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.

Automated summary

Sulfur quantum dots (SQDs) were successfully encapsulated into metal-organic frameworks (ZIF-8) using a surface bound zinc ion-induced growth strategy, resulting in SQDs@ZIF-8 for alkaline phosphatase (ALP) detection. This new synthesis procedure significantly improved the luminous efficiency of SQDs. The detection of ALP was achieved by pH-triggered fluorescence quenching of SQDs@ZIF-8, and an extended detection range was obtained by complexing free SQDs with Fe2+. SQDs@ZIF-8 exhibited excellent stability in water and showed potential for fluorescence and colorimetric detection of ALP in human serum.