The Preparation Of Fluorescent Carbon Dots And Their Applications In The Detection Of Folic Acid And Ciprofloxacin

Carbon dots(C Ds),as a new member of the family of carbon nanomaterials,are attracting more and more attention because of their unique properties and potential applications.Compared with the traditional organic dyes and semiconductor quantum dots,carbon dots not only inherit the advantages of low cost and widely available raw materials,but also have the advantages of simple preparation,easy modification,emission wavelength tunability,good light stability,low toxicit y and biological compatibility.In addition,it also has a special nature in photoelectrocatalysis.Therefore,carbon dots show a broad application prospects in the analysis and detection,catalysis,optoelectronic devices,biosensing and biomedicine and other fields.The preparation method of carbon dots can be divided into: top-down and bottom-up ways.Top-down method mainly includes: ultrasonic method,laser ablation method,electrochemical method and so on.Bottom-up method mainly include: template method,nitric acid reflux method,microwave method,hydrothermal method and so on.In this paper,with regard to the preparation of fluorescent carbon dots and its application,we look for green and environmentally friendly substances as synthetic raw materia ls,explore the simple and rapid synthesis method of fluorescent carbon dots,and study its applications of the detection in folic acid and ciprofloxacin.Specific include the following two aspects:(1)With lactose as the carbon source,carbon dots with light blue fluorescence were synthesized by hydrothermal method under alkaline solution(NaOH).Subsequently,the following characterizations were performed.Observed by high-resolution transmission electron microscopy(HR-TEM),it was found that the dispersion of the carbon dots was good,and the average particle size was about 2-3 nm.The characterized results of infrared spectroscopy indicated tha t the carbon dots have-CH2,-CH3,-OH and-COOH functional groups.Since the carbon dots were specifically bound to folic acid,the carbon dots were employed as selective fluorescence probes for the detection of folic acid.The mechanism may be: The interaction between the water-soluble groups(-OH and-COOH)of carbon dots and the hydrophilic functional groups(-OH,-COOH and-NH2)of folic acid,can form hydrogen bonds,to promote the accumulation of carbon dots,resulting in fluorescence quenching.The decrease of fluorescence intensity was linearly correlated with the concentration of folic acid in a linear range of 6×10-5–8×10-8 mol/L with a detection limit of 1.2×10-9 mol/L at a signal-to-noise ratio of 3.In addition,the system were used for the detection of folic acid in human urine samples,and the recovery rates were between 96.7%-103.0%,suggesting that the fluorescence analysis method established can be successfully used for detecting the samples of folic acid.Folic acid,also known as vitamin B9,a water-soluble vitamins,play an important role in the metabolism in the body.Some diseases are closely related to the deficiency of folic acid,such as megaloblastic anemia,stroke,heart attack,psychosis,infant malformations,cancer and so on.Therefore,it is of great significance to explore the method of the rapid and convenient detection of folic acid.(2)we applied hydroxypropyl methyl cellulose(HPMC),the carbon source,to prepare the blue-emitting carbon dots by hydrothermal method under alkaline solution(NaOH).The as-synthesized carbon dots had been systematically characterized by fluorescence spectroscopy,high resolution transmission electron microscopy,ultraviolet-visible absorption spectroscopy,infrared spectroscopy and X-ray photoelectron spectroscopy.The particle size of the carbon dots was about 5.6nm,and the fluorescence quantum yield was 1.36%.The maximum emission wavelength and the maximum emission wavelength of the carbon dots are at 310 nm and 420 nm,respectively,and the carbon dots showed excitation-dependent emission property.Through the structural characterization,it is proved that the surface of the prepared carbon dots were rich in water-soluble functional groups,such as-OH and-COOH.A new method for the determination of ciprofloxacin had been established,depending on the combination of ciprofloxacin and the surface groups of carbon dots.The linear range is between 90 ?M and 10 nM,with a detection limit of 5.88 nM at a signal-to-noise ratio of 3,which indicates that the detection range is wide and the sensitivity is high.In a word,the fluorescence analysis method can be successfully used for the detection of ciprofloxacin.C iprofloxacin,the third generation of quinolone broad-spectrum antimicrobials,have a good effect on gram-positive bacteria and gram-negative bacteria,which lead to an increase in organism residues.Therefore,the detection of its trace residues is a very meaningful job.