Preparation Of Heteroatom-doped Carbon Dots And Their Applications In Chemical Biosensing

Carbon dots?CDs?are a kind of fluorescent nanoparticles with the size of less than 10 nm.Due to their unique fluorescence characteristics,such as favourable biocompatibility and high stability,carbon dots have become favorable materials for biomedical and sensing applications.Because there are abundant carbon sources which are available for selection,the cost of carbon dots is relatively low,and the corresponding preparation processes are relatively simple.It has been applied to functionalize the surface of carbon dots to obtain specific and sensitive responses to analytes for sensing and biomedical research.Currently,the common strategy of surface functionalization of carbon dots includes the incorporation of heteroatoms into carbon dots.The electronic properties of carbon dots are adjusted by heteroatoms doping,accompanying the change in electron transition ability of carbon dots between the lowest unoccupied molecular orbital?LUMO?and the highest occupied molecular orbital?HOMO?.Meanwhile,incorporation of heteroatoms enhance the photoluminescent performance of carbon dots.This thesis combines the advantages of heteroatom-doped carbon dots and optical sensing technology to carry out a series of research work,and the specific contents are as follows:1.A fluorescence"turn-off"biosening method based on nitrogen/phosphorus co-doped carbon dots?N/P-CDs?for iron ions(Fe³⁺)detection.Rich phosphate groups of the surface of N/P-CDs offer possibility for the combination between Fe³⁺and N/P-CDs,resulting the fluorescence signal of N/P-CDs quenched efficiently.Thus we developed a fluorescent"turn-off"biosening strategy for Fe³⁺detection based on N/P-CDs.Given this method,the constructed sensing platform showed the value of economy and environment with a limit detection of 0.10?M and response time of only 30 seconds,possessing the potential in physiological and pathological research.2.A fluorescent"turn-on"biosening method based on silicon and nitrogen co-doped carbon dots?Si,N-CDs?was established for ascorbic acid?AA?detection.This strategy used green-emitting Si,N-CDs as signal indicator and manganese dioxide?MnO₂?nanosheets as quencher.Si,N-CDs can load to the negatively charged MnO₂ nanosheets,resulting the weaken fluorescence signal with the generation of Si,N-CDs@MnO₂ composites.Since the certain overlap between fluorescence emission spectrum of Si,N-CDs and absorption spectrum of MnO₂ nanosheets,it provids a good platform for the occurrence of the fluorescence resonance energy transfer mechanism.When reductive AA is introduced to the above system,MnO₂nanosheets are deconstructed to Mn²⁺ions and the fluorescence of Si,N-CDs is monitored again.A fluorescent"turn-on"biosening strategy was designed for determination of AA with a detection of limit up to 0.102?M based on Si,N-CDs.Additionally,this method successfully applied to achieve the analysis of AA in commercially available vitamin C chewable tablets,displaying a certain application prospect.3.A fluorescent"turn-on"biosening method based on nitrogen-doped carbon dots?N-CDs?was developed for dopamine?DA?detection.As a common chemical reducing agent,the ortho-diphenolic hydroxyl group attached to the surface of DA has a strong electron donating effect,which can change the push-pull electron system of N-CDs,resulting the change in fluorescent properties of N-CDs.Based on N-CDs,a fluorescent"turn-on"biosening strategy was exploited to determine DA sensitively and specially with a detection limit as low as 33.3 nM.DA could also be recognized in human urine and fetal bovine serum,and this method had also been applied to the monitoring of exogenous DA in human neuroblastoma cells.