A silicon-based biosensor chip consisting of an array of amperometric enzyme sensors has been developed for monitoring the concentration of glutamate and glutamine in cell-culture fermentation processes. The glutamate sensor was constructed by immobilising glutamate oxidase, while the glutamine sensor by sequential coupling of glutaminase and glutamate oxidase. The enzymes were immobilised by means of cross-linking with glutaraldehyde on the surface of the patterned platinum thin-film electrodes. The developed biosensors have been electrochemically characterised in solutions with different concentrations of glutamate and glutamine in terms of sensitivity, response time, linear working range and lifetime. A high sensitivity of 96 nA/mM and 100 nA/mM was registered for the glutamate and glutamine sensors, respectively. The preliminary experiments in cell-culture medium have shown a good correlation between the glutamine and glutamate concentrations measured with the biosensor chip and the commercially available biochemistry analyser. The obtained results demonstrate the feasibility of the realised biosensor chip for monitoring the glutamine and glutamate concentrations in fermentation processes. (C) 2011 Elsevier Ltd. All rights reserved.