Construction of bifunctional carbon dots based fluorescent/colorimetric/smartphone-assisted multi-signal strategy for monitoring alkaline phosphatase activity

In view of the importance of alkaline phosphatase (ALP) as a clinical diagnostic indicator of related diseases and physiological research, developing a reliable measurement assay with high efficiency and accuracy is of tremendous value. In this study, bifunctional carbon dots (CDs) with peroxidase-like and fluorescence properties were synthesized through a readily available solvothermal method. Peroxidase-like CDs could oxidaze colorless 1,4-phenylenediamine (PPD) to the colored oxidized product (oxPPD), which quenched the CDs' fluorescence. A multi-signal sensing system was strategically fabricated for detecting ALP for the first time, taking advantage of CDs' remarkable peroxidase-mimic activity and fluorescence properties. The limits of detection (LOD) and linear ranges for ALP was 0.034 and 0.027 U/L, 0.1 to 1.8 and 0.05 to 1.8 U/L by the colorimetric and fluorescent method, respectively. Besides, the results of hydrogel devices processed by smartphones also exhibited satisfactory results. The multi-signal strategy developed in this study provides a new impetus for designing different biosensors with bifunctional nanomaterials.