Preparation Of Nitrogen Doped Carbon Dots And Its Application In Detection Of Acidic Small Molecules

Folic acid(FA,also known as pteroylglutamic acid)and caffeic acid(CA,also known as 3,4-dihydroxycinnamic acid)are natural active molecular substances widely found in nature,both of which play an important role in human health,such as Involved in the treatment of leukopenia.At the same time,excessive FA and CA in the human body can lead to abnormal homeostasis of the body system,and even induce a variety of cancers.Therefore,it is very important to realize the quantitative detection of FA and CA.In recent years,fluorescence detection methods had attracted widespread attention in the scientific research due to their advantages of simple preparation and rapid response.And a large number of fluorescent sensing materials had been designed,including organic dyes,quantum dots(QDs),and metal-organic frameworks.These materials had been successfully used for the detection of FA and CA,but the disadvantages of poor fluorescence stability,high toxicity,and poor detection effect limited their further applications.As a newly emerging class of fluorescent nanoparticles,carbon dots(CDs)have greatly promoted their applications in analytical science due to their good water solubility,photostability,and luminescence properties.Based on this,the main research work of this paper is as follows:Nitrogen-doped CDs(N-CDs)were prepared by a one-step hydrothermal method using urea and salicylic acid as raw materials.The obtained N-CDs had excellent properties of strong fluorescence,stable properties,low cytotoxicity and high biocompatibility.Under the excitation wavelength of 295 nm,the maximum emission peak of N-CDs appeared at 410 nm,and its fluorescence quantum yield was 26.5%.Furthermore,the CDs could be used for ultrasensitive detection of FA with an LOD as low as 28 n M.Even the interference of other high-concentration substances did not cause the fluorescence intensity of N-CDs to change,indicating that N-CDs were highly selective in FA detection.Moreover,the quantitative detection ability of N-CDs for FA was analyzed in complex biological environments(urine and FBS samples),with recoveries ranging from 99.50% to104.34%.In addition,the results of cell imaging experiments showed that the CDs had great application prospects in the field of cell imaging.Bright yellow nitrogen-doped CDs(Y-CDs)were prepared by a hydrothermal method using urea and 2,5-dihydroxyterephthalic acid as precursors.The obtained Y-CDs had good dispersibility and excellent photostability.Y-CDs had typical excitation/emission peaks at350/530 nm and exhibited excitation-independent luminescence properties.In addition,after optimizing the experimental conditions,Y-CDs exhibited highly sensitive and selective sensing ability for CA,with a linear range of 0-200 ?M and a detection limit of32 n M.Not only that,Y-CDs were also successfully applied to the sensing of CA in real samples(tea and beverages)with recoveries ranging from 97.32% to 101.84%.At the same time,Y-CDs also exhibited good luminescence properties in anti-counterfeiting imaging,indicating that this CDs had great practical application value in the field of anti-counterfeiting.