biosensor design is based on thiomalic acid self-assembled monolayer (SAM) on which glucose oxidase was immobilised by a simple coupling technique together with a tetrathiafulvalene mediator entrapped in an epoxy-polyurethane permselective membrane. Functional testing revealed that such modified sensors are capable of detecting glucose concentration within the clinically relevant range. This was followed by studying the microspike based biosensors incorporated into the microfluidics platform mimicking the sensor behaviour in interstitial fluid. Data from these experiments revealed that the sensor response is mainly dependent on enzyme kinetics rather than membrane permeability to glucose. In contrast, an attempt to address the reproducibility issues of coil-type biosensors is presented. The hypothesis for this study was that a crosslinked hydrogel would have a sufficiently uniform porosity and hydrophilicity to address the variability in sensor sensitivity. The hydrogel was prepared by crosslinking di-hydroxyethyl methacrylate, hydroxyethyl methacrylate and N-vinyl pyrrolidone with 2.5 mol% ethylene glycol dimethacrylate using the water soluble initiators – ammonium persulphate and sodium metabisulfite under a nitrogen atmosphere. The hydrogel was applied to the sensor by dip coating during polymerisation. Electrochemical measurements revealed that the response characteristics of sensors coated with this membrane are highly consistent. Scanning Electrochemical Microscopy (SECM) was used to spatially resolve glucose diffusion through the membrane by measuring the consequent hydrogen peroxide release and compared with an epoxy- polyurethane membrane.