| Carbon quantum dots (CQDs) as a new type of fluorescent carbon nanomaterials have attracted much attention in various fields such as sensor, biological imaging and optical devices due to their outstanding optical and electrochemical properties, low toxicity and good biological compatibility, resistance to photobleaching and stable fluorescence.Although CQDs show outstanding performance in fluorescence properties, biological compatibility, synthetic cost and other aspects, their low quantum yields compared to inorganic semiconductor quantum dots and organic dyes greatly limits their application in other fields. Recent studies have shown that surface modification and heteroatom doping of carbon quantum dots can significantly enhance the fluorescence efficiency of carbon quantum dots. But the research progress on heteroatom doping is still slow. As a new type of environmentally friendly nanomaterials, carbon quantum dots can be used to construct fluorescence signal output unit of chemo/biosensers sensors and implantable biosensors. However, the research on the developing of a high selective and high sensitivity fluorescence sensing system and biological detection based on biocompatible carbon quantum dots still remains a challenge. So the research of element doping and surface modification of carbon quantum dots to construct chemo/biosensers is of great importantce in theoretical and practical application.In this dissertation, we proposed surface modification and element doping method to prepare carbon quantum dots with high fluorescence efficiency and tunability of fluorescence emission. By taking advantage of the outstanding performance of the doped carbon quantum dots, a sensitive fluorescence sensing platform for hydrogen peroxide, melamine and glucose is developed. Surface functionalization of carbon quantum dots were bonded with DNA to form fluorescent probe, and then the probe with the graphene oxide or carbon nanotubes was used to construct the self-assembly of chemical sensors. Different carbon quantum dots were bonded with different polynucleotide aptamers to preparate different fluorescent probes, and then the probes with the graphene oxide or carbon nanotubes were used to build different self-assembly of biosensors for single detection of DNA, thrombin, Pb2+ and simultaneous detection of a variety of biomarkers. The main contents are as follows:(1) A facile solvothermal route was employed to fabricate boron-doped carbon quantum dots (BCQDs) by using BBr3 and hydroquinone as the precursor. The BCQDs possess visible fluorescence with high quantum yield up to 14.8%. Glucose oxidase can be used in catalytic oxidation of glucose to product glucose acid and H2O2. Because H2O2 has good fluorescence response on BCQDs, thus, BCQDs can be used for the quantitative detection of glucose.(2) We proposed a simple and efficient route to prepare silicon-doped carbon quantum dots (SiCQDs) by using SiCl4 and hydroquinone as the precursor through a facile solvothermal reaction. The fluorescence of the SiCQDs is substantially enhanced and the emission efficiency of the SiCQDs reaches up to 19.2%. The toxicity test and bioimaging experiments showed that SiCQDs have low cellular toxicity and excellent biolabelling ability. The electron transfer between H2O2 and SiCQDs may carry on the quantitative detection of H2O2. Adding melamine can cause the fluorescent restoration because melamine and H2O2 can form stable structure. So the SiCQDs are used as a novel fluorescence sensing platform for the detection of hydrogen peroxide and melamine.(3) Graphene quantum dots (GQDs) with high quantum yield, monochrome fluorescent were prepared. The as-prepared GQDs were chemically bonded with specific oligonucleotide sequence to prepare probe targeting at Pb2+. A high selective and sensitive fluorescent nanosensor based on GQDs and graphene oxide was constructed. Graphene oxide can be used to distinguish the single-stranded DNA and Pb2+, in addition, the electrostatic attraction and π-π accumulation effect between the graphene oxide and graphene quantum dots can be taken advantage of to achieve quantitative analysis of Pb2+ through fluorescence on-off-on process.(4) We proposed surface modification and element doping method to prepare grapheme quantum dots (GQDs) with high fluorescence efficiency and tunability of fluorescence emission. The as-prepared GQDs were chemically bonded with specific oligonucleotide sequence to prepare probe targeting at DNA. Graphene oxide or carbon nanotubes can be used to distinguish the single-stranded DNA and double-stranded DNA, in addition, the electrostatic attraction and π-π accumulation effect between the graphene oxide and graphene quantum dots or carbon nanotubes can be taken advantage of to achieve quantitative analysis of DNA.(5) Two-colored grapheme quantum dots (GQDs) with different emission peaks were chemically bonded with specific oligonucleotide sequence and aptamer to prepare two probes targeting at DNA and thrombin, respectively. Graphene oxide can be used to distinguish the single-stranded DNA, double-stranded DNA, thrombin aptamer and thrombin, in addition, the electrostatic attraction and π-π accumulation effect between the graphene oxide and graphene quantum dots can be taken advantage of to achieve separately and simultaneous quantitative analysis of DNA and thrombin.(6) Two-colored grapheme quantum dots (GQDs) with different emission peaks were chemically bonded with two kinds of specific oligonucleotide sequences to prepare two probes targeting at DNA targets. Carbon nanotubes can be used to distinguish the single-stranded DNA and double-stranded DNA, in addition, the electrostatic attraction and π-π accumulation effect between the carbon nanotubes and graphene quantum dots can be taken advantage of to achieve quantitative analysis of multiple DNA targets through two cycles of fluorescence on-off-on process. |
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