Fluorescent Carbon Dots: Synthesis, Characterization And Application

Fluorescent carbon dots (CDs) are a new class of carbon nanomaterials with sizesbelow10nm, which have generated enormous excitement because of their superiority inchemical inertness, water solubility, low toxicity, resistance to photobleaching and ease offunctionalization. It become a rising star in the nanocarbon family. These excellentproperties make CDs have a great potential application in the fields of biomarkers,environmental analysis and optical sensing. Currently, the preparation and the applicationare in the initial stage. However, most of the methods usually involve complex processes,expensive precursors and severe synthetic conditions. Herein, we creat a facile and greenmethod to prepare CDs by hydrothermal treatment of potato and ultrasonic treatment ofnanographite respectively. The CDs of high fluorescence properties are used inbiochemical analysis. The main contents of the paper are summarized below.(1) Water-soluble fluorescent CDs have been synthesized by one step withhydrothermal methods using potato. The effects of the hydrothermal time, temperature,additive amount of potato and pH on the light emissions from CDs were also studied. TheCDs show a fairly uniform diameter of approximate2~3nm spherical particles, whichhave perfect water dispersion. The characteristic absorption peak of CDs emerge at about280nm and emit a visible strong bright blue light fluorescence with a high quantum yield(14%). The mechanism of the fluorescent emission from CDs was proposed. Moreover,some highly photouminescent CDs were also prepared with other vegetables, fruit, petaland other biomass under the same condition. This makes it possible to produce largequantities of water-soluble fluorescent CDs with good biocompatibility.(2) We report a new method to prepare CDs by ultrasonic treatment of nanographites.The flake graphites were groud into the nano-graphite sheets by our self-developed maglevlaboratory grinder. The nano-graphites were oxidation in the strong acid environment andwere cut into CDs by the ultrasonic treatment. The obtained CDs with the size of1~4nmhave strong light absorption in the range of300nm. The CDs contain a large amount ofoxygen functional groups at the surface, the quantum yield is18%.(3) The detection of copper ion (Cu2+) and L-cysteine (L-Cys) is extremely importantbecause an irregular level of Cu2+or L-Cys is an index for many diseases. In this paper, wecreat a method for highly sensitive and selective detection of Cu2+and L-Cys using CDs asfluorescent probe. The charge transfer process make Cu2+quench the fluorescence of CDs. Upon the addition of L-Cys into CDs-Cu2+, the fluorescence can be recovered. The likelymechanism relies upon L-Cys being able to effectively shelter the quenching due to thebinding of Cu2+and its thiol group, which removes Cu2+from the surface of CDs. Thefluorescence intensity CDs with Cu2+concentration and CDs-Cu2+system with L-Cysconcentration of linear relationship between their linear regression equations were:I0/I=1.069+0.243[Q], I2/I1=1.002+0.003[Q]. Detection limits of2.3×10-8M for Cu2+and3.4×10-10M for L-Cys were achieved. This approach is facile, fast, low cost andenvironment friendly, which it is promising for biological applications.