▎ 摘　　要

Graphene oxide nanoparticles (G@NP) were synthesized from graphite powder of lead pencil and characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). A mixture of G@NPs and polypyrrole (PPy) was electropolymerized onto gold (Au) electrode followed by electrodeposition of a mixture of polyaniline (PANI) and chitosan (CHIT) onto G@NPs/PPy/Au to construct CHIT/PANI/G@NPs/PPy/Au electrode. An oxalate oxidase (OXO) purified from strawberry fruits was immobilized on to this modified Au electrode through chitosan. The enzyme electrode (OXO/CHIT/PANI/G@NPs/PPy/Au electrode) was characterized by cyclic voltammetry (CV), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrophotometry and electrochemical impedance spectroscopy (EIS) at different stages of its construction. The OXO/G@NPs/PPy/PANI/CHIT/Au electrode as working electrode, Ag/AgCl as reference electrode and Pt wire as auxiliary electrode were connected through a potentiostat to fabricate an amperometric oxalate biosensor. The biosensor exhibited optimum response within 3s at pH 5.5, 35 degrees C with a linearity, between 1 and 400 mu M for oxalic acid and a detection limit of 1 mu M. Apparent Michaelis-Menten constant (K-m) for oxalate was 12.5 mu M while I-max was 0.008 mA. The optimized biosensor measured oxalate level in urine and plasma collected from apparently healthy persons and urinary stone formers. (C) 2013 Elsevier B.V. All rights reserved.