A reusable copper-cysteamine fluorescence probe for cost-effective detection of alkaline phosphatase activity based on a redox-modulated inner filter effect

The cost-effective and eco-friendly monitoring of alkaline phosphatase (ALP) activity is crucial for the diagnosis and treatment of various diseases. In this study, we investigated the utilization of a two-dimensional (2D) sheet-like copper-cysteamine (Cu-Cy) as a fluorescence probe for the detection of ALP activity. It was found that the fluorescence emission of Cu-Cy could be reversibly switched off and on by the alternate addition of manganese dioxide nanosheets (MnO₂ NSs) and ascorbic acid (AA) based on a redox-modulated inner filter effect. Additionally, owing to its 2D structure and exceptional stability, Cu-Cy exhibited effective reusability for at least four cycles without any noticeable loss in sensing performance. Based on these findings, an efficient fluorescent approach was designed for ALP detection by monitoring the generation of AA through the hydrolysis of L-ascorbic acid 2-phosphate catalyzed by ALP. The assay achieved a detection limit of 0.1 U/L with a linear detection range from 1 to 100 U/L. Furthermore, this sensing method enabled the detection of ALP in human serum and saliva samples, as well as distinguishing between the saliva of healthy individuals and patients with periodontitis. Moreover, this approach demonstrated significant potential for ALP inhibitor screening, thus offering promising prospects for clinical diagnosis and treatment of ALP-related diseases.