Nitrogen and sulfur co-doped carbon dots (N, S/C-dots) were prepared via one-pot hydrothermal treatment of citric acid and cystamine dihydrochloride. The as-prepared N, S/C-dots exhibited excellent excitation-wavelength-independent photoluminescence property and higher fluorescence quantum yield (QY) of 39.7% compared to C,N-dots (QY = 2.6%) prepared using citric acid and 1,6-diaminohexane dihydrochloride as the precursor. The N, S/C-dots were well-dispersed in aqueous solution and showed good photoluminescence stabilities in different pH and temperature without any surface modification. Additionally, the fluorescence of N, S/C-dots can be quenched based on inner filter effect (IFE) upon the addition of Cr(VI) and showed good selectivity and sensitivity to Cr(VI). The detection for Cr(VI) exhibited a good linear correlation ranging from 1 to 80 mu M with a detection limit of 0.86 mu M. What's more, in comparison with other quantum dots and organic dyes, these N, S/C-dots were much more eco-friendly and can be used for multicolor bioimaging. (C) 2016 Elsevier Inc. All rights reserved.