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 Hg2+ ion by combining nanoparticle extraction, fluorescent dye labeling, and flow injection analysis (FIA) detection. Repeats of 33 thymine nucleotides-functionalized silver nanoparticles (T33–AgNPs) specifically capture Hg2+ from aqueous solution through the coordination between T33 and Hg2+. Meanwhile, Hg2+ ion drives a T33 conformational change from a random coil to a folded structure. The T33–Hg2+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 H2O2. The T33–Hg2+ complexes preferentially bind to SYBR Green I (SG), enhancing the SG fluorescence. By contrast, SG fluoresces only weakly in the presence of T33 alone. The extraction efficiency of Hg2+ was highly dependent on polythymine length, the concentration of T33–AgNPs, and the incubaton time of T33–AgNPs with Hg2+. Under optimal extraction and labeling conditions, FIA detection showed the limit of detection (at a signal-to-noise ratio of three) for Hg2+of 3 pM. The selectivity of our analytical system is more than 1000-fold for Hg2+ over any metal ions. We validated the applicability of this system for the determination of Hg2+ concentrations in tap water.

► Polythymine can be used for extracting and detecting Hg2+.
► This is first example of the quantification of Hg2+ in tap water using polythymine.
► This method provided the lowest LOD (3 pM) for Hg2+ compared to other sensors.
► The selectivity of this method provided >1000-fold selectivity toward Hg2+.
► The sensitivity of this method is compared to that of ICP-MS.