Smartphone Assisted Colourimetric Detection and Quantification of Pb2+ and Hg2+ Ions Using Ag Nanoparticles from Aqueous Medium

Pollution of aquatic bodies with Lead and Mercury is a serious environmental issue, and there exists an unmet need to develop easy and portable detection techniques. Herein, we report a silver nanoparticle (AgNP) based system exhibiting high selectivity and distinct spectrophotometric behaviour towards these metal ions in the aqueous medium. Though many of the metal ions did not influence the characteristic plasmon spectral profile of AgNPs, Mercury caused the disappearance of absorbance at ~400 nm. Consequently, the yellow solution became colourless at around 7.6 ppm of Hg 2+ ions. While the presence of Pb 2+ ions induced a decrease in the initial plasmon intensity with the concomitant emergence of a new red-shifted band above 500 nm. As a result, the colour of the solution turned from yellow to red. These colour changes are found to fall well within the spectral responses of R, G and B filters of the digital camera. By making use of this, an android mobile application was developed for digitizing the colour values and for doing further quantitative analysis. The estimated concentration value by this method was found to be in good match with those obtained from absorbance measurement. The achieved lower detection limits were ~ 0.8 ppm for Hg 2+ and ~ 1.5 ppm for Pb 2+ ions. This illustrates the potential of the proposed combination of smartphone enabled system with AgNPs for easy discrimination and quantification of these two metal ions from the aqueous medium.