A dual-mode sensing system based on carbon dots and MnO2 nanosheets with peroxidase-like activity for the detection of alkaline phosphatase and its inhibitors

Abstract

Alkaline phosphatase (ALP) is widely recognized as an important biomarker for clinical diagnosis. Herein, an innovative fluorometric and colorimetric dual-mode sensing method using MnO₂ nanosheets and carbon dots (CDs) was developed to determine ALP activity. In the presence of H₂O₂, MnO₂ nanosheets exhibited remarkable catalytic activity towards the oxidation reaction of catechol to produce o-benzoquinone. The generated o-benzoquinone effectively quenched the fluorescence of CDs through mechanisms of fluorescence resonance energy transfer and photo-induced electron transfer. ALP can catalyze the hydrolysis of L-ascorbic acid-2-phosphate to generate ascorbic acid, and the generated ascorbic acid can reduce MnO₂ nanosheets to Mn²⁺, thereby inhibiting the oxidation of catechol to o-benzoquinone. This leads to both fluorescence recovery of CDs and a decrease in UV absorption. Using the developed fluorometric and colorimetric dual-mode sensing approaches, ALP activity was determined within the range of 0.5–100 U/L and 4–60 U/L, respectively, with corresponding detection limits of 0.13 and 1.18 U/L. Moreover, the proposed sensing approach was successfully applied to detect ALP in human serum samples and screen potential ALP inhibitors, demonstrating its applicability for medical diagnosis and pharmaceutical development applications.