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Luminescent materials with aggregation-induced emission (AIE) have been widely used in chemosensors and biosensors based on signal change induced by physical aggregation of AIEgens. In this work, a novel coordinate bonding-induced emission (BIE) phenomenon of gold-glutathione complex was proposed and identified, and this specific coordinate BIE was further utilized to develop signal-enhanced methods for quantification of aluminum species including aluminum cation and polyoxocation AlO4Al12(OH)24(H2O)127+. Gold-glutathione (Au-GSH) complex has shown significant aggregation-induced emission characteristic, and it can sensitively respond to multiple external stimuli such as solvent polarity and pH via an emission-enhancing fashion. It is found that the introduction of aluminum cation to Au-GSH complex is able to more greatly enhance the luminescence through a coordinate bonding-induced emission process, and this BIE behavior is attributed to strong force induced by coordination reaction between glutathione ligands and aluminum cation. In comparison with AIE process, coordinate BIE process was shown to be a more efficient way to enhance the emission. This BIE property of Au-GSH complex was employed to measure aluminum cation and polyoxocation Al13 with good selectivity. This work provides a new coordinate bonding-induced emission phenomenon, and gives a demonstration of designing chemosensors for metal cations based on coordinate BIE process.

A fluorometric biosensor has been developed to sensitively detect α-glucosidase activity and screen α-glucosidase inhibitors based on carbon quantum dots nanoprobe through supramolecular self-assembly. β-Cyclodextrin was covalently bonded to the surface of carbon quantum dots to prepare β-CD-CQDs nanoprobe. The presence of 4-nitrophenol drives self-assembly between β-CD-CQDs nanoprobe and 4-nitrophenol through host-guest recognition. This supramolecular assembly exhibits non-fluorescent nature, which results in strong quenching of the fluorescence of β-CD-CQDs nanoprobe. When 4-nitrophenyl-α- d -glucopyranoside was chosen as the substrate, it would be readily hydrolyzed to 4-nitrophenol in the presence of α-glucosidase. The linear correlation of quenched fluorescence to α-glucosidase level can be used to establish quantitative detection of α-glucosidase activity. The detection limit of this method can be lowered as 0.6 U/L, and possesses excellent sensitivity and selectivity. The function of this method to screen inhibitor of α-glucosidase was also assessed using acarbose as the example, and positive results supported its feasibility to screen potential inhibitors of α-glucosidase. This work proposes a new signal transduction mechanism through supramolecular assembly, and provides a sensitive detection method for α-glucosidase activity.