Optimisation of Glucose Biosensors Based on Sol–Gel Entrapment and Prussian Blue-Modified Screen-Printed Electrodes for Real Food Analysis

In this study, we report the construction of ampero- metric screen-printed glucose biosensors for food analysis by using two procedures for Prussian Blue (PB) deposition and different membranes for enzymatic immobilisation. The com- parison between the screen-printed electrodes modified with PB by electrochemical and chemical deposition showed higher analytical performance (detection limit of 1 μM, linear range from 0.5 to 500 μM and a sensitivity of 823 μ Am M �1 cm �2 ) when the latter was employed. Then, the immobilisation of glucose oxidase (GOD) by silica sol-geland polyvinylalcohol (PVA) hydrogel was performed on electrochemically modified PB electrodes. The electrochemical response of two glucose biosensors was evaluated by flow injection analysis. Biosensors constructed by silica sol-gel entrapment showed a wider linear range (0.005-1 mM) and a detection limit (0.02 mM) that was 10-fold lower than using entrapped GOD in PVA. The selected glucose biosensor showed negli- gible interference from ascorbic acid when the Nafion mem- brane was used to cover the PB-modified electrode surface. Additionally, it exhibited an operating lifetime of 8 h under continuous glucose injections ranging from 0.01 to 2 mM. Finally, the biosensor was applied for specific determination of glucose in red and white wines, juices and dried fruit.