Polycation-stabilized PDADMAC-gold nanoparticles as a highly sensitive colorimetric sensor for the detection of the chlorpyrifos pesticide

Herein, we report the preparation of positively charged and stable gold nanoparticles (AuNPs) using a strong polycation, polydiallyldimethylammonium chloride (PDADMAC), as a stabilizing agent, for the colorimetric detection of a typical organophosphorus pesticide, chlorpyrifos (CPF). As deduced from zeta potentials, beside strong interaction of sulfur atom in CPF molecule with AuNPs, the hydrophobic interaction of CPF with PDADMAC outer shell significantly enhanced the sensitivity of the method, with an ultralow detection limit down to 2.28 ppb, which satisfies stringent requirement for maximum residue limit allowed by the United State Environmental Protection Agency (EPA) in agricultural products. In the presence of CPF, the PDADMAC-AuNP solution gave a linear increase of maximum absorption wavelength with CPF concentrations. Under the optimum conditions of pH 5, incubation time 25 min, and 3 × 10−3 M Na2SO4, this method achieved a wide linear range from 2.5 × 10−8 to 10−6 M, a low limit of detection (LOD) of 6.5 × 10−9 M (2.28 ppb), and high precision (RSD < 5%). High selectivity for CPF over other pesticides is also demonstrated. The developed sensor can be applied to detect CPF in various real samples such as vegetables or environmental water samples.