Development of flexible nanoporous gold electrodes for the detection of glucose

Abstract

The development of implantable glucose sensors is of significant interest in the management of diabetes. This work focuses on developing an implantable, biocompatible nanoporous gold electrode prototype based on Kapton® for the subcutaneous detection of glucose. The electrodes were first modified with a layer containing glucose oxidase and Os(2,2′-bipyridine)₂Cl·PVI (Os(bpy)₂Cl PVI). An additional polymeric layer containing poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) was then added to reduce biofouling and foreign body reaction effects. The modified electrode had a V_MAX of 211 ± 13 μA cm⁻² and a K_Mapp of 6.1 ± 0.8 mM in pseudo physiological conditions, with a linear detection range from 1 to 4 mM and a sensitivity of 28.6 ± 2.1 μA cm⁻² mM⁻¹. In artificial plasma, the response of the sensor was saturated at 3 mM, with a V_MAX of 113 ± 10 μA cm⁻² and a K_Mapp of 2.1 ± 0.4 mM with a linear detection range from 1 to 2.5 mM and a sensitivity of 14.6 ± 3.3 μA cm⁻² mM⁻¹. Mechanical stress testing demonstrated that there was a 40 % reduction of the redox polymer coverage after 320 deformation events, however the catalytic activity was still detectable after 160 events. Minimal cytotoxicity effects of the electrodes were observed. When subcutaneously implanted the electrodes showed fairly good mechanical stability after one week and detachment of the metallic layer on some electrodes after 21 days, probably due to electrode bending. A limited foreign body reaction was observed. These results indicated that the electrodes could be implanted for a period of up to 1 week.