Ratiometric fluorometric determination of sulfide using graphene quantum dots and self-assembled thiolate-capped gold nanoclusters triggered by aluminum.

A ratiometric-based fluorescence emission system was proposed for the determination of sulfide. It consists of blue emissive graphene quantum dots (GQDs) and self-assembled thiolate-protected gold nanoclusters driven by aluminum ion (Al3+@GSH-AuNCs). The two types of fluorophores are combined to form a ratiometric emission probe. The orange emission of Al3+ @GSH-AuNCs at 624 nm was quenched in the presence of sulfide ion owing to the strong affinity between sulfide and Au(I), while the blue GQDs fluorescence at 470 nm remained unaffected. Interestingly, the Al3+@GSH-AuNCs and GQDs were excited under the same excitation wavelength (335 nm). The response ratios (F470/F624) are linearly proportional to the sulfide concentration within the linear range of 0.02-200 µM under the optimal settings, with a limit of detection (S/N = 3) of 0.0064 µM. The proposed emission probe was applied to detect sulfide ions in tap water and wastewater specimens, with recoveries ranging from 95.3% to 103.3% and RSD% ranging from 2.3% to 3.4%, supporting the proposed method's accuracy.