Eff ects of Film Thickness and Potential on Response and Interference Suppression of Nitrite Biosensor

Abstract

An amperometric myoglobin-based biosensor was developed for detection of nitrite by entrapping myoglobin (Mb) into an electropolymerized polypyrrole (PPy) fi lm deposited on a platinum (Pt) electrode. In order to optimize the sensor response and minimize the interference caused by a common interfering compound, the effects were investigated of the preparation conditions (fi lm thickness corresponding to an electropolymerization charge of 5–400 mC cm-2) and operating conditions (working potentials of +0.60, +0.65 and +0.70 V) on the response and interference suppression of a nitrite biosensor. The current responses to nitrite and ascorbic acid were examined of the obtained PPy/Mb biosensor. The results showed that as the fi lm thickness increased, the response toward nitrite initially decreased and then slightly increased, while the suppression of interference by ascorbic acid increased. The fi lm thickness substantially affected the interference suppression by ascorbic acid because polypyrrole fi lm possesses a size-exclusion property which can suppress electroactive interferent compounds, such as ascorbic acid, and the size exclusion effect relies considerably on the fi lm thickness. An increase in the diffusion barrier against interference with increased fi lm thickness resulted in the enhanced suppression of ascorbic acid. In addition, the results showed that the working potential had a positive infl uence on the response to nitrite across the range studied. However, all the investigated working potentials had a similar effect on the suppression of ascorbic acid.