Preparation Of Carbon Quntumn Dots And Magnetic Nanoparticles And Their Application In Biosensors

The combination of nanotechnology with life science technology has become one of the most important research frontiers. The application of nanomaterials in bioelectrochemistry greatly facilitated the development of bioelectroanalytical chemistry.Nanomaterials have the properties including large surface area, high activity and extremely small size, which fully meet biosensors' requirements of multi-functionalization, miniaturization and high speed. As materials of sensors, nanomaterials have many other advantages such as high sensitivity, fast response and good selectivity. They can be used as fixed materials or carriers, improving the detecting performance of biosensors and significantly increasing the repeatability. Their unique physical and chemical properties have greatly improved the sensitivity of biosensors for detecting biological molecules and cells. The detection time reduced and real-time detection of high flux came true. The discovery and application of many nanomaterials bring a strong vitality to biosensors, which will be widely used in life science.Magnetic nanoparticles are novel nanomaterials with good biocompatibility and active functional groups, which can be combined with DNA, enzymes or antibodies. They are applied into nucleic acid analysis, enzyme immobilization and drug targeting. Because of small size, superparamagnetism, large surface area and good biocompatibility, magnetic nanoparticles can be applied in biosensors. They can significantly improve the sensitivity of biosensors.The discovery and application of carbon nanomaterials have greatly contributed to biosensors. Graphene has a special layer structure and large surface area, which can be prepared for high sensitive sensors. Electrochemical biosensor technology can detect DNA sequences or mutated genes, with good selectivity, high sensitivity and accuracy. Its unique electronic structure provides electron transfer with two-dimensional environment, where electron transfer can be fast and heterogeneous in the margin. Therefore, it is a good electrochemical biosensor material. The advantages of graphene in biosensors are different from other materials. For examples, it can detect small molecules and bacteria, which is very useful in the environment and food safety testing.Carbon dots are a new type of carbon nanomaterials, which have stable luminescent property and a long fluorescence lifetime. As biological markers, its performance is similar to high-performance semiconductor quantum dots for detecting organisms for a long time. Carbon quantum dots with a wide range of excitation wavelength are conducive to simultaneous detection of multiple samples as biological markers. Most important of all, it is safer than previous fluorescent materials and hardly influences molecular biological activity. As biological markers, it is expected to solve the problem of biosafety.This paper will study a safe, fast and simple way to prepare carbon quantum dots. The carbon dots have strong fluorescence signals, high stability and good water-solubility. An innovation is the introduction of magnetic nanoparticles and its combination with fluorescent carbon dots to detect target DNA. Carbon quantum dots are used as fluorescent markers for qualitative and quantitative determination of DNA, which lays a foundation of its further application in biosensors.The main content is as follows:Chapter One IntroductionFirst of all, this chapter introduced the development of nanotechnology, its structural characteristics and application in many respects. Then the advantages, preparation and uses of magnetic materials and graphene were described. Finally, the highlight was a new type of carbon nanomaterials named carbon quantum dots. It has unique structure and nature, whose potential application in biosensors is attractive. The current research status home and abroad is also presented.Chapter Two Ultrasonic-assisted Synthesis of Fe Nanoparticles in the Presence of Poly(N-vinyl-2-pyrrolidone)Zero-valent iron particles were prepared by wet reduction chemistry assisted with ultrasonic treatment. Such prepared particles have uniform sizes, exhibit a crystalline structure and show strong paramagnetic property. Surface modification for these nanoparticles by coating poly(N-vinyl-2-pyrrolidone) (PVP) was investigated. The synthesis conditions to control the nanoparticle size and distribution were exploited. Ultrasonic treatment was an easy and efficient way to control the particles at nano-sizes. PVP modification was employed to make the particles mono-dispersed owing to polymer steric repulsion force. The particles with PVP modification maintain special magnetic properties and high magnetization saturation. Additionally, their size and dispersion are found to be controllable by varying the concentration of PVP and redox agents or by changing the solution adding rate. These particles are expected to be the interesting magnetic materials for various employments, such as biological applications.Chapter ThreeCarbon quantum dots with fluorescence were prepared by electrochemical oxidation of glassy carbon electrode. The carbon dots have good water-solubility and dispersion. After the treatment of nitric acid, its surface carboxylation occurred. It was connected to probe DNA through condensation reaction, which formed fluorescent probe to detect target DNA. Magnetic nanoparticles with a good response to magnetic field were used to purify and separate the biological fluorescent probe. A DNA biosensor of a sandwich structure was constructed based on carbon dots, that is, DNA probeâ… labeled by carbon quantum dots as a fluorescent signal probe, and DNA probeâ…¡labeled by magnetic particles as the capture probe of target DNA. Fluorescence spectrophotometer (FL), high-power transmission electron microscopy (HTEM) and Fourier transform infrared spectroscopy (FTIR) methods were employed to characterize the products obtained, indicating that the carbon quantum dots is a new type of biological fluorescent material. The biosensor has a low detection limit, high sensitivity, high selectivity and biological safety.