Ratiometric Fluorescent Detection of Phosphate in Aqueous Solution Based on Near Infrared Fluorescent Silver Nanoclusters/Metal-Organic Shell Composite.

Synthesis of near-infrared (NIR) fluorescent AgNCs with high quantum yield and stability is challenging but important for sensing and bioimaging application. Here, we report the fabrication of AgNCs/metal-organic shell composite via the deposition of metal-organic (zinc-nitrogen) coordination shell around AgNCs for ratiometric detection of phosphate. The composite exhibits NIR emission at 720 nm with 30 nm red-shift in comparison to bare AgNCs and a weak emission at 510 nm from the shell. The absolute quantum yield of NIR fluorescence of the composite is 15%, owing to FRET from the shell to the AgNCs core under the excitation at 430 nm. Besides, the composite is stable due to the protection of the shell. On the basis of the composite, a novel ratiometric fluorescence probe for the detection of phosphate in aqueous solution with good sensitivity and selectivity was developed. The limit of detection (3s) is 0.06 μM, and the relative standard deviation for 10 replicate detections of 10 μM phosphate was 0.6%. The recoveries of spiked phosphate in water, human urine, and serum samples ranged from 94.1% to 103.4%.