Functionalization of 6-mercaptopyridine-3-carboxylic acid on gold nanoparticles for selective and sensitive detection of heavy metal cadmium

Abstract

Cadmium (Cd⁺²) is a hazardous heavy metal that can cause serious health problems, including cancer. Because of this, the World health organization (WHO) fixed the maximum allowed limit of Cd⁺² in drinking water or industrial wastewater is 3.0 µgL⁻¹. To accurately detect even lower concentration of Cd⁺², a reliable and easy-to-use method was developed by our group. Here in this work, simple and visual detection was proposed to detect Cd²⁺ ions by using 6-Mercaptopyridine-3-carboxylic acid functionalized gold nanoparticles (MPyC-AuNPs). The prepared MPyC-AuNPs were characterized by UV–visible spectrometry, dynamic light scattering (DLS), zeta potential and Fourier transform infrared spectroscopy (FT-IR). The characteristic surface plasmon resonance (SPR) peak of MPyC-AuNPs was observed at 524 nm, and the aggregation of MPyC-AuNPs leads to spectral change from 524 nm to 677 nm. The aggregation is due to the formation of the metal ligand coordination between MPyC-AuNPs and Cd²⁺ ions. Moreover, MPyC-AuNPs based sensor is highly selective for the detection of Cd²⁺ and giving response only for Cd²⁺ among tested metal ions. Under the optimal conditions, a good linear relationship (R² = 0.9956) was observed between the ratio of the extinction at 680 nm to that at 524 nm and the concentration of Cd²⁺ over the range of 1 µM - 100 µM. The detection limit was found to be 5.4 × 10⁻⁷µM, which is equal to 0.0607µgL⁻¹ lesser than the allowed limit by WHO. Moreover, the developed sensor was capable to detect Cd²⁺ from water samples with good recovery and lesser relative standard deviation. Thus MPyC-AuNPs proven as efficient sensors for the on-site monitoring of Cd²⁺ in water (tap, river and canal) samples.