In situ encapsulation of SQDs by zinc ion-induced ZIF-8 growth strategy for fluorescent and colorimetric dual-signal detection of alkaline phosphatase

Controllable encapsulation of sulfur quantum dots (SQDs) into metal-organic frameworks (ZIF-8) by a surface-bound zinc ion-induced growth strategy, and SQDs@ZIF-8 was successfully prepared for alkaline phosphatase (ALP) detection. The new synthesis procedure involves first binding Zn2+ to the surface of SQDs to form SQDs/Zn, and then via zinc ion-induced in situ ZIF-8 growth to obtain SQDs@ZIF-8, which greatly improved the luminous efficiency of SQDs. The specific process of detecting ALP using pH-triggered fluorescence quenching of SQDs@ZIF-8: firstly ALP hydrolyzes 2-phosphate-l-ascorbic acid trisodium salt (AAP) to ascorbic acid (AA), and then the leakage of SQDs in the SQDs@ZIF-8 leads to a decrease in fluorescence intensity based on the destruction of ZIF-8 skeleton by H+ released by AA. A linear relationship was obtained between the fluorescence intensity and the ALP concentration in the range of 0.15-50 U/L, and the detection limit was 0.044 U/L. Moreover, it was found that free SQDs can be complexed with Fe2+ to produce wine red complexes, and the obtained UV absorbance and ALP concentration have a linear relationship in the range of 10-200 U/L. The detection range of ALP is significantly broadened based on the combination of the above two detection methods. Furthermore, SQDs@ZIF-8 exhibited excellent stability in water and was successfully applied to the fluorescence and colorimetric detection of ALP in human serum.