The Scattering Effect-Based Smartphone-Assisted Colorimetric Sensing for Alkaline Phosphatase Detection

A novel, cost-effective, label-free biosensing strategy has been established for real-time quantification of alkaline phosphatase (ALP) activity, integrating the Tyndall effect with smartphone imaging technology. This method utilizes a handheld laser diode to probe the enzyme-triggered in situ assembly of Cu-guanosine monophosphate (Cu-GMP) coordination polymers, which exhibit tunable Tyndall scattering properties. In the absence of ALP, Cu²⁺ ions chelate with GMP to form Cu-GMP coordination polymers, generating an intense Tyndall effect. Conversely, ALP-mediated hydrolysis of GMP disrupts the formation of Cu-GMP coordination polymers, resulting in diminished light scattering. The intensity of the Tyndall effect is directly proportional to the concentration of Cu-GMP coordination polymers, which in turn correlates with ALP activity levels. A comprehensive investigation of experimental parameters was conducted, including pH, incubation temperature, GMP concentration, incubation time, synthesis duration, and CuSO₄ concentration. Under optimized conditions, the developed smartphone-assisted colorimetric assay enables the detection of ALP activity within the range of 0.375-3.75 U/mL, with a limit of detection of 0.184 U/mL. The application of this method to serum samples yielded recovery rates ranging from 102.6% to 109.0%. In summary, this smartphone-based colorimetric platform offers a portable and versatile approach for instrument-free detection of ALP activity, with potential applications in point-of-care diagnostics and resource-limited settings.