Preparation Of Fluorescent Carbon Nanodots And Their Applications In Ions Detection And Cellular Imaging

Small carbon nanoparticles are an emerging member of the carbonaceous nanomaterial family and have been subsequently named as“carbon nanodots”.Generally,carbon nanodots are a type of spherical or sphere-like nanoparticles of less than 10 nm in size.Due to their unique properties,carbon nanodots have a great many potential applications in a range of fields from chemical sensing to bioimaging and thus are appealing to a number of researchers in nanoscience and nanotechnology.Carbon nanodots have been reported for chemical sensors and biological imaging reagent.However,there are still some drawbacks,including relatively low fluorescence quantum yield?QY,usually less than 10%?,low selectivity,high detection limits and short fluorescence emission wavelength,further application is restricted.The high fluorescence quantum yield and long wavelength carbon nanodots are expected to be obtained and applied to the ultra-sensitive detection of metal ions.In this dissertation,four different carbon nanodots are synthesized,which not only improved the fluorescence quantum yield or emission wavelength,but also improved the ion detection,which was further applied to cell imaging.The details are as follows:?1?The fluorescence quantum yield of carbon nanodots synthesized by natural materials is generally less than 10%.A simple,green and low-cost way is developed in the synthesis of fluorescent carbon nanodots with well-distributed size,using one-pot hydrothermal treatment of rose-heart radish.The effect of reaction temperature and time on the fluorescence properties of carbon nanodots is analyzed.The as-prepared CDs with high QY are characteried by UV-Vis spectrum,fluorescence spectrum,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?and Fourier infrared spectrum?FTIR?,the results show that the surface of N-CDs has lots of the NH₂,OH and C=O and the graphitic nature.The as-prepared carbon nanodots display strong fluorescence with a quantum yield of 13.6%,which could be quenched by Fe³⁺.This phenomenon is used to develop a fluorescent method for facile detection of Fe³⁺with a linear range from 0.02 to 40?mol·L^-1and a detection limit of 0.13?mol·L^-1,and further extended to measure environmental water samples with satisfactory recovery.Eventually,human uterine cervical squamous cell carcinoma?SiHa?is used as a model,the low toxicity and strongly fluorescent carbon nanodots are applied for cell imaging and the quenched fluorescence by adding Fe³⁺,demonstrating their potential towards diverse applications.?2?The green-fluorescent Carbon nanodots?G-CDs?are synthesized using lonicera maackii fruit as carbon precursor via a simple hydrothermal treatment.The effect of reaction temperature and time on the fluorescence properties of carbon nanodots is analyzed.It is concluded that the synthesized G-CDs have the characteristics of optimal N doping and surface defects at the appropriate reaction temperature and time,so as to obtain high-quality carbon nano-dots with green fluorescence.The characterizations of the G-CDs mainly include NH₂,OH and carbonyl group.The as-prepared G-CDs have good water solubility and fluorescent stability.The fabricated G-CDs show excellent selective and sensitive detection for Fe³⁺,the photoluminescent intensity of the as-prepared G-CDs is found to be quenched by Fe³⁺ion with a linear range of 0.1-10?mol·L^-1 and a detection limit of 0.08?mol·L^-1?S/N=3?,fluorescence lifetime measurement show that this process has a rapid electron transfer,namely the excited states electrons of surface groups in G-CDs can shift to the empty d orbitals of Fe³⁺,which lead to a series of nonradiative electron/hole restructuring,so as to make the synthesized G-CDs fluorescence decrease obviously.And subsequently,above methods further extend to determine Fe³⁺of real water samples,the results are reliable.After successful application in fluorescent pattering,phenomenon is obvious.Finally,due to its low toxicity,G-CDs are not only applied to multicolor cells imaging,but utilized as bioimaging reagents to detect of Fe³⁺in living cells trough fluorescence changed.?3?We use compounds as raw materials,so as to rapid synthesis of high QY carbon nanodots.In this section,using ammonium citrate and triethylenetetramine by the optimized reaction conditions,a simple,low cost and rapid preparative strategy toward water-soluble luminescent carbon nanodots with high quantum yield?29.83%?are prepared by one-step microwave-assisted method.The structure and optical property of as-prepared N-CDs are characterized.The synthesized CDs exhibit high brightness,favorable biocompatibility and excellent optical stability.Compared to other CDs-based nanomaterials,the fabricated N-CDs show outstanding optical property and excellent selective and sensitive detection for Cu²⁺,the photoluminescent intensity of the as-prepared N-CDs is found to be quenched by Cu²⁺ion with a linear range of 0.01-11?mol·L^-1 and a detection limit of 4.5 nmol·L^-1?S/N=3?,and further extended to determine real water sample.The response of N-CDs to Cu²⁺ions is ascribed to cupric amine complex formed between Cu²⁺ions and amine groups on the N-CDs surface,which leads to the fluorescence quenching through inner filter effect.Additionally,the synthesized N-CDs have been applied for drawing fluorescent patterns,which may be used for anti-counterfeit.Finally,the strongly luminescent and low toxicity N-CDs are applied for living cell fluorescent images and the detection of Cu²⁺in SMMC-7721 cells,indicating as-synthesized N-CDs potential towards diverse application as promising candidate.?4?Using a simple and rapid green route of one-pot hydrothermal method,the luminescent nitrogen-doped carbon dots?NCDs?with high fluorescence quantum yield?46.01%?are synthesized from ammonium citrate and betaine hydrochloride.The optimization of reaction condition for NCDs is 200? for 5h.The as-prepared NCDs have PL emission wavelength independent characteristic,outstanding optics stability and can be further used as a novel probe for sensitive detection of H⁺?linear range from 1.98 to 5.02?,which speculated that exist in the process of proton and deprotonation effect.NCDs can be used for detecting Hg²⁺ions with detection limit as low as 1.69 nM?S/N=3?,by comparing fluorescence lifetime of NCDs before and after adding Hg²⁺,the results show that this process is a static quenching,and a lot of hydroxyl and carboxyl groups of NCDs can be combined with Hg²⁺via chelation,thus formed the complex.Finally,the low toxicity and highly photoluminescent NCDs are utilized as bioimaging reagents to detect of H⁺and Hg²⁺in SMMC-7721 cells by a laser scanning confocal microscope.