Microbial biosensor for p-nitrophenol using Moraxella sp. Original Research Article

A novel microbial biosensor/electrode for highly selective, sensitive and rapid quantitative determination of p-nitrophenol (PNP) was developed using PNP-degrading organisms immobilized in a membrane on a dissolved oxygen electrode. Moraxella sp. specifically oxidizes PNP while consuming oxygen. A change in oxygen concentration was determined by a Clark oxygen electrode and correlated to the PNP concentration. The sensor signal and response time were optimized with respect to the buffer pH, temperature, time of cell growth and weight of cells immobilized. The best sensitivity and response time were obtained using a sensor constructed with 0.3 mg of cells and operating in pH 7.5, 20 mM phosphate buffer. Using these conditions, the biosensor was used to measure as low as 14 ppb (0.1 μM) of PNP extremely selectively without interference from structurally similar compounds, such as phenol, nitrophenols and chlorophenols. The biosensor had very good storage and multiple use stability when stored in the operating buffer at 4 °C.