Colorimetric Detection of Mercuric Ion (Hg²⁺) in Aqueous Media Using DNA-Functionalized Gold Nanoparticles

Mercury is a widespread pollutant with distinct toxicological profiles, and it exists in a variety of different forms (metallic, ionic, and as part of organic and inorganic salts and complexes). Solvated mercuric ion (Hg²⁺), one of the most stable inorganic forms of mercury [1], is a caustic and carcinogenic material with high cellular toxicity [2]. 1552The most common organic source of mercury, methyl mercury, can accumulate in the human body through the food chain and cause serious and permanent damage to the brain with both acute and chronic toxicity [3-5]. Methyl mercury is generated by microbial biomethylation in aquatic sediments from water-soluble mercuric ion (Hg²⁺) [4]. Therefore, routine detection of Hg²⁺ is central to the environmental monitoring of rivers and larger bodies of water and for evaluating the safety of aquatically derived food supplies [5, 6]. Several methods for the detection of Hg²⁺, based upon organic fluorophores [7] or chromophores [8], semiconductor nanocrystals [9], cyclic voltammetry [10], polymeric materials [11], proteins [12], and microcantilevers [13], have been developed. Colorimetric methods, in particular, are extremely attractive because they can be easily read out with the naked eye, in some cases at the point of use. Although there are now several chromophoric colorimetric sensors for Hg²⁺ [8], all of them are either limited with respect to sensitivity (current limit of detection ~1 gm) and selectivity, kinetically unstable, or incompatible with aqueous environments.