A rapid colorimetric dual sensor for the detection of mercury and lead ions in water using cysteine capped silver nanoparticles
Vimala Rani Samuel, K. Jagajjanani Rao
Abstract
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.