Signal-On fluorescence sensor for hydrogen sulfide detection in environmental samples based on silver-mediated base pairs

Hydrogen sulfide (H2S) is a dramatic toxic gas molecule; long term exposure to H2S environment poses a serious threat to human health. It is highly imperative to develop sensitive and selective methods for H2S (used to represent the total amount of H2S, HS- and S2-)detection. In this work, a signal-on fluorescence biosensor for H2S detection has been developed based on silver-mediated base pairs (C-Ag+-C). Two separate C-rich single standard DNAs (ssDNAs) has been synthesized, one was labeled with fluorescein (6-carboxyfluorescein, FAM) and the other had been labeled with quencher (black hole quencher, BHQ1). The two ssDNAs are in a flexible single strand owing to the mismatch of the ssDNA and significant fluorescence intensity was observed. In the presence of Ag+, DNA probes could selectivity capture Ag+ to form double standard DNA (dsDNA) via the C-Ag+-C base pairs, which made the quench of FAM by BHQ1 and low fluorescence signal had been detected. With addition of H2S in the system, the dsDNA will be decomposed into ssDNA since Ag+ could be released from C-Ag+-C by the formation of a more stable complex Ag2S, which resulted in the recovery of the fluorescence intensity. The enhanced fluorescence intensity has a linear relationship with H2S concentration in the range from 0.5 to 20 µM with a detection limit (LOD) of 0.16 µM (S/N=3). The proposed system has been applied to detect H2S (used to represent the total amount of H2S, HS- and S2-) in the air near garbage station with satisfied results