Construction of a chitosan/polyaniline/graphene oxide nanoparticles/polypyrrole/Au electrode for amperometric determination of urinary/plasma oxalate

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 auxillary electrode were connected through a potentiostat to fabricate an amperometric oxalate biosensor. The biosensor exhibited optimum response within 3 s at pH 5.5, 35 °C with a linearity, between 1 and 400 μM for oxalic acid and a detection limit of 1 μM. Apparent Michaelis–Menten constant (Km) for oxalate was 12.5 μM while Imax was 0.008 mA. The optimized biosensor measured oxalate level in urine and plasma collected from apparently healthy persons and urinary stone formers.