A ligand-free up-conversion nanoplatform based on enzyme cascade amplification strategy for highly sensitive detection of alkaline phosphatase

An upconversion signal readout platform for the detection of alkaline phosphatase (ALP) was constructed by combining the inner filter effect (IFE) and the cascade signal amplification strategy. First, 3, 3', 5, 5' -tetramethylbenzidine (TMB) is oxidized by Ag+ to the oxidative product (TMBox), which quenches the up-conversion luminescence (UCL) of the ligand-free up-conversion nanoparticles (UCNPs) through the IFE principle. However, when in the presence of ascorbic acid 2-phosphate (AAP) and ALP, AAP is catalytically hydrolyzed by ALP to produce ascorbic acid (AA), which could not only decrease TMBox formation by reducing Ag+, but also reduce the TMBox generated to TMB, thereby resulting in fluorescence recovery of UCNP. Under optimal experimental conditions, ALP was linearly correlated in the range of 0.15 similar to 8 U/L with a LOD of 0.032 U/L (S/N=3). In addition, the developed method was applied to the detection of ALP in actual serum samples, and the detection result was close to that of the traditional pNPP-based standard assay, which showed that the UCNP-TMB nanosystem has great potential to accurately detect ALP in the clinical bioassay.

Automated summary

An upconversion signal readout platform for the detection of ALP was constructed using the IFE and the cascade signal amplification strategy. The method involved the oxidation of TMB by Ag+ to quench the UCL of UCNPs, which was then reversed by the catalytic hydrolysis of AAP by ALP. The developed method showed a linear correlation between ALP concentration and UCL recovery, and was successfully applied to detect ALP in serum samples.