Development of an electrochemical sulfite biosensor by immobilization of sulfite oxidase on conducting polyaniline film

In this work, a biosensor was developed for the determination of sulfite. The bioelectrochemical response of the enzyme-modified electrode based on electrochemical incorporation of sulfite oxidase into polyaniline aluminum modified electrode was investigated. Electropolymerization of polyaniline and simultaneous immobilization of sulfite oxidase on the aluminum were performed in an aqueous solution containing sulfite oxidase. The sulfite biosensor constructed by cycling the potential scan between +1.2 and −0.5 V vs. saturated calomel electrode (SCE) that showed a sensitive response to sulfite with a linear calibration graph in the concentration ranges of 0.006–5 mM sulfite and detection limit 0.002 mM sulfite (S/N = 3). The obtained results from the stability tests of the biosensor show that the sulfite biosensor can be used for two different applications, for immediate usage and long term usage. Also, the bioelectrochemical response of the enzyme-modified electrode as a sulfite biosensor was evaluated at different experimental conditions. The optimum pH when using phosphate buffer and temperature were 8.5 and 35 °C, respectively. Finally, the apparent Michaelis–Menten constant was determined which has value of 0.365 mM which is really close to the magnitude of the Michaelis–Menten constant of free sulfite oxidase that shows the enzyme was not chemically modified and has its usual kinetic reaction.