VS quantum dot label-free fluorescent probe for sensitive and selective detection of ALP.

As an essential enzyme highly associated with various human diseases, alkaline phosphatase (ALP) plays an important role in human tissues. Developing new materials and strategies for monitoring ALP is thus important. We have developed a novel label-free fluorescent sensing system for ALP activity that is based on the "turn-on" fluorescence of VS quantum dots. The fluorescence of VS quantum dots quenched by Fe can be restored by ascorbic acid, which is generated by hydrolysis of L-ascorbic acid 2-phosphate catalyzed by ALP. Rapid, convenient, and sensitive detection of ALP is achieved in the range from 3 to 1000 U/L (R =0.9985), with a detection limit of 0.27 U/L. The proposed sensor exhibits excellent selectivity for ALP compared with other enzymes and proteins, such as glucose oxidase, lysozyme, trypsin, human serum albumin, and bovine serum albumin. The reliability for ALP determination in human serum plasma has been demonstrated with satisfactory recovery, revealing promising application in clinical diagnosis and biomedical research. Graphical abstract Hydrothermally synthesized VS quantum dots serving as a novel turn-on fluorescent probe for detection of alkaline phosphatase (ALP) activity. AA L-ascorbic acid, AAP L-ascorbic acid 2-phosphate, NAC N-acetyl-L-cysteine.