| Emerging as the newcomers to the fluorescent nanomaterials,carbon dots was considered as a potential alternative for quantum dots owing to their outstanding fluorescent properties,low toxicity and favorable biocompatibility.Also,due to the remarkable properties consisting of stable photoluminescence,electro-optic properties and resistance photobleaching,carbon dots has attracted tremendous attentions.Over the past few years,great efforts have been exerted on the vast potential applications and more detailed fundamental studies of CDs in the fields of biological labeling,pharmaceutical analysis and drug delivery.However,investigating simpler,more environmentally friendly and rapid methods for synthesizing CDs with good fluorescent performance and extend its application are still in emergency.In this thesis,a more convenient and rapid preparation method to synthesis carbon dots has been explored.Then,the cytotoxicity and biocompatibility of these CDs were also investigated.Based on the outstanding properties,CDs was subsequently applied for cell imaging,p H sensing and bacteria assay which were closely related to human health.The main research contents are as below:(1)Carbon dots originated from carnation for fluorescent and colorimetric pH sensingAn innovative and green strategy for synthesizing CDs has been built up by using carnation as carbon source for the first time.Briefly,carnation petals were heat on the wire coil heater for 2 min to obtain fluorescent CDs,which showed blue fluorescence together with a quantum yield of 11.36%.Also,the as prepared CDs showed excitation-dependent emission character and high salt tolerance.The high resolution transmission electron microscope(HR-TEM)indicated that these CDs were uniform in size and well-dispersed,and the diameter of CDs existed in the range of 6-10 nm also confirmed by Dynamic light scattering(DLS)histogram.Fourier Transform Infrared Spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and 13 C NMR revealed that the prepared CDs were mainly composed of C and O as well as limited amount of N.Meanwhile,there existing O-H,N-H,C-H,C=N,C=O,C=C and C-O groups on the surface of the current CDs.Significantly,these CDs have a distinct pH-sensitive feature,based on this phenomenon,a new method for pH sensing was established.To be specific,the fluorescence intensity of CDs exhibits a linear fashion over the pH range of 11.7 to 3.2 with the linear correlation coefficient of 0.991.Simultaneously,the color of the solution varied from yellow to yellow-orange,and the corresponding hue(H)parameter decreased linearly with the pH value range from 10.6 to 5.All these phenomena and evidence illustrated that the produced CDs has potential as colorimetric and fluorescent sensors for pH sensing.Additionally,the cytotoxicity investigation showed that the CDs possessed low cytotoxicity and well biocompatibility,making them suitable candidates for cellular imaging.Meanwhile,the result of the intracellular uptake experiment showed CDs could enter and light the cells.Thus,it could be served as a potential substitute for conventional organic dyes which are easy to photobleach or semiconductor quantum dots(QDs)which are seriously pernicious in bioimaging.(2)Employing carbon dots modified with vancomycin for assaying Gram-positive bacteria like Staphylococcus aureusFoods like milk and meat products are easily contaminated by bacteria once treated in unclean environment,especially staphylococcus aureus.Hence,quantification detection of staphylococcus aureus exhibits great significance for human safety.By forming hydrogen bonds,vancomycin could bind to the terminal peptide of D-Ala-D-Ala on the cell wall of the gram-positive bacteria.Thus,it may act as an intermediate for linking fluorescent signaling molecules and bacteria.Inspired by the attractive fluorescent performance of CDs and the interactions bacteria binding with vancomycin,a facile approach for fast and accurate detection of gram-positive bacteria originated from CDs modified with vancomycin has been established.Specifically,the modified CDs aggregated on the surfaces of bacteria owing to the interactions between vancomycin and bacteria,thereby facilitating the decrease of CDs' fluorescence.Firstly,CDs with blue fluorescence was initially synthesized by using citric acid and urea as carbon sources and heated in a domestic 750 W microwave.The maximum excitation and emission spectra were recorded as 320 nm and 435 nm respectively.HR-TEM imaging indicated that the CDs was spherical and well-dispersed with a diameter of 2-3 nm.Moreover,the FTIR data revealed that there was carboxyl groups on the surface of CDs described here.Consequently,vancomycin could be modified on the surfaces of CDs by-COOH and-NH2,while EDC and NHS function as the crosslinking agents.Secondly,the HR-TEM,FTIR and UV-vis data showed that after modification,vancomycin hardly implied any influence on the properties including the morphology and size,the fluorescent performance and the UV-vis absorption of the CDs.In addition,the MS data demonstrated that there might 2 vancomycin molecular modified on the surfaces of CDs.Finally,the prepared carbon dots were applied to detect Staphylococcus aureus accompanied with a linear range of 3.18×105-1.59×108 cfu/m L as well as a detection limit of 9.40×104 cfu/mL.Meanwhile,the current strategy was applied for detection of other bacteria including Bacillus subtilis,Listeria monocytogenes,Salmonella,Pseudomonas aeruginosa and Escherichia coli,and the modified carbon dots showed obvious affinity with gram-positive bacteria owing to the ligand-receptor interactions between vancomycin and the cell walls,suggesting its value for detecting gram-positive bacteria.Additionally,the practicability of this sensing approach was validated by recovery experiments which the Staphylococcus aureus were grew in orange juice.Simultaneously,the traditional plate-counting method for assaying Staphylococcus aureus in orange juice served as the controls.The results suggested the generally satisfactory recovery,confirming its potential to broaden avenues for detection of gram-positive bacteria.In summary,all research results described above were the exploration about the preparation and characterization of CDs and its application in bioimaging and sensing.These researches would be beneficial for us to further understand the character and function of CDs as well as extending its application in the fluorescence sensing and bioimaging fields. |
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