Gold nanoparticles for designing of smart colorimetric logic gates operations and scavengers for mercury ions in water

Abstract

A smart colorimetric AND logic gate based on citrate stabilized gold nanoparticles using DM and H₂PO₄⁻ as inputs, which operates in aqueous media with low concentration, is reported. A mechanistic study revealed that the catechol groups of DM interact with the surface of the gold nanoparticles and the amino group of DM cross-linked to H₂PO₄⁻ through hydrogen bonds leading to the aggregation of AuNPs showing a distinct colour change, which is supported by UV-vis study and TEM images. The purple coloured aggregated gold nanoparticles with DM and H₂PO₄⁻ exhibit sharp colour change in the presence of Hg²⁺. On the basis of this observation, a nonimplication logic gate system is demonstrated with Hg²⁺ and (DM + H₂PO₄⁻) as the inputs. In this system, the Hg²⁺ ion is reduced to form Au–Hg amalgam with the aid of citrate anions as the reducing agent and exhibited a colour change from purple to reddish-brown, which is supported by XRD data, TEM images and UV-visible study. An AND logic gate thus developed was used for the quantitative analysis of Hg²⁺ in lake water at low concentration as a test sample, satisfactory results were obtained.