Characterization of novel glucose oxysilane sol–gel electrochemical biosensors with copper hexacyanoferrate mediator

New sol–gel encapsulated glucose oxidase (GOx) enzyme electrodes, constructed from carbon film resistor electrodes and chemically deposited copper hexacyanoferrate as mediator, have been developed and characterized using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The sol–gel was prepared using three different oxysilanes: 3-aminopropyltriethoxysilane (APTOS), 3-glycidoxypropyltrimethoxysilane (GOPMOS) and the well-known tetraethoxysilane (TEOS). The sol–gel composition was optimised for each oxysilane according to the gelation time of the sol–gel solution and response time of the enzyme biosensor to standard additions of glucose. Results obtained showed that APTOS and GOPMOS have similar electrochemical behaviour but differ from TEOS. As a glucose biosensor, the sensitivity can be described by the sequence: GOPMOS > APTOS > TEOS with detection limits down to 44 μM. The sensor lifetime was improved by elimination of ethanol from the hydrolysed oxysilanes by heating in a hot air stream after which APTOS-based sensors showed superior properties to GOPMOS, but with higher detection limit, and were sufficiently stable to be used for over several weeks.