Inter filter effect between fluorescent copper nanoclusters and Cr(VI) and its application for probing the activity of alkaline phosphatase

Herein, a novel fluorescent sensing strategy for the detection of alkaline phosphatase activity (ALP) was successfully established using highly luminescent glutathione-stabilized copper nanoclusters (GSH-CuNCs) as fluorescent probe. The GSH-CuNCs were synthesized with GSH as stabilizer and ascorbic acid (AA) as reductant. The optical properties of GSH-CuNCs were further investigated using fluorescence and UV–vis spectrophotometry. And its sensing ability for AA and ALP were explored. The fluorescence intensity of GSH-CuNCs was strongly quenched by Cr(VI) due to the inner filter effect (IFE). However, in the presence of AA, the fluorescence of GSH-CuNCs/Cr(VI) probes was restored due to the weakening of the IFE. It also exhibited a good linear range to the concentration of AA in the range of 0.1–500 μM, and the detection limit was 20 nM. In addition, it has been found that the substrate ascorbic acid 2-phosphate (AA2P) had no effect on the fluorescence of the (GSH-CuNCs)-Cr(VI) probe. Since ALP could specifically hydrolyze AA2P into AA, the emission intensity of the probes was restored by an ALP-triggered reaction. As a result, ALP was sensitively and selectively quantified with a wide linear range of 0.1 mU•mL−1 to 200 mU•mL−1 and a low detection limit of 0.02 mU•mL−1. In order to evaluate the practicality of the detection strategy, ALP in real sample analysis was also determined. The results showed that the recoveries and relative standard deviations were acceptable towards the probes. The proposed biosensor could be applied in fields of environmental and biological analysis.