Near Infrared Emission of Ag2S Quantum Dots and their Fluorescence Quenched by Gold Nanoparticles

The near-infrared emitting Ag2S quantum dots (QDs) coated with L-cysteine were prepared by one-pot aqueous synthesis at room temperature. Several characterization methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), fluorescence spectrophotometer (PL) and ultraviolet -visible spectrophotometer (UV-vis) were used to characterize the structure, morphology and optical properties of the samples. The effects of gold nanoparticles on the fluorescence of Ag2S QDs were systematically investigated, it was found that gold nanoparticles could enhance or quench the fluorescence intensity of Ag2S QDs in some situation. Within a certain range, the fluorescence intensity of Ag2S QDs shows a linear quenching proportional to the colloidal gold concentration. Under the optimized experimental conditions, the linear range was obtained for colloidal gold concentration from 5.93 - 27.09 ×10-6mol/l (r2 = 0.9956). The determined detection limit (LOD) was about 5.08×10-6 mol/l. The quenching mechanism of Ag2S QDs is discussed. Gold nanoparticles also have similar effects on Ag2Te QDs. A new method for the quantitative detection of inorganic nanoparticles was established, and it provides a new way for the bio-analytical applications.