Colorimetric and Fluorescent Determination of Alkaline Phosphatase and Ascorbic Acid based upon the Inner Filter Effect using up-Conversion Nanoparticles

A novel fluorescence and colorimetric dual probe based upon the inner filter effect (IFE) is reported to selectively and sensitively determine alkaline phosphatase (ALP). First, up-conversion nanoparticles (UCNPs) were prepared via a facile hydrothermal method and characterized by transmission electron microscopy (TEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), and zeta potential. Under near infrared (NIR) excitation at 980 nm, the prepared nanoparticles emit green light at 541 nm. The absorption band of p-phenylenediamine (PPD) overlaps the emission of UCNPs, which effectively quenches the fluorescence of UCNPs. However, ascorbic acid (AA) generated from the reaction of ascorbic acid 2-phosphate (AAP) and ALP impedes the oxidation of PPD and the fluorescence is restored. Based on this change, a “turn-on” sensor was used to determine AA and ALP with the limits of detection of 2.49 μM and 0.018 U/L, respectively. The constructed assay was applied to determine ALP in serum and the recoveries were from 93.3% to 101.3% with a relative standard deviation from 1.1% to 3.3%. A facile and efficient approach is reported for the determination ALP and offers a theoretical basis for the related diseases.