Fluorescent nano-diamond(FND) is an unique fluorescence bio-labeling materials, which exhibit good fluorescence yield, excellent photostability, and non-toxicity. The emission color of FND is determined by the defect centers in the diamond crystal. When the defect center composed of one vacancy and two nearest-neighborhood nitrogen substitutes, it forms a H3 center. H3 center has a zero-phonon line at 496nm , and a broadband green emission around 530 nm,. When the FND contains lots of H3 centers, the emission color is green, hence it¡¦s called green FND(gFND). Since H3 centers composed of two nitrogen substitutes, it is naturally to fabricate the gFNDs by diamonds with high nitrogen substitutes. However, H3 center is not the only products when the diamond contains many nitrogen substitutes, and high density of vacancies. Other type of defect centers (NV-, NV0, ¡K) exhibit lower energy gap, and quench the emission of H3 centers. In this thesis, it aims to study the spectroscopic homogeneity of the gFNDs. Comparing the intensity of the scattering images and the corresponding fluorescence images, it provides the information of the relation between particle size and the density of color centers. Furthermore, images with different color filters are compared to provide the information of the composition of defect structures. Fluorescence lifetime image is performed for the emission dynamics of the nano-particle. The results indicate that the decay lifetime has an relation to the emission intensity. When the nano-particle contains more color centers, it quenches the emission from H3 centers more.

In recent years, tissue engineering has shown great potential in treatment of injured tissues which aims to create artificial structures for cells to regenerate new tissues for replacing the damaged and diseased ones. The selection of scaffold materials is one of the critical factors affecting tissue healing process. Among a wide range of scaffold materials, chitosan (CS) has been demonstrated as an ideal material due to its biocompatibility, nontoxicity, biodegradability, antibacterial activity and favorable strength and stiffness. However, its insufficient mechanical properties limits its feasibility and scope for clinical application, especially for bone scaffolds. The main purpose of the study is to explore the potential of incorporation of nanofillers into CS to enhance the mechanical properties for tissue engineering. In this work, nanodiamond (ND) is applied and studied due to its high surface to volume ratio, rich surface chemistry, high mechanical strength, and excellent biocompatibility. ND/CS nanocomposites with different diamond concentration from 1wt. % to 5wt. % were synthetized through a solution casting method. The microstructure and mechanical properties of the composites were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), and nanoindentation. Compared with pristine CS, the addition of ND resulted in a dramatic improvement of mechanical properties, including a 239%, 276%, 321%, 333%, and 343% increase in Young’s modulus and 68%, 96%, 114%, 118%, and 127% increase in hardness when ND amount is 1wt. %, 2wt. %, 3wt. %, 4wt. %, and 5wt. %, respectively. The strong interaction between ND surface groups and chitosan matrix is of great importance in changing polymer structure and improving mechanical properties. The cell viability and cytotoxicity of the nanocomposite were also studied using MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay. The results show that the addition of ND has no negative effect on cell viability and the nanocomposites have no cytotoxicity.