Biocomposite of cobalt phthalocyanine and lactate oxidase for lactate biosensing with MnO2 nanoparticles as an eliminator of ascorbic acid interference

We report on the formation of colloidal biocomposites resulting from the electrostatic self-assembly of negatively charged lactate oxidase (LOD) and oppositely charged nanoscaled cobalt phthalocyanine (NanoCoPc) colloid under enzyme-friendly conditions. The biocomposites were further used to fabricate lactate biosensors due to their excellent film-forming ability and strong adsorbability on the surface of glassy carbon electrode. The electrochemical assays of such films revealed a large capacity of NanoCoPc for the retention of LOD. Here, NanoCoPc colloid was not only used as carriers for immobilization of LOD, but also displayed intrinsic electrocatalytic activity for the oxidation of H2O2, a product of enzymatic reaction. A chitosan film containing MnO2 nanoparticles was further electrodeposited as an external layer, which could effectively eliminate the interference from ascorbic acid. Under optimal conditions, the biosensor showed a wide linear response to lactate in the range of 0.020-4.0 mM, with high sensitivity (3.98 mu A cm(-2) mM(-1)), as well as good reproducibility and long-term stability. The biosensor has been used for the determination of lactate in real samples with an acceptable accuracy. (c) 2005 Elsevier B.V. All rights reserved.