A method is described for construction of an amperometric xanthine biosensor based on covalent Immobilization of xanthine oxidase (XOD) onto citrate capped silver nanoparticles deposited on Au electrode surface through cysteine self assembled monolayers (SAM). The biosensor showed optimum response within 5s at pH 7.0 and 35 degrees C, when polarized at 0.5 V vs. Ag/AgCl. The linear working range of biosensor for xanthine was from 2 to 16 mu M, with a detection limit of 0.15 mu M and sensitivity of 0.17 mA/mu M/cm(2). The mean analytical recovery of exogenously added xanthine in fish meat extract (5 g/l and 10 g/l) was 96.2 +/- 2.3% and 95.2 +/- 3.4%, respectively. Within and between batches coefficients of variation were <2.6% and <3.4%, respectively. The biosensor measured xanthine in fish, chicken, pork, and beef meat. The enzyme electrode lost 20% of its initial activity after its regular 180 uses over a period of 60 days, when stored at 4 degrees C in dry state. (C) 2013 Elsevier Ltd. All rights reserved.