Enhanced enzymatic electrochemical detection of an organophosphate Pesticide: Achieving Wide linearity and femtomolar detection via gold nanoparticles growth within polypyrrole films

Abstract

The indiscriminate use of pesticides in agriculture demands the development of devices capable of monitoring contaminations in food supplies, in the environment and biological fluids. Simplicity, easy handling, high sensitivities, and low limits-of-detection (LOD) and quantification are some of the required properties for these devices. In this work, we evaluated the effect of incorporating gold nanoparticles into indigo carmine-doped polypyrrole during the electropolymerization of films for use as an acetylcholinesterase (AChE) enzyme-based biosensor. As proof of concept, the pesticide methyl parathion was tested towards the inhibition of AChE. The enzyme was immobilized simply by drop-casting a solution, eliminating the need for any prior surface modification. The biosensors were characterized with cyclic voltammetry, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The assays for the detection of methyl parathion with films containing polypyrrole, indigo carmine and AChE (PPy-IC-AChE) presented a sensitivity of 5.7 μA cm^-2 g^-1 mL and a LOD of 12 nmol L^-1 (3.0 ng L^-1) with a linear range from 1.3 x 10^-7 mol L^-1 to 1.0 x 10^-5 mol L^-1. The introduction of gold nanoparticles (AuNP) into the film (PPy-IC-AuNP-AChE) led to remarkable improvements on the overall performance, such as a lower redox potential for the enzymatic reaction, a 145 % increase in sensitivity (14 μA cm^-2 g^-1 mL), a wider detection dynamic range (from 1.3x10^-7 to 1.0x10^-3 mol L^-1), and a very low LOD of 24 fmol L^-1 (64 ag mL^-1). These findings underscore the potential of using AuNPs to improve the enzymatic performance of biosensor devices.

Keywords: Acetylcholinesterase; Enzymatic biosensor; Methyl parathion; Nanoparticle-enhanced biosensing; Pesticide detection; Polypyrrole nanocomposite.