The Synthesis, Characterization, Functionalization Of Carbon Dots And Its Application In Fluorescence Immunoassay

Carbon dots (CDs) are a new class of carbon nanomaterials with strong fluorescenceproperty. CDs possess many oxygen-containing groups at their surface, thus imparting themwith excellent water solubility and suitability for subsequent functionalization with variousorganic, polymeric, inorganic, or biological species. It is expected to be a better fluorescentprobe in the biological sensing fields. This thesis firstly described the synthesis,characterization and functionalization of CDs, and then the interaction of CDs with Hb, BSAand IgG were explored. Furthermore, CDs were applied to detect the IgG in human serum as afluorescent label. It mainly includes the following aspects:1. The synthesis and characterization of CDs16kinds of CDs with excellent luminescent properties were synthesized usingcarbohydrate and fruit peels as carbon sources by ultrasonic, microwave, and hydrothermalmethods. It was demonstrated by X-ray diffraction (XRD) and transmission electronmicroscopy (TEM) that the synthesized CDs were monodispersed and quasispherical withsizes below10nm. Various spectra were measured, and the results displayed that CDsexhibited good water solubility, high resistance to photobleaching and salt, easyfunctionalization, and excellent luminescence properties. Therefore, the as-prepared CDs havegreat potential to be the candidate materials in the fields of fluorescence immunoassay,biosensors and bioimaging.2. Investigating the interaction of CDs and three kinds of proteinsWe studied the influence factors such as the media, concentration of CD1, pH, and so on.The interaction of representative CD1and three kinds of proteins were investigated by usingfluorescence spectrum and synchronous fluorescence spectrum. The results showed that thefluorescence intensities of CD1were quenched with increasing concentrations of Hb, andenhanced with increasing concentrations of BSA and IgG. Moreover, the fluorescenceintensities of proteins were quenched in the presence of different concentrations of CD1. Theabove phenomena confirm the interaction between CDs and different proteins, which lays thefoundation for the immunoassay using CDs as a fluorescence label.3. CDs with high quantum yield as fluorescent labels for human IgG detectionFirstly, according to the reported synthesis methods, CD16with a quantum yield as highas ca.74.6%were synthesized and then carboxylated by bath sonication with NaOH and ClCH2COONa. Subsequently, carboxyl-functionalized CD16were conjugated with goatantihuman IgG (gIgG, antibody) using an EDC/NHS amidization method to obtain theCD16-labeled gIgG, and this obtained conjugate CD16-gIgG was then incubated with a limitedamount of human IgG for immunoreaction between antigen and antibody. Theimmunocomplex formed on the surface of carboxylated CD16resulted in the increase offluorescence intensity. Under the optimal conditions, a linear relationship between the relativefluorescence intensity (F-F0)/F0and human IgG concentration in a range from0.05to2.0μg/mL was obtained with a detection limit of0.01μg/mL. This method has beensuccessfully applied to the determination of IgG in human serum (recoveries equal to95.8%-111.5%). The results indicate the great promise for CDs as labels in fluorescenceimmunoassays.