Cytosine triphosphate-capped silver nanoparticles as a platform for visual and colorimetric determination of mercury(II) and chromium(III)

Abstract

This work reports on a colorimetric platform for determination of chromium ions (Cr3+) and mercury ions (Hg2+) using silver nanoparticles (AgNPs) capped with cytosine triphosphate (CTP). The capped AgNPs were synthesized one-step by reduction of AgNO3 in the presence of CTP. It was found that such AgNPs aggregate in the presence of Cr3+. This results in a decrease in the intensity of the surface plasmon resonance (SPR) band at 390 nm and the formation of a new red-shifted band at 510 nm, and consequently a color change from yellow to red. Different from the Cr3+-induced aggregation of AgNPs, exposure to Hg2+ causes the formation of a mercury layer around the surface of the AgNPs. This, in turn, causes the SPR absorption of the AgNPs to decrease and to undergo a slight blue shift, and this results in a fading of the yellow color. The findings are the basis of developing a new method for quantification of either Cr3+ or Hg2+, with detection limits of 6.25 μM for Cr3+ and of 0.125 μM for Hg2+, respectively. The method was applied to the determination of the two ions in spiked drinking water and lake water samples, and recoveries ranged from 94.5% to 101.3% for Cr3+, and from 96% to 108% for Hg2+, which is satisfactory for quantitative assays performed in water samples.