Laccases from Pleurotus ostreatus was extracted from the Shaken flask cultures of Pleurotus ostreatus grown at 25 degrees C with continuous agitation (110 rpm.) in baffled 1000 mL Erlenmeyer flasks containing 200 mL medium. The basal GYP medium used for cultures contained 20 g glucose l(-1), 5 g yeast extract l(-1), 5 g peptone from casein l(-1), and 1 g MgSO4.7H(2)O l(-1). The pH was adjusted to 5.0 with H3PO4 before sterilization. The kinetics of oxidation reactions catalyzed by laccases was studied using 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid). The laccases showed lower specific activity and higher activity in nonpolar organic solvents. A biosensor using laccases was constructed for the determination of phenol. The enzyme was extracted from Pleurotus ostreatus and entrapped in agarose-guar gum composite biopolymer matrix. Phenol was determined by direct reduction of biocatalytically liberated quinone species at -0.1 V versus Ag/AgCl (3M KCl). The response was found to be linear and concentration dependent. It has a shelf life of more than 2 months when stored at 4 degrees C. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1358-1365, 2010