Smartphone Motivated Highly Selective and Sensitive Colorimetric Detection of Hg2+ through Limonin Derived Silver Nanoparticles

Mercury (Hg²⁺) as environmental pollutant is a widespread concern due to its cytotoxic effect in humans and animals and needs to be monitored through cost effective methods based on naked-eye detection. Herein, in this study, we extracted and isolated the limonin (LMN) via a facile procedure and then employed it as capping agent for the synthesis of silver nanoparticles (LMN-AgNPs) as a first report. LMN-AgNPs were characterized through Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), Dynamic Light Scattering (DLS), Zeta Potential Analyzer (ZPA) and Fourier Transform Infrared (FTIR) spectroscopy. As-formed LMN-AgNPs were recognized as extremely selective and highly sensitive colorimetric sensor for Hg²⁺ with potential analytical application. The developed sensor showed an outstanding linear correlation with the concentration of Hg²⁺ in the range of 0.002 − 55 µM via a color change from deep yellow to transparent showing hypsochromic-hypochromic shift with the limit of detection (LOD) and the limit of quantification (LOQ) as low as 0.21 nM and 0.7 nM respectively. The sensor was further allied with smartphone for immediate and on-site quantification of Hg²⁺. The LOD and LOQ of 0.42 µM and 1.4 µM was true for smartphone based sensing in the range of 7.5–55 µM Hg²⁺. The detection of Hg²⁺ was not disrupted by the presence of other metals in either of mentioned cases. The practical applicability of the proposed Hg²⁺ sensor was tested using spectrophotometric and smartphone based approaches in human serum and urine as well as in tap water samples with acceptable ranges of recovery. As-developed sensor can work as a potential candidate for monitoring of Hg²⁺ pollution in diverse fields of studies.