Free and sol–gel immobilized alkaline phosphatase-based biosensor for the determination of pesticides and inorganic compounds

Abstract

Alkaline-phosphatase (ALP) catalyses the hydrolysis of 1-naphthyl phosphate to fluorescent 1-naphthol ( λ ex=346 nm, λ em=463 nm). This enzymatic reaction was investigated in presence of inhibitors: organochlorine (tetradifon), carbamate (metham-sodium) and organophosphorus pesticides (fenitrothion), heavy metal (Ag +) and CN −. The fluorescent signal, which is inversely dependent on the inhibitor concentration, is related to the amount of the inhibitor. Detection limits between 4.1 μM for tetradifon and 91.2 μM for metham-sodium were found. The relative standard deviation (R.S.D.) was between 2.6 and 6.2%. Sol–gel matrices derived from tetramethyl orthosilicate were doped with ALP using microencapsulation. The response of the biosensor based ALP sol–gel encapsulated to 1-naphthyl phosphate was reproducible (R.S.D.=6.6%). Inhibition plots obtained for test pesticides (metham-sodium and tetradifon) display linear calibration in the ranges 194–774 μM and 3.5–28 μM, detection limits of 4.9 and 292.3 μM and R.S.D. of 3.9 and 7.3% for metham-sodium and tetradifon, respectively. The results show that the system is able to detect class compounds such as pesticides and inorganic compounds.