A new fluorescent biosensor based on inner filter effect and competitive coordination with the europium ion of non-luminescent Eu-MOF nanosheets for the determination of alkaline phosphatase activity in human serum

The abnormal level of alkaline phosphatase (ALP) in human blood stream indicates health problem. A novel fluorescent sensing system based on competitive coordination with europium ions (Eu3+) integrated in a non-luminescent lanthanide-metal organic framework nanosheets (NO2-Eu-MOF NS) was developed for ALP analysis in human serum. The fluorescence signal is turned-on by the antenna ligand (1,4-phenylenediphosphonic acid (PEPP)) that competitively coordinates with Eu3+ ions from the nanosheet to produce emissive species (Eux(PEPP)y(NO2BDC)z) in-situ. 4-Nitrophenyl phosphate (PNPP) is a substrate of ALP and specifically hydrolyzed into 4-nitrophenol. PNPP exhibits a strong absorption in the UV-Vis region (250–400 nm), which covers the excitation wavelength (280 nm) of Eux(PEPP)y(NO2BDC)z. Therefore, the existing of PNPP causes Eux(PEPP)y(NO2BDC)z non-emissive and, after hydrolysis with ALP, Eux(PEPP)y(NO2BDC)z can be excited and give a detectable fluorescence signal. Based on the fluorescence change, quantitative analysis of ALP activity is thus achievable. This biosensing system was demonstrated in the determination of ALP activity with good linear relationship in the range of 5–1000 U L−1. The limit of detection was 1.1 U L−1 (S/N = 3). The result reveals that the biosensor exhibits excellent sensing performance and anti-interference ability. It could be potentially utilized for clinical routine analysis of ALP activity in human serum.