Upconversion nanoparticles with bright red luminescence for highly sensitive quantifying alkaline phosphatase...

Herein, we report a novel ultrasensitive upconversion intense red fluorescence and colorimetric dual-readout strategy for the determination of alkaline phosphatase (ALP) that initially integrates enzyme-triggered cascade signals amplification (ECSAm) with rapid fusing reaction of label-free silver triangular nanoplates (AgTNPs). The sensing strategy involves four aspects. Firstly, AgTNPs with an absorption band at ∼610 nm was synthesized, which can effectively quench upconversion nanoparticles (UCNPs) fluorescence at 670 nm through the fluorescence resonance energy transfer (FRET). Secondly, when in the presence of ALP, l-ascorbic acid 2-phosphate (AAP) was transformed into ascorbic acid (AA) which can react with KIO₃ to produce I₂. Thirdly, the procreant I₂ can quickly adsorb onto the surface of AgTNPs, then etch AgTNPs and the I₂ is reduced to I^-. Fourthly, the generated I^- can further accelerate the fusion of AgTNPs by adsorption effect, which helps achieve ECSAm, allowing the quantitative evaluation of ALP with a satisfying detection limit of 0.035 mU/mL. In addition, the developed method has been further applied to the detection of ALP in human serum with satisfactory results. These results indicate that the dual-readout assay with a well-defined response mechanism shows good prospects in physiological and pathological studies.