Application of Carbon Quantum Dots in the Field of Nanosensors

Abstract

Compared with traditional semiconductor quantum dots, carbon quantum dots show adjustable excitation wavelength and emission wavelength, good stability, weather resistance and light resistance. Moreover, their photoluminescence properties, good biocompatibility and easy surface modification provide a wide application in life sciences and tracer sensing. Therefore, the study of carbon quantum dots will definitely promote the development of materials science, and it will also gain more attention for the carbon material family. Firstly, an “on–off–on” fluorescent phosphorus/nitrogen co-doped carbon dot (PNCD) probe was explored for the determination of Cr(VI) and dopamine resulting from the inner filter effect (IFE). The blue-emitting carbon dots with high quantum yields of 25.47% as well as a narrow size distribution were synthesized by a rapid, convenient route using H3PO4 and ethylenediamine as the precursors without any surface passivation. A wide linear region in the range of 7–70 mM with a detection limit of 0.71 mM was achieved for Cr(VI). Moreover, the proper reductants can weaken the inner filter effect to recover the PNCD fluorescence by converting Cr(VI) into Cr(III). Therefore, the PNCDs/Cr(VI) hybrid could also be used as an “off–on” fluorescent probe for detecting dopamine (DA) with a detection limit of 0.49 mM. Consequently, the PNCDs could serve as a powerful fluorescent bi-sensor for detection of both Cr(VI) and DA in practical applications. Then, a kind of water-soluble P, N, B-co-doped carbon quantum dots (PNBCDs) synthesized using a convenient hydrothermal method exhibit many excellent features, such as strong fluorescence, excitation independent emission, high mono-dispersity, good stability, and excellent water solubility with a fluorescence quantum yield of 21.95%. The as-prepared PNBCDs possessed remarkable selectivity and sensitivity towards curcumin with the linear range of 0–1.5 mmol L-1 and the detection limit for curcumin was 68 nmol L-1 (3s/k). Additionally, the wonderfully reversible and repeatable sensitivity to external temperature makes it possible that the PNBCDs could be used as a biocompatible fluorescent ink and for thermo-sensitive devices.