Highly selective fluorescence sensor for hydrogen sulfide based on the Cu(II)-dependent DNAzyme

Hydrogen sulfide (H2S) is a highly toxic gas, which poses a serious threat to human health and safety. It is necessary to develop some simple and highly selective and sensitive approach for the detection of hydrogen sulfide. In this study, a highly selective and sensitive fluorescence sensor for H2S detection has been developed on the basis of Cu(II)-dependent DNAzyme. The catalytic DNA strand (Cu-enzyme) was labeled with a quencher (black hole quencher, BHQ1) at the 5′-termini and its corresponding DNA substrate strand (Cu-substrate) was labeled with a 6-carboxyfluorescein (FAM fluorophore) at the 3′-end and an additional quencher was attached on the 5′-end. Cu-enzyme and Cu-substrate could hybridize with each other to form a triplex structure firstly and the FAM emission was quenched by the labeled quenchers. The present of Cu(II) could catalyze the oxidative cleavage of the Cu-substrate and hence caused the releasing of the quencher from the FAM fluorophore and the enhanced fluorescence of the system. However, in the presence of H2S, Cu(II) reacted with H2S to form CuS firstly, hindering the cleavage and the fluorescence enhancement. The decrease of fluorescence intensity had a linear relationship with the concentration of H2S in the range between 0.5 and 25 μM with a detection limit of 0.2 μM (S/N = 3). The proposed method innovatively used fluorescent labeling technology and DNAzyme sensing to detect gaseous hydrogen sulfide, and it has been successfully applied to detect the contamination of hydrogen sulfide gas in the refuse collectors with a simple purification procedure.