A rapid colorimetric dual sensor for the detection of mercury and lead ions in water using cysteine capped silver nanoparticles

Thiol groups containing amino acids like cystine and l-cysteine help in the chelation of poisonous heavy metals in biological systems therein making them eliminated easily in urine. Based on this phenomenon, cysteine-coated silver nanoparticles could be helpful as potential label-free sensors systems for detecting heavy metals. In this study, the benefit of using silver nanoparticles with cysteine capping (Cys-AgNPs) for colorimetric detection of individual and simultaneous sensing of Lead(Pb2+) and Mercury( Hg2+) in water samples was reported. Cys-AgNPs were characterized using spectroscopy, microscopy, X-ray diffractometer analysis and the photophysical properties of the particles towards Hg2+ and Pb2+ ions were investigated through absorption spectroscopy and colorimetric tests. Upon exposure of Hg2+ ions to Cys-AgNPs, a hypsochromic shift in the surface plasmon resonance (SPR) band with decreased intensity was detected. In contrast, it was a bathochromic shift with an increase in absorbance intensity observed with Pb2+ ions. Cys-AgNPs are highly sensitive toward Hg2+ and Pb2+ ions individually with clear color changes in the solution visible to the naked eye. The limit of detection (LOD) was found to be 45.39 × 10−9 M (for Hg2+ ions) and 49.39 × 10−9 M (for Pb2+ ions). Furthermore, dual ion sensing ability was also assessed by Cys-AgNPs by varying Hg2+ and Pb2+ ions individually in water samples. The LOD for constant Hg2+ and varying Pb2+ was found to be 43 × 10−9 M while it is 37.95 × 10−9 M for constant Pb2+ and varying Hg2+. These results determine that the Cys-AgNPs system has potential application as a colorimetric sensor for the detection of individual or mixed Hg2+ and Pb2+ ions in water samples quickly. [Display omitted]