Desenvolvimento de biossensor potenciométrico em eletrodos de grafite modificado com aminofenóis para determinação de diclorvós em alimentos de origem vegetal

Abstract

In this work a potentiometric biosensor based of enzyme acetylcholinesterase (AChE) was developed. As transducer, graphite electrodes, and graphite modified with film of poly (2-aminophenol), poly (3- aminophenol) and poly(4-aminophenol) were used. The ability of these electrodes in the transduction in function of the acetic acid concentration was evaluated in a flow system, and the electrodes of graphite and graphite modified with poly(4-AMP) showed promising analytical characteristics for potentiometric detection. The enzyme AChE was immobilized by cross-linking on the surfaces of graphite and graphite / poly(4-AMP). Figures of merit (detection limit, quantification limit, linear response range, linearity, sensitivity, washing time, velocity of response) for the two biosensors were measured in function of the substrate concentration. The response of the biosensor (graphite/poly(4-AMP)/AChE) was optimized for different experimental conditions (pH, phosphate buffer concentration, substrate concentration, flow rate and injection volume). Studies by electrochemical impedance spectroscopy (EIS), cyclic voltammetry and AFM analysis for graphite electrodes, with poly (4-AMP) and graphite / poly (4-AMP) / AChE changes were made to confirm the modifications in the electrodes. The percentage of inhibition of AChE enzyme inhibitor has been evaluated using the dichlorvós in different concentrations and time of incubation. The enzyme activity immobilized vs. concentration of the substrate was optimized to propose a method without stopped flow to a maximum of inhibition. The detection and quantification limits of 0.8 μmol L-1 (0.18 mgL-1) and 2.4 μmol L-1 (0.53 mg L-1) for dichlorvos, respectively, were obtained without stopped flow. Recoveries in potato sample showed that the method was sufficiently accurate for the levels of dichlorvos evaluated at a confidence interval of 95%. Coefficient of variation and coefficient of variation global validated the precision of the method. These results were comparable to values of precision obtained by gas chromatography with electron-capture detection and mass spectrometry. The results showed that the graphite electrode/poly(4-AMP) was biocompatible for imobilization of the enzyme AChE and the biosensor can be used as detector coupled with flow injection analysis for determination of waste pesticides inhibitors of AChE in foods of vegetal origin.