Magnified fluorescence detection of silver(I) ion in aqueous solutions by using nano-graphite-DNA hybrid and DNase I

This paper describes a novel approach utilizing nano-graphite-DNA hybrid and DNase I for the amplified detection of silver(I) ion in aqueous solutions for the first time. Nano-graphite can effectively quench the fluorescence of dye-labeled cytosine-rich single-stranded DNA due to its strong π-π stacking interactions; however, in the presence of Ag+, C-Ag+-C coordination induces the probe to fold into a hairpin structure, which does not adsorb on the surface of nano-graphite and thus retains the dye fluorescence. Meanwhile, the hairpin structure can be cleaved by DNase I, and in such case Ag+ is delivered from the complex. The released Ag+ then binds other dye-labeled single-stranded DNA on the nano-graphite surface, and touches off another target recycling, resulting in the successive release of dye-labeled single-stranded DNA from the nano-graphite, which leads to significant amplification of the signal. The present magnification sensing system exhibits high sensitivity toward Ag+ with a limit of detection of 0.3 nM (S/N=3), which is much lower than the standard for Ag+ in drinking water recommended by the Environmental Protection Agency (EPA). The selectivity of the sensor for Ag+ against other biologically and environmentally related metal ions is outstanding due to the high specificity of C-Ag+-C formation. Moreover, the sensing system is used for the determination of Ag+ in river water samples with satisfying results. The proposed assay is simple, cost-effective, and might open the door for the development of new assays for other metal ions or biomolecules.