Highly sensitive and selective colorimetric detection of Pb(ii) ions using Michelia tonkinensis seed extract capped gold nanoparticles

In this study, gold nanoparticles (AuNPs) were synthesized via a green and environmentally-friendly approach and applied as a colorimetric probe for detecting Pb(2+) ions in aqueous solution. Instead of toxic chemicals, Michelia tonkinensis (MT) seed extract was used for reducing Au(3+) and stabilizing the formed AuNPs. The synthesis conditions, including temperature, reaction time, and Au(3+) ion concentration, were optimized at 90 °C, 40 min, and 1.25 mM, respectively. The physicochemical properties of the produced MT-AuNPs were assessed by means of transmission electron microscopy, X-ray diffraction, field emission scanning electron microscopy, dynamic light scattering, and Fourier-transform infrared spectroscopy. The characterization results revealed that the MT-AuNPs exhibited a spherical shape with a size of about 15 nm capped by an organic layer. The colorimetric assay based on MT-AuNPs showed excellent sensitivity and selectivity toward Pb(2+) ions with the limit of detection value of 0.03 μM and the limit of quantification of 0.09 μM in the linear range of 50–500 μM. The recoveries of inter-day and intra-day tests were 97.84–102.08% and 98.78–102.34%, respectively. The MT-AuNPs probe also demonstrated good and reproducible recoveries (98.71–101.01%) in analyzing Pb(2+) in drinking water samples, indicating satisfactory practicability and operability of the proposed method.