"Turn-Off-On" Fluorescence Switching of Ascorbic Acid-Reductive Silver Nanoclusters: a Sensor for Ascorbic Acid and Arginine in Biological Fluids.

In this report, a novel one-step chemical reduction method was reported for synthesis of water-soluble and stable fluorescent glutathione-templated silver nanocluster (GSH-Ag NCs) with ascorbic acid as an environmental-friendly reducing agent. On the basis of an oxidoreduction-induced fluorescence quenching mechanism, the prepared GSH-Ag NCs found to act as a cheap, non-toxic and highly sensitive "turn-off" fluorophore for ascorbic acid (AA). Furthermore, the fluorescence of the fluorophore/AA system could be recovered through addition of arginine (Arg), which made the system function as a highly selective "turn-on" sensor for arginine. Therefore, a "turn-off-on" switch sensor was proposed for detection of AA and Arg. Under optimized conditions, the probe gives a fluorescent response that is linear in the 2-300 μM concentration range of AA, with a detection limit of 0.1 μM. The probe for Arg, in turn, has a linear range in the 10-180 μM concentration range, and the limit of detection is 0.5 μM. In addition, the developed method showed great accuracy when employed to detect AA and Arg in human urine and serum, which shows its great potential in biological molecular recognition applications.