On-site visual quantification of alkaline phosphatase activity in cells using a smartphone-based approach

Alkaline phosphatase (ALP) is a critical biomarker associated with various physiological and pathological processes, making its detection essential for disease diagnosis and biomedical research. In this study, we developed a novel, simple, and portable visual quantification method for ALP activity in cells using an efficient Cu_0.9Zn_0.1S nanomaterial with peroxidase-like properties, integrated into a smartphone-based platform for enhanced usability. The Cu_0.9Zn_0.1S nanomaterial catalyzes the breakdown of H₂O₂, generating ·OH radicals that oxidize the colorless substrate TMB into blue oxTMB, which is subsequently reduced back to TMB by ascorbic acid (AA). We employed an indirect colorimetric approach for ALP detection, leveraging ALP's ability to catalyze the dephosphorylation of l-ascorbic acid-2-phosphate (AAP) to produce AA. This method enabled highly sensitive and precise quantification of ALP with a detection limit of 0.47 mU/L and a linear range from 0.001 to 100 U/L. The established smartphone platform not only facilitated real-time data processing but also transformed the detection system into a portable and accessible laboratory. The method was successfully applied to detect ALP in various cancer cell lines, with the highest levels found in HepG2 cells. Moreover, the results were consistent with those obtained using traditional kit-based methods, highlighting the accuracy and reliability of our approach. The system was also applied to evaluate ALP inhibitors, demonstrating its versatility in biomedical applications. This innovative, cost-effective, and highly sensitive colorimetric sensing strategy offers immense potential for clinical diagnostics, cancer research, and inhibitor screening, particularly in on-site, resource-limited, or emergency scenarios.