Glutathione protected bimetallic gold-platinum nanoclusters with near-infrared emission for ratiometric determination of silver ions

A controlled method to prepare glutathione-protected bimetallic gold-platinum nanoclusters (Au-PtNCs) has been established. The Au-PtNCs show either strong red (625 nm) or near-infrared (NIR, 805 nm) emission. Further characterizations indicated that the average particle size grows from 1.42 to 1.78 nm, the larger particles being responsible for the redshift of emission. The NIR emitted Au-PtNCs are applied as a novel ratiometric probe of Ag(I), which induces a new emission peak at ~635 nm and quenches the initial emission gradually. The determination shows very high selectivity toward Ag(I) among other metal ions. A limit of determination (10 nM) and the linear range (0.10 to 15 μM) are achieved, which is much lower than the EPA mandate of 0.46 μM for Ag(I) in drinking water. The response mechanism is attributed to the fact that the added Ag(I) has been reduced by the core of Au-PtNCs and deposited on the surface, which induces new fluorescence emission around 635 nm. In addition, the ratiometric method is feasible for Ag(I) determination in serum serum with good recovery (between 98.3% and 102.0%, n = 3), showing very high application potential. The present study provides a controlled method to prepare Au-PtNCs with strong red and NIR emission and supplies a novel NIR ratiometric probe of Ag(I). Graphical abstract: