Ratiometric fluorescence detection of dopamine based on effect of ligand on the emission of Ag nanoclusters and aggregation-induced emission enhancement

Abstract For small size metal nanoclusters, it is expected that template ligand will play an essential role in regulating the properties and structure. Using histidine (His) templated Ag nanoclusters and glutathione (GSH) and dihydrolipoic acid (DHLA) protected silver nanoclusters as models, due to the different electron donating abilities of different ligands, two silver nanoclusters with similar sizes have fluorescence emission peaks at different wavelengths. Furthermore, dopamine (DA) is a good electron donor, but is easily oxidized to dopaquinone, which can act as an electron accepter. Therefore, with addition of DA, which is easily oxidized by dissolved oxygen, the fluorescence of His-Ag nanoclusters quenches. Meanwhile, the ligands of GSH-DHLA-Ag nanoclusters contain sulfhydryl group, which has stronger reducing ability and stronger electron donating ability. Therefore, even in the presence of dopaquinone, the electron-donating effect of the ligand of the GSH-DHLA-Ag nanoclusters on the metal cores does not decrease significantly. Moreover, the addition of DA causes a certain degree of aggregation of GSH-DHLA-Ag nanoclusters, and the fluorescence intensity is enhanced due to the aggregation-inducing emission enhancement effect. Based on two types of silver nanoclusters, a ratiometric fluorescent sensor for DA analysis has been established. The linear range is 0-800 nM, and the limit of detection based on 3δ/s is 10 nM.