Rapid and sensitive detection of alkaline phosphatase and glucose oxidase activity through fluorescence and colorimetric dual-mode analysis based on CuO NPs@ZIF-8 mediated enzyme-cascade reactions.

The combined application of nanozymes and natural enzymes has received widespread attention in recent years. In this work, a simple and efficient method was used to synthesize a composite material of CuO nanoparticle-modified zeolitic imidazolate framework-8 (CuO NPs@ZIF-8) with multiple enzyme activities (glucose oxidase-like and hydrolase-like activities) to detect the activity of natural enzymes through fluorescence and colorimetric (UV-vis) dual-mode detection. The hydrolase- and oxidase-like activities of CuO NPs@ZIF-8 show an acceptable affinity with l-ascorbic acid 2-phosphate trisodium (AAP) and -phenylenediamine (OPD). Using the developed sensor, highly sensitive detection of natural enzymes glucose oxidase (GOX) and alkaline phosphatase (ALP) was achieved through both fluorescent and colorimetric analyses with a wide linear range (fluorescence for GOX: 0.86-1.23 × 10 mU mL, UV-vis for GOX: 0.081-1.62 × 10 mU mL; fluorescence for ALP: 0.042-1.20 × 10 mU mL, UV-vis for ALP: 0.0046-1.23 × 10 mU mL) and low LOQs (fluorescence for GOX: 0.86 mU mL, UV-vis for GOX: 0.081 mU mL; fluorescence for ALP: 0.042 mU mL, UV-vis for ALP: 0.0046 mU mL). Compared to the other fluorescent and colorimetric sensors, this sensor has better catalytic activity due to the addition of GOX and ALP, which can amplify the detection signal and improve the sensitivity. This is the first time that composite material CuO NPs@ZIF-8 with "tandem enzyme" activity was synthesized and applied in the detection of enzyme activity. Additionally, the proposed fluorescent and UV-vis platforms exhibit the capability to detect GOX and ALP in serum samples with satisfactory recovery, indicating potential application prospects in biochemical analysis.