Metal-ion-mediated fluorescent carbon dots for indirect detection of sulfide ions

Abstract

Because of the fact that carbon dots (CDs) generally do not show satisfied fluorescence activities, developing indirect approaches to use these nanomaterials as fluorescence probes is of increasing interest. In this study, two novel metal-ion-mediated fluorescent probes based on CDs for the indirect detection of sulfide ions are presented. The first probe was established using CDs in the presence of Hg2+ ions and utilized as a fluorescence-enhancement probe. In this case, Hg2+ efficiently quenched the fluorescence of the CDs and subsequent addition of sulfide ions removed them from the surface of CDs resulting in regenerating the fluorescence. This probe was used for detection of sulfide over a linear concentration range of 2–10μM and a detection limit of 0.32μM. In the second probe, CDs in the presence of Ag+ was utilized as a fluorescence-quenching probe. Here, the fluorescence of CD/Ag+ was significantly quenched by sulfide while, Ag+ itself cause only a slight change in the fluorescence intensity of CDs. The quenching process was found to be based on the inner filter effect (IFE) of the formed Ag2S particles which absorb both the excitation wavelength and emission spectrum of CDs. This probe allowed detection of sulfide over the range of 1–100μM and a detection limit of 0.43μM. We validated the practicality of this probe for determination of sulfide ion concentration in tap and mineral waters with good recoveries.