Performance optimisation of porous silicon rugate filter biosensor for the detection of insulin

A porous silicon rugate filter (pSiRF) insulin biosensor has been constructed and systematically optimised by investigating the effects of specific experimental parameters. The pSiRF biosensor is based on an optical sensing platform using interferometric reflectance spectroscopy (IRS) to monitor insulin binding to a surface-anchored insulin binding aptamer (IBA) within the pores. The aim of this study was to determine the optimal fabrication to elicit the maximum sensor response, lowest limit of detection (LOD) and fastest response time. Thermal hydrosilylation with undecylenic acid was used as a base surface modification, with IBA attached through formation of an amide bond. The following pSiRF fabrication conditions were investigated; porous film thickness and IBA concentration in the conjugation solution. The effect of solution flow speed over the pSiRF during insulin biosensing was also investigated in an effort to improve the performance. The optimised pSiRF biosensor was successfully applied for the detection of insulin secreted from human islets on stimulation with glucose. Finally, as a proof of concept, insulin sensing in the presence of human islets on the pSiRF surface was performed to demonstrate the robust performance of the biosensor and the potential for in-situ insulin biosensing.