Carbon quantum dots-Ag nanoparticle complex as a highly sensitive “turn-on” fluorescent probe for hydrogen sulfide: A DFT/TD-DFT study of electronic transitions and mechanism of sensing

We present an efficient carbon quantum dots (CQDs)-modified silver nanoparticles (AgNPs) (CQDs-AgNPs) as turn-on fluorescence nanoprobe for monitoring hydrogen sulfide (H2S) in brain microdialysate. The fluorescence of the CQDs-AgNPs probe can be selectively and sensitively turned on by H2S due to the formation of AgS bonds between AgNPs and H2S and breaking of the AgN bond between AgNPs and CQDs. Density functional theory (DFT)/time-dependent density functional theory (TD-DFT) investigation were thoroughly conducted on the electronic structures, absorption and emission spectra of CQDs-AgNPs complex as well as the sensing mechanism for hydrogen sulfide. The CQDs-AgNPs fluorescent probe illustrates a wide linear detection range towards H2S from 1 to 1900 nM with the detection limit of ∼0.4 nM. This improved sensitivity, lower limit, along with the high selectivity and fast response toward H2S, makes this CQDs-AgNPs complex successfully monitor H2S basal level in rats without exogenous stimulation, which was calculated to be 3.08 ± 0.10 μM (n = 3). This novel fluorescence probe provides an assay for direct detection of H2S in the cerebral systems and contributes to understand the physiological function and molecular mechanisms of endogenous H2S.