Amperometric determination of lysine using a lysine oxidase biosensor based on rigid-conducting composites

In this study, amperometric biosensors based on rigid conducting composites are developed for the determination of lysine. These lysine biosensors con sist of chemically immobilized lysine oxidase membranes attached to either graphite-methacrylate or peroxidase-modified graphite-methacrylate electrod es. The enzymatic degradation of lysine releases hydrogen peroxide, which i s the basis of the amperometric detection. The direct oxidation of hydrogen peroxide is monitored at + 1000 mV with a graphite-methacrylate electrode, while with the peroxidase-modified electrode reductive detection is perfor med. In addition, for the peroxidase-modified biocomposite electrode, both direct electron transfer and hydroquinone-mediated detection are studied. F or the lysine biosensor based on the hydroquinone-mediated peroxidase bioco mposite, the linear range is up to 1.6 x 10(-4) M, the sensitivity 11300 mu A/M, the repeatability 1.8%, the detection limit 8.2 x 10(-7) M and the re sponse time t(95%) is 42 s. The proposed biosensors are used to determine l ysine in pharmaceutical samples. Results are consistent with those obtained with the standard method. (C) 1999 Elsevier Science S.A. All rights reserv ed.