Dual-emissive silicon quantum dots as a ratiometric fluorogenic probe for alkaline phosphatase activity.

Most fluorescent silicon quantum dots (SiQDs) emit at a single wavelength, which limits their use in ratiometric sensing. Here, we describe the hydrothermal synthesis of dual-emissive SiQDs that showed two distinct peaks at ~ 400 nm and ~ 510 nm under 330 nm excitation. The underlying photoluminescence mechanism was elucidated. Leveraging alkaline phosphatase (ALP)-catalyzed hydrolysis of 4-nitrophenylphosphate disodium salt hexahydrate (PNPP) to 4-nitrophenol (PNP), we developed a ratiometric fluorescence assay for ALP activity that exploits the inner-filter effect among SiQDs, PNPP, and PNP. The sensor delivered a linear signal over the range 1-60 U L- 1 with a detection limit of 0.79 U L- 1 and exhibited excellent selectivity against potentially interfering species. Reliable quantification of ALP in animal serum validates the practical utility of the probe. This work expands the toolbox of fluorescent nanomaterials and offers a simple, robust platform for ratiometric biosensing.