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 amperometric screen-printed glucose biosensors for food analysis by using two procedures for Prussian Blue (PB) deposition and different membranes for enzymatic immobilisation. The comparison between the screen-printed electrodes modified with PB by electrochemical and chemical deposition showed higher analytical performance (detection limit of 1 mu M, linear range from 0.5 to 500 mu M and a sensitivity of 823 mu A mM(-1) cm(-2)) when the latter was employed. Then, the immobilisation of glucose oxidase (GOD) by silica sol-gel and polyvinyl alcohol (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 negligible interference from ascorbic acid when the Nafion membrane 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.