Ultrasensitive, highly specific, colorimetric recognition of sulfide ions [S2−] in aqueous media: applications to environmental analysis

Abstract

Herein, we have demonstrated a simple, ultrasensitive and highly specific colorimetric assay for the detection of sulfide ions (S²⁻) based on the aggregation of nanoparticles via electrostatic interaction of a surface capped gold nanoparticles with S²⁻ in aqueous media. Cetylpyridinium bromide capped gold nanoparticles (CPB-AuNPs) were synthesized by a borohydride chemical reduction method and further characterized using UV-visible and fluorescence spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential measurements. The change in color from red to purple immediately after the addition of S²⁻ in the solution of CPB-AuNPs was first monitored by the naked eye and then by UV-vis spectroscopy to construct calibration plot for practical applications. Under the optimized circumstances, a plot of [(A₀ − A)/A] versus the concentrations of S²⁻ was linear over the range of 0.01–1.0 μg mL⁻¹ with a correlation coefficient of 0.9952. The developed method also shows excellent selectivity towards S²⁻ by a factor of 20-fold or more relative to sixteen interfering ions that were tested. The probe offers a low limit of detection (LOD) up to 0.0013 μg mL⁻¹ (40.6 nM), which is much lower (about 400-fold) than the maximum level (0.5 μg mL⁻¹ or 15 625 nM) of S²⁻ in drinking water permitted by the World Health Organization (WHO). Moreover, our results demonstrate the practical applicability of the probe for S²⁻ sensing in environmental water samples without pretreatment or use of a masking agent. Therefore, the proposed scheme could be a good alternative means for onsite and real time screening of S²⁻.