| Fluorescence-based spectroscopy and imaging techniques have been valued as reliable and quantitative tools in biosciences,considering their simplicity,fast response,high sensitivity and selectivity.With the development of nanotechnology,a series of fluorescent nanomaterials with unique optical and electrical properties have been developed,and it has shown a considerable potential of nanomaterial-based fluorescence analysis method in various applications.Among these nanomaterials,carbon dots have attracted tremendous attentions in the fields of construction,biological imaging,optical devices and catalysis,due to their low toxicity,easy to prepare,good photostability and tunable fluorescence emission.Although they exhibit outstanding performance in fluorescence properties,toxicity,and preparation cost.However,there are several disadvantages that limit their further applications.For instance,the quantum yield of most reported carbon dots is relatively low,which limits their practical applications.Some carbon dots have low specific binding capacity and poor selectivity for target detection owning to the lack of functional groups on their surface.Optical methods based on target-induced fluctuation in fluorescence intensity of the carbon dots have limited accuracy as the single emission intensity change might be influenced by many factors.In this thesis,aiming at the improvement of the aforementioned deficiencies of carbon dots,a series of carbon dots with enhanced fluorescence properties were prepared by using hydrothermal method from different raw materials.The detailed description is listed as follows:1.Synthesis of highly fluorescent N doped carbon dots for cellular imagingThe relatively low fluorescence quantum yield of most reported cardon dots has impede their applications in biochemical sensing.Towards this end,we synthesized highly fluorescent N doped carbon dots by using Luminol and Tris as the raw materials based on the fact that doping with heteroatoms can influence the structural properties and the photoluminescence performance of prepared carbon dots.Carbon dots with quantum yield of 14.8%can be obtained under the optimized conditions including reaction time,temperature and the reactant molar ratio.We further characterized their surface chemistry,optical properties and cytotoxicity.It is demonstrated that the N doped carbon dots exhibit low toxicity,good solubility and excellent photo-stability.We successfully applied the as-synthesized carbon dots for intracellular imaging in Hela cells.The results showed carbon dots incubated Hela cells displayed brightly fluorescence,proving the abilities of these carbon dots to penetrate into the cell membrane and use as a novel fluorescent label in bioimaging.In this work,Luminol and Tris were first used as the precursor to prepared highly fluorescent N doped carbon dots and it provides a new idea for the development of carbon dots with high quantum yield.2.Highly Fe3+-selective fluorescent nanoprobe based on ultrabright N/P codoped carbon dots and its application in biological samplesBy employing adenosine 5’-triphosphate(ATP)as the carbon,nitrogen,and phosphorus source,the N/P codoped carbon dots with high quantum yield and surface functionalization could be simply prepared through hydrothermal treatment.The obtained carbon dots exhibited high quantum yields up to 43.2%,as well as excellent photostability,low toxicity,and water solubility.It is demonstrated that there are many carboxyl groups and phosphoric acid groups on the surface.Based on this result,a novel Fe3+ detection method was developed according to the specific binding capacity between Fe3+ and the phosphoric acid groups on the carbon dots.Because of the Fe-O-P bonds formed between Fe3+ and the N/P codoped carbon dots,this nanoprobe showed high selectivity toward Fe3+ against various potential interfering substances in the presence of EDTA.The fluorescence quenching of as-fabricated carbon dots was observed with the increasing Fe3+ concentration and the calibration curve displayed a wide linear region over the range of 1-150 μM with a detection limit of 0.33μM.With the above outstanding properties,these N/P codoped carbon dots were successfully applied for direct detection of Fe3+ in biological samples including human blood serum and living cells.This nanoprobe showed high fluorescence,good accuracy,and excellent selectivity,which presents the potential practical application for diagnosis of Fe3+ related disease.3.Synthesis of dual-emitting Au/C nanoclusters for highly selective and sensitive ratiometric detection of Hg2+ and Ag+Interference factors,such as the concentration of fluorensent probe,the stability of light source,are often unavoidable in the single fluorescence emission intensity change based sensing method.In order to improve the accuracy of carbon dots-based biochemical analysis,the dual-emitting Au/C nanoclusters were prepared by adding of the amino functionalized carbon dots in the preparation of gold clusters.Take advantage of the reduction of carbon dots and the N atoms on the surface,which can increase the number of anchoring sites for the adsorption of Au3+,the dual-emitting Au/C nanoclusters emission at 440 nm and 610 nm under single-wavelength excitation were obtained.It is demonstrated that only the fluorescence intensity at 610 nm was decreased with the increase of Hg2+ concentration.Moreover,with the increase concentration of Ag+,it is showed that only the fluorescence emission peak at 610 nm was shifted to 575 nm and the corresponding fluorescence intensity was increased.Therefore,a new method for detection of Hg2+ and Ag+ with high sensitivity and specificity has been developed.It is observed that the fluorescence intensity ratio(I440/I610)was linear against the concentration of Hg2+ from 0.1 to 150μM with a detection limit of 7.21 nM,and the fluorescence intensity ratio(I440/I575)was linear against the concentration of Ag+ from 5.0-100 μM with a detection limit of 3.77μM.The dual-emitting Au/C nanoclusters were further successfully applied for paper-based Hg2+ sensing,as well as Hg2+ detection in urine.Compared with the detection method based on "on-off" or "on-off-on" mode,this dual-emitting Au/C nanoclusters could achieve high specific detection with multi-target response and ratiometric signal.4.Label-free carbon dots based ratiometric fluorescence pH nanoprobe for intracellular pH sensingThere are some drawbacks in the carbon dots-based ratiometric fluorescent probe which need the cross attachment of dyes or combined with other fluorescent nanomaterials.With this in mind,the carbon dots showing dual emission bands at 475 and 545 nm under single-wavelength excitation were synthesized by simple one-pot hydrothermal treatment of citric acid and basic fuchsin.It is demonstrated that the fluorescence intensities of the as-synthesized carbon dots at the two emissions are pH-sensitive simultaneously.Based on this,a novel ratiometric fluorescence pH nanoprobe was constructed using the label-free carbon dots.The intensity ratio(I475/I545)was linear against pH values from 5.2 to 8.8 in buffer solution.It also displayed that the carbon dots show excellent reversibility and photostability in pH measurements.With this nanoprobe,quantitative fluorescence imaging for the detection of intracellular pH were successfully applied in HeLa cells.In contrast to most of the reported cabon dots-based ratiometric sensors,this ratiometric probe are low in toxicity,easy to synthesize,and free from labels. |
