A Novel Fluorescent Biosensor for Detection of Silver Ions Based on Upconversion Nanoparticles.

In this paper, we report a simple and sensitive fluorescent biosensor for the quantitative analysis of silver ions (Ag+) by using NaYF4:Yb3+, Tm3+ upconversion nanoparticles (UCNPs). Ag+ could oxidize o-phenylenediamine (OPD) to the oxidized OPD (oxOPD) directly. The fluorescence of UCNPs can be significantly quenched by oxOPD through inner filter effects (IFE). Under the optimized conditions, the Ag+ concentration is proportional to the changes of the fluorescence intensity of UCNPs. The proposed method shows high selectivity and Ag+ could be quantitatively detected in the range of 0 to 0.5 mM with a low detection limit of 33 nM for Ag+. The selectivity and sensitivity of the detection can also be satisfactory. More importantly, this method has potential in practical application to detect Ag+ in real samples without interference.