Tiopronin protected gold-silver bimetallic nanoclusters for sequential detection of Fe3+ and ascorbic acid in serum

Tiopronin (TPN) protected gold-silver bimetallic nanoclusters (TPN-AuAg NCs) were synthesized in an aqueous medium by a one-pot method. The synthesized TPN-AuAg NCs are spherical with an average diameter of 1.75 ± 0.5 nm and can emit bright fluorescence in the red spectral range (Em = 670 nm). Based on the “on-off-on” process of the nanoclusters' fluorescence, a fluorescent probe for sequential detection of Fe3+ and ascorbic acid (AA) was proposed. After adding Fe3+ ions into the TPN-AuAg NCs solution, a composite Fe3+@TPN-AuAg NCs could be formed. Due to the internal filtering effect (IFE) between Fe3+ and TPN-AuAg NCs, the fluorescence of the nanoclusters was quenched. Subsequently, when AA was continuously added to the fluorescence quenching system, based on the reduction effect of AA on Fe3+ in the complex, the fluorescence of Fe3+@TPN-AuAg NCs could be sensitively turned on. The detection limits of the fluorescence titration measurements calculated using the equation 3σ/k, were 150 nM (Fe3+) and 60 nM (AA), respectively. The proposed method has been successfully applied to detect Fe3+ and AA in human serum samples.