A signal-on fluorescence sensor for hydrogen sulphide detection in environmental samples based on silver-mediated base pairs

Abstract

Hydrogen sulfide (H₂S) is a dramatically 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 detection. In this study, a signal-on fluorescence biosensor for the H₂S (used to represent the total amount of H₂S, HS⁻ and S²⁻) detection was developed based on silver-mediated base pairs (C–Ag⁺–C). Two separate C-rich single-stranded DNAs (ssDNAs) were synthesized, namely, one was labeled with fluorescein (6-carboxyfluorescein, FAM) and the other was labeled with quencher (black hole quencher, BHQ1). The two ssDNAs were in a flexible single strand owing to the mismatch of the ssDNA, and hence, significant fluorescence intensity was observed. In the presence of Ag⁺, DNA probes could selectively capture Ag⁺ to form double stranded DNA (dsDNA) via the C–Ag⁺–C base pairs, which made the quench of FAM by BHQ1 and low fluorescence signal was detected. With the addition of H₂S to the system, the dsDNA was 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 had 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 was applied to detect H₂S (used to represent the total amount of H₂S, HS⁻ and S²⁻) in air near a garbage station with satisfying results.