A ratiometric fluorescent probe for pH detection based on Ag₂S quantum dots-carbon dots nanohybrids

In this study, a novel ratiometric fluorescent nanoprobe for pH monitoring has been developed by synthesizing red fluorescent Ag₂S quantum dots (Ag₂S QDs) and green fluorescent carbon dots (CDs) nanohybrids (Ag₂S CDs) in one pot using CDs as templates. The nanoprobe exhibits dual-emission peaks at 500 and 670 nm under a single-excitation wavelength of 450 nm. The red fluorescence can be selectively quenched by increasing pH, while the green fluorescence is an internal reference. Therefore, the change of the relative fluorescence intensity (I₅₀₀/I₆₇₀) in the ratiometric Ag₂S CDs probes can be used for pH sensing. The results revealed that I₅₀₀/I₆₇₀ of Ag₂S CDs probes was linearly related to pH variation between pH 5.4 and 6.8. Meanwhile, the Ag₂S CDs probes possessed a good reversibility along with pH changing between 5.0 and 7.0 without any interruption from common metal ions, proteins and other interferences.