Ultrasensitive detection of glutathione based on a switch-on fluorescent probe of AIE-type red-emitting copper nanoclusters

Abstract

Glutathione (GSH) plays key roles in biological systems. It is critically valuable to construct highly sensitive and accurate sensors for its quantification in studying the oxidative stress reaction and related diseases. Here, a rapid switch-on fluorescence assay for detecting trace GSH was developed by combining aggregation-induced emission copper nanoclusters (Cu NCs) with a large stokes shift (Δλ = 235 nm) and MnO₂ nanosheets. The red-emitting Cu NCs act as a fluorometric reporter, and the MnO₂ nanosheets serve as both a fluorescence quencher of Cu NCs and a signal recognizer of GSH. The fluorescence of Cu NCs is quenched by MnO₂ nanosheets through the inner filter effect. Upon introduction of GSH, the MnO₂ nanosheets were reduced to Mn²⁺ and the quenched fluorescence of Cu NCs was recovered. On this basis, an ultrasensitive nanosensor was developed for GSH with a detection limit of 1.2 nM, which is at least 5 times lower than that of previous FL sensors based on MnO₂. The fluorescence sensing strategy was successfully applied for GSH detection in human serum samples with good accuracy and high reproducibility. The result was cross-verified by standard o-phthalaldehyde fluorescence assay, suggesting the potential applicability of this system for the analysis of GSH in practical biological samples, disease monitoring and clinical diagnosis.