Synthesis Of Green-Fuorescent Carbon Dots And Their Applications In Cell Labeling And Analytical Chemistry

Carbon dots (CDs), as a new type of fluorescent nano-material, have shown superior properties in both analytical and bio-analytical applications compared with conventional fluorescent materials. For example, the fluorescence is so stable that after being excited for several continuous hours, the fluorescence intensity remains unchanged; the particle size is only several nanometers therefore they have a strong penetration ability to cells; excellent biocompatibility and low toxicity making them suitable for biological, especially in vivo live labeling and imaging. The obvious advantages of CDs have overcome the deficiencies of conventional fluorescent materials to a certain extent and enable them to replace dye or even quantum dots to become the most promising fluorescent marker in the biomedical field. So far. CDs have been applied in cell labeling, in vivo live imaging, glucose and phosphate detection, etc. Therefore, it is important to synthesize the CDs with high fluorescence intensity and stabllity, and use them in biological and analytical applications. In this work, a kind of green-fluorescent CDs were synthesized and applied in cell labeling and detection of Cu2+, the results were satisfied.Firstly, a novel solvothermal approach to synthesize green-fluorescent CDs was developed using L-ascorbic acid as the carbon source, glycol solution as the solvent. The prepared CDs gave a quantum yield of about5.7%for green-color photoluminescence. The effects of the system’s pH value, the kinds of solvent, the reaction temperature and time, the amount of L-ascorbic acid and glycol on the fluorescence intensity were studied. The optical properties and structures of the prepared CDs were characterized using fluorescence spectrum, UV absorption spectrum, transmission electron microscope (TEM), and infrared spectrum. It was observed that there was a good linear relationship between the fluorescence intensity of CDs solution and its pH value in the range of2.55-5.19, according to the regression equation: y=75.63x+37.91, R=0.9990.Secondly, based on CDs’excellent biocompatibility and low toxicity, strong penetration ability into cells, yeast cells were co-incubated with the CDs solution of proper pH value in an air-bath constant temperature oscillator to realize direct inner cell labeling and imaging. The amount of CDs penetrated into yeast cells under different length of time was studied. It was observed that the CDs entered into yeast cells with4h incubation, and the number of the CDs entered into the yeast cells increased with the increase of incubation time.Finally, the CDs were employed in the detection of copper ions. As a result of specific interaction, the fluorescence intensity of CDs was selectively quenched in the presence of Cu2+. Under optimum conditions, a linear calibration curve was obtained in the range of0.075to1.25mmol·L-1with a correlation coefficient of0.9992according to the linear regression equation of y＝-83.33x+424.30. The detection limit of Cu2+was0.057mmol·L (3a), and the relative standard deviation (RSD) for11replicate measurements of0.500mol·L-1Cu2+was0.76%. The recovery of spiked Cu2+in Benxi Mountain Spring and snow water were102%and105%, respectively. It was also observed that aluminum ions showed marked enhancement on the fluorescence of the CDs, enabling their quantum yield to be36.6%, with the red-shift of excitation spectrum and the blue-shift of emission spectrum.