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

This work reports on a colorimetric platform for determination of chromium ions (Cr 3+ ) and mercury ions (Hg 2+ ) using silver nanoparticles (AgNPs) capped with cytosine triphosphate (CTP). The capped AgNPs were synthesized one-step by reduction of AgNO 3 in the presence of CTP. It was found that such AgNPs aggregate in the presence of Cr 3+ . 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 Cr 3+ -induced aggregation of AgNPs, exposure to Hg 2+ 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 Cr 3+ or Hg 2+ , with detection limits of 6.25 μM for Cr 3+ and of 0.125 μM for Hg 2+ , 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 Cr 3+ , and from 96% to 108% for Hg 2+ , which is satisfactory for quantitative assays performed in water samples. Cytosine triphosphate-capped silver nanoparticles (cAgNPs) are shown to represent a viable probe for visual and colorimetric detection of Hg 2+ and Cr 3+ via two different mechanisms: aggregation of cAgNPs in case of Cr 3+ ; and amalgamation of cAgNPs in case of Hg 2+ .