Upconversion nanoparticles with bright red luminescence for highly sensitive quantifying alkaline phosphatase activity based on target-triggered fusing reaction

Abstract 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.