Oligonucleotide-functionalized silver nanoparticle extraction and laser-induced fluorescence for ultrasensitive detection of mercury(II) ion.

This study describes the development of a simple, sensitive, and selective detection system for Hg(2+) ion by combining nanoparticle extraction, fluorescent dye labeling, and flow injection analysis (FIA) detection. Repeats of 33 thymine nucleotides-functionalized silver nanoparticles (T(33)-AgNPs) specifically capture Hg(2+) from aqueous solution through the coordination between T(33) and Hg(2+). Meanwhile, Hg(2+) ion drives a T(33) conformational change from a random coil to a folded structure. The T(33)-Hg(2+)complexes adsorbed on the NP surface were collected from the initial sample by centrifugation, and they were then detached from the NP surface by addition of H(2)O(2). The T(33)-Hg(2+) complexes preferentially bind to SYBR Green I (SG), enhancing the SG fluorescence. By contrast, SG fluoresces only weakly in the presence of T(33) alone. The extraction efficiency of Hg(2+) was highly dependent on polythymine length, the concentration of T(33)-AgNPs, and the incubaton time of T(33)-AgNPs with Hg(2+). Under optimal extraction and labeling conditions, FIA detection showed the limit of detection (at a signal-to-noise ratio of three) for Hg(2+)of 3 pM. The selectivity of our analytical system is more than 1000-fold for Hg(2+) over any metal ions. We validated the applicability of this system for the determination of Hg(2+) concentrations in tap water.