Research On The Synthesis Of Red Carbon Dots And Their Application In Analysis And Detection

As a promising luminescent nanomaterial,carbon dots（CDs）are widely used in biomedical applications due to their unique advantages such as easy preparation,excellent optical properties,good biocompatibility,and tunable modification of structure and function.The great potential of the has received great attention.However,most of the reported CDs have insufficient excitation and emission in the red/near-infrared（R/NIR）region,which greatly limits their practical application in biomedical detection and therapy.Therefore,in recent years,extensive research has been carried out to produce CDs with enhanced R/NIR excitation and emission for sensing by designing reactions and precise separations.Some ions in the environment can enhance human immunity and have the ability to prevent and resist diseases.Some of them can cause human poisoning and cancer.Such as iron,copper ions,nitrite（NO₂^-）.Amino acids are one of the biologically active macromolecules that build biological organisms,which can provide energy for the body and brain activities and play a role in nitrogen balance in the human body.In addition,abnormal amino acids in the human body can cause certain diseases.Abnormalities such as glutathione（GSH）can cause cancer,cystic fibrosis,cardiovascular and other diseases.Alkaline phosphatase（ALP）is a functional protein with specific and efficient catalytic ability for substrates.Abnormal levels of its human body can lead to liver dysfunction,bone disease and other diseases.Therefore,it is necessary to develop convenient and quick methods to detect them by exploiting the properties possessed by CDs.In the introduction,this paper mainly summarizes the advantages of R-CDs and NIR-CDs,analyzes the key influencing factors for the synthesis of CDs with long-wavelength emission characteristics,discusses the possible fluorescence mechanisms,and summarizes their use in imaging,transmission applications in the fields of sensory and cancer therapeutics.Due to the unique characteristics and advantages of R-CDs and NIR-CDs,long-wavelength CDs were prepared by a simple method and a series of different types of detection methods were constructed to detect heavy metal ions in the environment and human amino acids and hydrolases,etc.The work of the four systems,the main research contents of the paper are as follows:（1）R-CDs with high quantum yield（45%）were rapidly synthesized by pyrolysis of2,5-diaminotoluene sulfate and 4-hydroxyethylpiperazineethanesulfonic acid（Hepes）in a microwave reactor.The optimal excitation and emission of this R-CDs are 585 nm and 607 nm,respectively,and the Stokes shift is 22 nm.Since Fe³⁺can quench the fluorescence of R-CDs,R-CDs were developed as highly sensitive fluorescent"on-off-on"sensors for sensing Fe³⁺and L-ascorbic acid（AA）.R-CDs have excellent fluorescence properties.The fluorescence of R-CDs was selectively quenched by Fe³⁺by static quenching,which was successfully used to detect Fe³⁺with a detection limit of 0.28μM.AA was added to repair surface defects,resulting in the fluorescence of R-CDs gradually recovered.By this principle,an"on-off-on"detection strategy for AA was constructed with a detection limit of 0.42μM.In addition,the detection of Fe³⁺in different water samples and AA in human body fluids also showed the prospect of this probe for practical application,which is expected to be an effective and efficient"on-off-on"nanosensor.（2）R-CDs were synthesized by one-step hydrothermal method using N-（4-aminophenyl）acetamide and 2,3-difluorophenylboronic acid as precursors.Furthermore,the optimal excitation and emission of the synthesized R-CDs were 520 nm and 602 nm,respectively,and the Stokes shift was 82 nm.Due to the excellent optical stability of R-CDs,since dopamine（DA）can be formed polydopamine（PDA）with green fluorescence by self-cyclize in an alkaline environment,the red fluorescence of R-CDs can be passed through by the generated PDA.Inhibition of the inner filter effect.Since AA has reducibility,it can prevent the oxidation of DA and thus the fluorescence of R-CDs can be recovered.The addition of ALP can enable AAP to generate AA to establish a sensing platform based on R-CDs/DA to detect ALP.After a series of detection optimizations,by calculating the ratio of the fluorescence signal of R-CDs to PDA,the LOD of ALP can be calculated as 0.044 U/L,and a good result is obtained in the detection of ALP in human serum.（3）R-CDs were synthesized by a solvothermal method using citric acid（CA）and4,5-difluoro1,2-phenylenediamine.The optimal excitation and emission of the synthesized R-CDs were 550 nm and 619 nm,respectively,and the Stokes shift was 69 nm.R-CDs have good optical stability and biocompatibility.Since R-CDs are extremely sensitive to p H and exhibit a superior linear relationship in the range of p H 4-13,which can potentially be applied to the detection of the microenvironment of organisms.In addition,the fluorescence of R-CDs can be selectively quenched by Cu²⁺through a static quenching mechanism,and Cu²⁺has a stronger complexing ability with GSH,which can fall off the surface of R-CDs and combine with GSH,thereby R-The fluorescence of CDs can be recovered.The detection limits of Cu²⁺and GSH were 0.16μM and 0.41μM,respectively.In addition,the detection of Cu²⁺in different water samples and the detection of GSH in human urine and blood samples showed that the probe has certain practical application prospects,and is expected to be an effective and efficient"on-off-on"fluorescent nanosensors.（4）NIR-CDs were synthesized via one-step hydrothermal method using4,5-difluorobenzene-1,2-diamine and N-（4-aminophenyl）acetamide as raw materials.The optimal excitation and emission of the synthesized NIR-CDs are 530 nm and 675 nm,respectively,and the Stokes shift is 145 nm.NIR-CDs can be used as fluorescent probes for nitrite detection by binding to the complex of bathophenanthroline disulfonic acid（BPS）and Fe²⁺ions.The red BPS-Fe²⁺complexes can quench the fluorescence of NIR-CDs through the inner filter effect,while Fe²⁺can be oxidized by nitrite in an acidic environment to form Fe³⁺,the resulting BPS-Fe³⁺complexes are colorless and unstable,and make fluorescence recovery of NIR-CDs.The limit of detection for nitrite detection was 0.056μM.The method shows good applicability by analyzing complex real samples,contaminated soil extracts,and human urine samples.