The development of unmodified silver nanoparticles (AgNPs) as colorimetric Hg(ii) sensor for a new approach to sensitive and high sample throughput determination of hg(ii) under high influence of ionic matrix

In this thesis presents an unmodified silver nanoparticles (AgNPs) as colorimetric sensor prepared by green and facile method for determination of Hg(II) ions in aqueous samples which is developed using UV-Vis spectrophotometry Abrupt change in absorbance of the AgNPs is observed, which progressively decreased and slightly shifted to the blue wavelength as the concentration of Hg(II) increased. It appears that the AgNPs were oxidized by Hg(II), resulting in disintegration of the AgNPs and Hg(0). Deposition of Hg(0) on the surface of AgNPs also occurred, resulting in amalgam of particles of mercury (HG-Ag). Interestingly, the developed approach showed a significant enhancement in the Hg(II) analytical sensitivity when formic acid was doped onto the AgNPs, with the linearity range of 0.01-10 mg L-1 (r2=0.999) providing the quantitative detection limit of 0.007 mg L-1 (3SD blank/slope of the calibration curve). Greater selectivity toward Hg(II) over other ions and color dyes was also observed, likely a result of stabilization by polyvinylpyrrolidone (PVP), which kept the AgNPs well-stabilized and dispersed in the bulk aqueous environment making them resistant to ionic matrix. Under using a 96-well microplate and a smartphone equipped with homemade application as a colorimetric analyzer under controlled lighting, high sample throughput (128 sample h-1) was achieved, establishing its potential for practical analysis. The percentage recoveries of spiked aqueous samples obtained from the microplate-based system were in acceptable range, in agreement with the values obtained from the UV-Vis spectrophotometry-based system. The proposed colorimetric sensor has been demonstrated to provide a rapid, simple, sensitive and selective detection of Hg(II) ions in various aqueous samples.