| Fluorescent Nanodiamond (FND) offers a promising platform for many therapeutic applications involving drug and gene delivery, optical agents for bioimaging and labeling, and molecular detection. This is due to the potential to incorporate photostable luminescent vacancy-related defects into sub-10 nm diamond crystals which are biologically compatible and easy to functionalize. Moreover, the development of future nanoscale devices and arrays based on nanodiamonds (NDs) will require precise spatial control. Hence, the direct placement and manipulation (control of size, shape and chemical functionality) of brightly fluorescent sub-10 nm NDs offers potential for highly localized /specific imaging and sensing, while also providing the potential for controlled therapeutic dosing and release rate.;As the size of NDs gets smaller (with a corresponding reduced number of defect centers), the ability to maintain a high fluorescent yield is extremely important, especially biomedical imaging and detection. One focus of this dissertation is to develop fluorescent ND as a near ideal luminescent center for biomedical applications by incorporation of silicon vacancy (Si -V) defect centers as a viable alternative to nitrogen-vacancy (NV) defects using microwave plasma chemical vapor deposition (MPCVD) . Using this technique, we aim to create discrete, clinically relevant sub-10 nm size NDs exhibiting bright fluorescence in the far-red emission spectrum. The resulting narrow-band room temperature photoluminescence is intense, and readily observed even for weakly agglomerated sub-10 nm size diamond. This is in contrast to the well-studied nitrogen-vacancy center in diamond which has luminescence properties that are strongly dependent on particle size, with low probability for incorporation of centers in sub-10 nm crystals and that suffer from low brightness in this size regime. The potential for further enhancement of the room temperature luminescence intensity from Si-V centers in nanodiamonds of averaged size 255 nm is demonstrated through controlled nitrogen co -doping by adding varying amounts of N2in a H2+CH4 feedgas mixture during CVD treatment. The strong dependence of Si-V luminescence intensity on nitrogen co-doping is described in terms of an associated evolution in diamond morphology and quality along with the expected influence of nitrogen on the energy of the defects in the diamond bandgap. At low levels, isolated substitutional nitrogen in {100} growth sectors is believed to act as a donor to increase the population of optically active (Si-V)- at the expense of optically inactive Si-V defects, thus increasing the observed luminescence from this center. At higher levels, clustered nitrogen leads to deterioration of diamond quality with twinning and increased surface roughness primarily on {111} faces, leading to a quenching of the Si-V luminescence.;To further improve the applicability of FNDs, the scanning probe based "Dip Pen" nano-lithography" (DPN) technique was used to determine the feasibility to directly place functionalized/ fluorescent NDs onto SiO2 surface, with the ultra-high resolution offered via an atomic force microscope tip. In this way, we explored the mechanism of ink transport, the development of a suitable ND ink to enable efficient printing, and the influence that various parameters (such as temperature, relative humidity, dwell time etc.) have on the DPN printing process. We determined that the precision patterning of nanodiamonds was made possible by DPN using electrostatically driven transfer of nanodiamond from "inked" cantilevers to a hydrophilic SiO 2 substrate. The potential to incorporate photostable Si-V luminescent defect centers into precisely patterned nanoscale diamond particles was realized by subsequent chemical vapor deposition treatment. The results obtained in this research represent a significant step towards resolving extended intracellular biological processes (which require precise spatial control as well as a photostable luminescent center). In addition, our results point the way toward better control of therapeutic dosage and release in targeted drug delivery as well as enhanced molecular detection and standardization.;We anticipate that the intense and photostable far-red luminescence (∼738 nm) observed from Si-V defect centers incorporated into spatially arranged nanodiamonds will address the current limitations associated with nanoparticle agglomeration, photobleaching of conventional fluorophores, toxicity and photoblinking of quantum dots, and interference from cell autofluorescence in biological tissues. Potential applications include molecular sensing, single-particle tracking, and nano-manufacturing of hybrid devices containing precisely placed drug-laden ND for slow-release kinetics.;Keywords: fluorescent nanodiamond (FND), scanning probe lithography, Raman mapping, atomic force microscopy, room temperature photoluminescence, biosensing-array, silicon vacancy (Si-V) defect centers, nitrogen vacancy (NV) defect centers, microwave plasma chemical vapor deposition (MPCVD. |
