A ratiometric fluorescent probe for pH detection based on Ag 2 S quantum dots–carbon dots nanohybrids

In this study, a novel ratiometric fluorescent nanoprobe for pH monitoring has been developed by synthesizing red fluorescent Ag 2 S quantum dots (Ag 2 S QDs) and green fluorescent carbon dots (CDs) nanohybrids (Ag 2 S 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 (I 500 /I 670 ) in the ratiometric Ag 2 S CDs probes can be used for pH sensing. The results revealed that I 500 /I 670 of Ag 2 S CDs probes was linearly related to pH variation between pH 5.4 and 6.8. Meanwhile, the Ag 2 S 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.