Reagentless mediated biosensors based on polyelectrolyte and sol–gel derived silica matrix

A new approach to assemble reagentless amperometric biosensors is presented. The mediators (ferrocene and its derivatives) and the enzyme (glucose oxidase, GOD) are co-immobilized in a sol–gel derived silica (SGS) matrix containing polyelectrolyte (PE) to produce highly stable and sensitive glucose sensors on different base electrodes. The effective immobilization of the enzyme and the mediators comes from the co-operative entrapment by the PE and the three-dimensional interpenetrating network of the (SGS) membrane. The featured PE–SGS membrane provides a favorable environment and functional ligand ‘locking’ mechanism for the immobilized enzyme to remain in its active conformation for high biological activity, and shuttles electrons efficiently from electrode to enzyme via the immobilized mediator without mediator leaching even after long periods of operation. Important sensing parameters such as the catalytic rate constant (k), the apparent Michaelis–Menten constant (KMapp) and the substrate specificity factor (k/KMapp) are evaluated and discussed. The fabricated biosensors demonstrated a useful working range up to 80 mM with fast response time less than 10 s, and a detection limit around 0.3 mM.