A novel detection system based on the fluorescence quenching of CdS–Ag2S quantum dots (QDs) was designed for the direct measurement of hydrogen peroxide (H2O2). Experimental results showed that an excellent response to the concentrations of H2O2 was found within the range from 1.0 × 10−6 to 1.0 × 10−2 M with a detection limit of 3.0 × 10−7 M. The CdS–Ag2S QDs have been synthesized at room temperature in an aqueous solution using thioglycollic acid as stabilizing agents, which were spectra-tunable and water-soluble. Different influencing factors including pH, variable ratio of [Cd2+]/[S2−], dopant concentration, precursor concentration, and aging time of CdS–Ag2S QDs were studied. It was found that the emission colors of the prepared CdS–Ag2S QDs could be readily tuned from green to red by varying pH. Furthermore, the CdS–Ag2S QDs were characterized by fluorescence and time-resolved emission spectroscopy, TEM, EDX, XRD, XPS, ESR. The long decay times, large surface area, and good chemical stability of the CdS–Ag2S QDs have made this material suitable as a fluorescence probe.
