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

Abstract 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 Ag S bonds between AgNPs and H2S and breaking of the Ag N 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.