Highly selective and sensitive gold nanoparticle-based colorimetric assay for PO₄^3- in aqueous solution

A rapid, simple and real-time colorimetric assay for detecting phosphate anions (PO₄^3-) in aqueous solution was developed. The method was based on a novel functionalized gold nanoparticles (MPTP-Zn-AuNPs), which was synthesized by the ligand-exchange reaction of 4′-(4- mercaptophenyl)-2,2′:6′,2″-terpyridine zinc(II) complex (MPTP-Zn) with citrate-stabilized aqueous AuNPs. The strong coordination between MPTP-Zn-AuNPs and PO₄^3- anion gave rise to a color change from wine-red to blue-gray that was discernible by the naked eye and an easily measurable alteration in the absorption spectrum of the particles in aqueous solution. And the new technique exhibited the high selectivity for PO ₄^3- over 11 other anions and could be used to determine PO₄^3- with a detection limit of 11 ppm.