The sensitive fluorescence assay of phosphates and alkaline phosphatase based on terbium nanocomplexes synthesized via ligand proportion regulation

Bimetallic dual-ligands terbium nanocomplexes (Tb/DPA/Fe/SSA NCs) with unique internal structure was fabricated by in situ coordination assembly of the Tb3+, Fe3+ and antenna ligands of 2,6-pyridine dicarboxylic acid (DPA) and sulfosalicylic acid (SSA). Interestingly, the regulation of internal ligand SSA proportion endows the nanocomplex with unique structural heterogeneity, which leads to excellent sensing specificity. The formed terbium nanocomplex 1 (NC1) with low SSA ligand (nSSA:nFe3+=1) contributed to the detection of phosphate (PO43-), and its high degree of freedom competes for the internal metal sites of the loose structure NC1, thus recovering the fluorescence of NC1. The enhanced fluorescence intensity of NC1 shows a wide linear relationship with the concentration of PO43- in the range of 1–280 μmol/L and 280–640 μmol/L, and the detection limit is 0.3 μmol/L. Terbium nanocomplex 2 (NC2), where high proportion of SSA ligand (nSSA:nFe3+=6) promotes NC2 to be a coordination saturated nanocomplex, has an extraordinary fluorescence response to pyrophosphate(PPi) instead of PO43-, and PPi with multidentate coordination structure can compete for metal sites in NC2, resulting in enhanced fluorescence. Utilizing the difference of fluorescence response to PPi and PO43-, NC2 serves as a fluorescent probe to detect ALP and exhibits detection limit of 0.26 U/L. As fluorescence probe, Tb/DPA/Fe/SSA NCs have the outstanding merits in simple preparation and rapid response, which has been accomplished for PO43- and ALP analysis in biological fluid samples.