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 (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.

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Graphical abstract Cytosine triphosphate-capped silver nanoparticles (cAgNPs) are shown to represent a viable probe for visual and colorimetric detection of Hg²⁺ and Cr³⁺ via two different mechanisms: aggregation of cAgNPs in case of Cr³⁺; and amalgamation of cAgNPs in case of Hg²⁺.