Abstract
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.
Highlights
Quantum dots (QDs) have attracted wide attention in various research areas due to their unique properties, such as highly photochemical stability, broad excitation and size-tunable optical spectra, high extinction coefficients, high quantum yields and narrow emission peaks [1]
Ag2S carbon dots (CDs) nanohybrids showing dual-emission peaks at 500 and 670 nm under a singleexcitation wavelength of 450 nm were prepared by using CDs as templates to develop the ratiometric fluorescent probes, in which green emission can be adopted as the reference signal due to their excellent photostability towards pH
The morphology and size of Ag2S QDs and Ag2S CDs were characterized by high-resolution transmission electron microscope (HR-TEM) and dynamic light scattering (DLS)
Summary
Quantum dots (QDs) have attracted wide attention in various research areas due to their unique properties, such as highly photochemical stability, broad excitation and size-tunable optical spectra, high extinction coefficients, high quantum yields and narrow emission peaks [1]. Several QD-based pH sensors using ratiometric fluorescent sensing have been reported, in which organic dyes were chemically conjugated with QDs as internal reference [14,15]. Carbon dots (CDs) are a fascinating nano-fluorescent material with superior properties including stable photostability, simple synthesis and modification, great biodegradability and biocompatibility [16,17,18], which make them perfect candidates as internal reference in comparison with organic dyes for developing ratiometric fluorescent sensor. We have prepared the Ag2S CDs nanohybrids, which combine the fluorescence property of Ag2S QDs and CDs, to develop a novel ratiometric fluorescent sensor for pH sensing These Ag2S CDs nanohybrids possess two emission peaks at 500 and 670 nm under a single excitation of 450 nm. Our probes which sharply respond to small pH changes within a narrow range are desired
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