Fluorescent Carbon Dots: Synthesis, Characterization And Application

Quantum dots (QDs) are superior to commonly used fluophores, inorganic/organic dyes. However, the potential toxicity and relative large size of quantum dots may limit its use in some fields. Therefore, the search for benign nanomaterials of similar optical properties continues.Recently, fluorescent carbon dots (C-Dots), a novel kind of carbonous material have been prepared by several chemists. These carbon dots showed high photostability against photobleaching, tunable excitation and emission wavelength, good biocompatibility and low toxicity, relative small size and low molecular weight compared to quantum dots and other fluorescent nanoparticles. The major research works are as follows:(1) Commercial lampblack, a primary material of Chinese ink, was used to prepare fluorescent C-Dots. The bare nanoparticles have a good fluorescence properties and small size. After passivated the bare C-Dots with O,O'-bis(3-aminopropyl) polyethylene glycol 1500 (PEG_1500N, both the fluorescence quantum yield and fluorescence lifetime improved. These two kinds of carbon dots, i.e., bare carbon dots and bisamino-terminated polyethylene glycol (PEG_1500N) passivated carbon dots, are highly water-soluble and stable toward photo-bleaching. They are stable in water for more than half a year without fluorescence decrease.(2) Applying C-Dots as fluorescent probes for Cu²⁺determination. Copper ions can combine with the negatively charged carbon dots through electrostatic interaction, resulting in fluorescence quenching of the carbon dots, and I₀/I value (I and I₀ are the fluorescence intensity of C-Dots in the presence and absence of Cu2+, respectively.) exhibits a linear relationship with the concentration of copper ions.(3) The addition of Cu²⁺can lead to UV absorption of C-Dots reduced significantly, but don't change fluorescence lifetime of C-Dots. The quenching effect decreased gradually with increasing temperature. The quenching rate constant value is much higher than the upper limit of typical dynamic quenching rate constant. All of these have proved that the fluorescence quenching of passivated carbon dots by Cu²⁺is due to the generation of ground state non-luminous compound, which belongs to static quenching.(4) Water-soluble C-Dots with carboxyl on the surface were conjugated to the amino-terminated DNA via the reaction of 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC) and N-hydrocylsulfo-succinimide (Sulfo-NHS). After conjugated with DNA, the absorption spectra of C-Dots changed, but the fluorescence intensity and the fluorescence lifetime had no significant changes.