Preparation And Analytical Application Of Three Fluorescent Carbon Dots

Compared with traditional quantum dots,fluorescent carbon dots（CDs）because of their unique optical properties and chemical properties,small size,good water solubility,biocompatibility,low toxicity and easy realization of surface functionalization aroused the interest of general scientists and has a wide application in many field,becoming one of the most popular carbon nanomaterials.In this paper,fluorescent CDs of blue,green and orange were successfully prepared and applied to the detection of pH value in solution,Cr（VI）,BHC and bio-tissue staining.The content is as follows:（1）The blue CDs were quickly synthesized by microwave method,using m-trihydroxybenzene and sulfuric acid as raw materials.The microwave method was simple in operation,short in time,and economical and convenient.The prepared CDs had a maximum excitation wavelength of 365 nm and a maximum emission wavelength of 465 nm.In the range of pH 1.81⁵.72,the fluorescence intensity of the CDs increased remarkably with the enhancement of pH.Which means that there was a good linear relationship between the logarithm of the fluorescence intensity ratio of the CDs(lg(I_F/I_Fo))and the pH value.Based on this relationship,we tested the concentration of acetic acid in the laboratory and the content of acetic acid in the vinegar and got the satisfactory results.Thus,a method was established that can quickly and easily detect the pH of a solution.（2）A green fluorescent CDs was quickly synthesized by microwave method,using ethylenediamine and nitric acid as raw materials,and a method for detecting Cr（VI）and oral cancer was established by using the new CDs.After the prepared CDs were diluted 50 times,the excitation and emission peaks were 351 nm and 433 nm respectively.Studies showed that Cr（VI）can significantly quench the fluorescence of the CDs and within the range of 0.2-200μmol/L,the Cr（VI）concentration had a good linear relationship with the ratio of the fluorescence intensity of the CDs（（I_Fo-I_F）/I_F）,and the detection limit was 1.7×10^-7 mol/L.When the method had been applied to the detection of Cr（VI）in environmental water samples,there were satisfactory results.When CDs was undiluted,its best excitation and emission wavelengths were 420 nm and 500 nm respectively and emitted green fluorescence.The CDs had good dyeing effect on oral tissue sections,and it was similar to a dye method commonly used in medicine,compared to which,the CDs dyeing was more simple and had clearer imaging effect.Normal tissue and pathological tissues can be distinguished by observed under a microscope.Therefore,a method was established for initial detection of oral cancer.（3）The orange fluorescent CDs,rapidly synthesized by microwave method,using ethylenediamine and formic acid as raw materials,were used to establish a method for detecting berberine hydrochloride（BHC）and oral cancer.The CDs can be used to detect BHC after being diluted 50 times.When the concentration of BHC is 0.2-100μmol/L,the ratio of the fluorescence intensity of the CDs(I_F/I_F0)to the concentration of BHC is in a good linear relationship,and the detection limit was 1.3×10^-7 mol/L.Based on this,we established a sensitive and rapid detection of BHC fluorescent probe,which can be used to determine the content of BHC in compound berberine.Undiluted CDs can be used for section dyeing of oral gingival tissues becuase of their high selectivity to the nucleus of tissue cells and good staining effect on oral tissues.When structural distribution of normal tissues and pathological tissues were observed under a fluorescence microscope,oral cancer could be detected initially.