A label-free oligonucleotide based thioflavin-T fluorescent switch for Ag+ detection with low background emission.

A novel fluorescent Ag(+) sensor was developed based on the label-free silver (I) specific oligonucleotide (SSO) and Thioflavine T (ThT) monomer-excimer switch. C-rich SSO which contain C-C mismatched base pairs can selectively bind to Ag(+) ions and the formed duplexes which constructed by C-Ag(+)-C structure are thermally stabilized without largely altering the double helical structure. ThT give very weak fluorescent in bulk solution and/or in the presence of SSO. However ThT shows high fluorescence in the presence of SSO and Ag(+) at the same time mainly because ThT excimer, which has the high quantum yield, formed and stabilized in the minor or major groove. Based on the discovery, we developed the novel Ag(+) sensor. Under the optimum condition, the selectivity of this system for Ag(+) over other metal ions in aqueous solution is remarkably high, and Ag(+) can be quantified over the dynamic range of 30-450 nM, with a limit of detection of ~16 nM and a linear correlation coefficient of 0.995.