Silver nanoparticles capped with 8-hydroxyquinoline-5-sulfonate for the determination of trace aluminum in water samples and for intracellular fluorescence imaging

We report on a simple method for the determination of traces of aluminum(III) in water at pH 7.4 by using silver nanoparticles (Ag-NPs) functionalized with 8-hydroxyquinoline-5-sulfonate. The modified Ag-NPs undergo (a) a distinct color change from yellow to deep orange, and (b) a strong fluorescence enhancement upon addition of Al(III). Both the ratio of absorbances at 530 and 392 nm, and the intensity of fluorescence at 492 nm can serve as the analytical information. The absorption-based calibration plot increases linearly in the 0.1 to 4.0 μM Al(III) concentration range. The detection limit is 2.0 nM which is much lower than the permissible level (7.4 μM) for drinking water as defined by the World Health Organization. The method was successfully applied to the determination of Al(III) in samples of lake water, tap water and boiler water, and the recoveries were from 98 to 105 %. The assay also was applied to the determination of Al(III) in living mouse myeloma cells via fluorescence imaging. A linear relationship was obtained between relative fluorescence intensity (F/F₀) and the concentration of Al(III) in the 0.05 μM to 4 μM concentration range. The detection limit is 15 nM.