A coumarin-based fluorescent probe for sequential detection of Cu2+and GSH with its application in visual sensing

Copper ions (Cu2+) assume pivotal roles in a multitude of biological processes, whereas glutathione (GSH) is equally indispensable for a diverse array of cellular functions. The deficiency or excess of either of these substances can inflict detrimental impacts on both the environment and human well-being. Nevertheless, conventional ion detection methodologies are plagued by substantial shortcomings, such as low selectivity, protracted detection durations, and exorbitant costs. As a result, there exists an acute necessity to develop a straightforward, expeditious, precise, and highly biocompatible probe for the detection of these substances. This paper reports the development of a newly synthesized fluorescent probe X4 derived from 3-aminobenzo[b]thiophene, which enables continuous detection of Cu2+ and GSH through a fluorescence "on-off-on" process. X4 exhibits exceptional accuracy and sensitivity for both Cu2+ and GSH, with limit of detection (LOD) values of 2.07 x 10-7 M and 4.30 x 10-7 M, respectively. The probe responds rapidly within 20 s, and the detection phenomena are clearly observable. Furthermore, the response mechanism of X4 to Cu2+ and GSH has been elucidated through a comprehensive analysis employing multiple techniques, including 1H NMR titration experiments and DFT calculations. Due to its low cytotoxicity, X4 has been successfully applied to detect Cu2+ and GSH in living cells. Moreover, the quantitative analysis of Cu2+ in real samples and a series of visual applications (such as test papers, smartphone detection, food and textile samples) have also demonstrated satisfactory results. In conclusion, X4 allows for convenient, rapid, and accurate quantification of the target analytes within real-world settings and diverse samples. The successful application of X4 in living cells indicates its significant promise and potential for applications in clinical and biological research domains.