Green Synthesis And Analytical Application Of Fluorescent Carbon Quantum Dots

In the past ten or more years,great efforts have been made in developing a wide variety of synthetic methods to produce fluorescent carbon quantum dots(CDs)with excellent performance.Overall,CDs can be synthesized using both top-down and bottom-up strategies.The former technique such as laser ablation,electrochemical etching,and arc discharge refers to the cleaving or breaking down of large-sized carbonaceous materials into small carbon nanoparticles.The latter approach includes hydrothermal or solvothermal treatment,ultrasonic or microwave-assisted synthesis,thermal combustion,etc.,in which the larger and more sophisticated species are formed by pyrolysis or self-assembly of carbonaceous small molecules as precursors.Nowadays,there has been more interest in the development of bottom-up approaches for the preparation of fluorescent CDs due to the precise control of precursor molecules,ease of techniques,low cost,and practicality and convenience of the procedure with generally nontoxic precursors.It is worth noting that under the strong promotion of the concept of green chemistry,using easily available,cheap and environmentally friendly natural resources as green carbon precursors to develop simple,low consumption and mild synthetic methods to prepare fluorescent CDs has become an active research field.Therefore,in this paper,common and pollution-free substances are used as carbon sources to prepare three kinds of fluorescent carbon quantum dots with different functions,and their properties and applications are studied.The details are as follows:(1)Fluorescent carbon quantum dots(Y-CDs)were synthesized via one-step hydrothermal treatment of an easily available instant dry yeast powder as the precursor.Y-CDs exhibit superior optical and biological merits.Significantly,dopamine(DA)can effectively quench the fluorescence of Y-CDs through inner filter effect and static quenching.Therefore,Y-CDs can be used as a green and economical fluorescent probe to directly monitor the content of DA.The sensing platform displayed great sensitivity and specificity toward DA,the limit of detection(LOD)is30 n M and a wide linear range of 0.05-150 ?M.Benefiting from these outstanding features,the developed label free method has been verified in the rapid detection of DA in human serum samples,and the recovery is satisfactory.Furthermore,Y-CDs has shown low toxicity to MCF-7 cells and well demonstrated suitable for living cellular imaging.More interestingly,the fluorescent Y-CDs could be extended as invisible ink validating the important information storage and anti-counterfeiting.All the results facilitate the great potential of the versatile Y-CDs in developing biosensor for clinical diagnose and other biologically related fields.(2)The abnormal levels of Hg(?)and Cysteine(Cys)will cause many diseases,so the detection of Hg(?)and Cys is very important.Based on the previous work,we prepared a kind of fluorescent carbon quantum dots(Y-CDs)with completely different functions by changing the quality of yeast powder and the concentration of Na OH.The Y-CDs not only has high fluorescence quantum yield,but also has excellent optical characteristics.At the same time,based on the phenomena of fluorescence quenching(Off)and fluorescence recovery(On),we successfully constructed an "On-Off-On" sensor.This sensor can detect Hg(?)and Cys sensitively and selectively,the LOD of Hg(?)and Cys are 35 n M and 78.5 n M respectively,and the detection range is 0-100 ?M.The method is not only simple,rapid and environment-friendly,but also has been successfully analyzed in actual water samples with good recovery.Furthermore,based on the low cytotoxicity of this Y-CDs to Hela cells,it's also been used successfully for cell imaging.(3)A kind of fluorescent carbon quantum dots(H-CDs)with specific response to p H value of BR buffer solution were obtained by hydrothermal method with Honeysuckle as carbon source.The H-CDs has good chemical stability,and its fluorescence intensity shows a good linear decreasing relationship in the range of p H6-13.In addition,H-CDs can also be used for rapid detection of food additive sunset yellow(SY).The LOD is as low as 11 n M and the range of linearity is 0-40 ?M.At the same time,we also applied this method to the detection of SY in fruit juice samples,and the recovery is good.Based on this phenomenon,H-CDs as a probe is expected to be applied to the detection of food additive SY in beverage samples.