Ratiometric Fluorescent Detection of Phosphate in Human Serum with Functionalized Gold Nanoclusters Based on Chelation-Enhanced Fluorescence

We report a new fluorescent nanoprobe simply constructed by the surface modification of positively charged polyethylenimine (PEI)-coated gold nanoclusters (AuNCs) with 8-hydroxyquinoline-5-sulfonate (8Q5S) through electrostatic interaction. This nanoprobe showed the intrinsic emission of AuNCs at 650 nm and a weak emission at 490 nm from 8Q5S. Based on chelation-enhanced fluorescence of 8Q5S induced by its specific and high affinity for phosphate upon binding Mg2+ and the stable fluorescence of AuNCs as the reference, this nanoprobe was demonstrated to exhibit highly sensitive, selective, and reliable detection of phosphate in the linear range from 0 to 50 mu M with a low detection limit of 0.14 mu M. Furthermore, the presented ratiometric fluorescent sensor was successfully employed for accurate quantitation of phosphate in complex human serum samples with satisfactory results.