| Summary: | 博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 107 === Fluorescent nanodiamond (FND) possesses nitrogen vacancy centers NVs, can fluoresces in broad wavelength in the regime from 550 nm to 900 nm after excited by a green yellow light. The fluorescence generated from the NVs of the FND is very suitable for long time observation because it is stable and immune to both photo-bleaching and photo-blinking issues. Fluorescent diamond (FD) fabrication contains three processes. Firstly, the type Ib diamond containing 100 to 200 ppm nitrogen atoms is widely used to be the starting material. Secondly, it is through high energy electron (e−, beta particle), proton (H+) or helium (He+) irradiation to create vacancies inside diamonds. Finally, an annealing process at typically elevated 800 oC for two hours is applied to facilitate the created mobile vacancies to be effectively captured by neighboring nitrogen atoms to perform nitrogen vacancy centers (NVs). In addition, the NVs can be classified into a neutral type NV0 with the energy gap 2.156 eV, or a negatively charged type NV− with the energy gap 1.945 eV. Furthermore, the artificial FND,
In recent studies, the fluorescence intensity of the fluorescent diamonds always drops dramatically as the size of the fluorescent diamonds is decreased, especially in nanometer scale. Actually, the vacancies embed carbon lattices site will migrate during the vacuum annealing process of the FND fabrication. Not every vacancy in the outermost diamond shell layer will be captured by the neighboring nitrogen atoms to perform the NV. Once the migratory vacancy reaches to the diamond surface, the migratory vacancy will become a surface void or a part of ambient in the air. In this dissertation, we are the first one to propose an effective NV volume ratio (Veff) of FND hypothesis. If the outermost shell layer of the FND in various sizes is lack of NVs and this shell layer has a thickness D from its surface, the fluorescence intensity of the FND would drop dramatically as the FND size is decreased. In this dissertation, an equation is developed to perform the Veff of the FND in various sizes. If the thickness D of the FND is 10 nm, the Veff of 100 nm FND is 51.2%. When the FD diameter is 1 µm, the Veff would be up to 94.1%.
In the past decades, localized surface plasmon resonance (LSPR) has been widely employed to enhance Raman signals or imaging contrast. LSPR is a powerful technique for concentrating an electromagnetic field at localized hot spots; the generated hot spots are frequently used for both metal-enhanced fluorescence (MEF) and surface-enhanced Raman scattering (SERS). However, the coverage of the MEF method is not larger enough to cover the three dimensional FND particle, and the enhancement of the fluorescence intensity is limited. This is coherent with our Veff of the FND hypothesis. Because a simple two–layer structural nanocavity is promising for easily available, enlarging the coverage, and manipulating the space electric-field power density above the nanocavity. The first part of this dissertation, we present a simple nanocavity structure that provide a large region for efficient enhancement of fluorescence that can cover most 100–nm FNDs. By tuning the thickness of the capping SiO2 layer of the Al/SiO2 nanocavities, the distributions of both the spatial and spectral electric field intensities of the FNDs could be controlled and manipulated. To enhance the fluorescence intensity from the NV− centers of the FNDs, we designed an Al/70–nm SiO2 nanocavity to function at excitation and emission wavelengths of 633 and 710 nm, respectively, allowing the NV− centers to be excited efficiently; as a result, we achieved an enhancement in fluorescence intensity of 11.2–fold.
In the past decades, FND has been widely investigated and applied in the optical and biological field. Comparing to FND, there are few studies about the brilliant FMDs. The second part of this dissertation, we adopt a non-destructive optical method to inspect the localized quality of an individual FMD particle. While using a 532–nm excitation laser source, the fluorescence intensity of FMD is tremendous and it’s hard to distinguish fluorescence and Raman signals simultaneously. Occasionally, we adopted a 785–nm laser to excite the NVs− abundant FMD, and then first obtained both the broadening fluorescent signals in the regime from 620 to 900 nm as well as diamond Raman peak at 1332 cm−1 in one spectrum. To address this issue with precision, in this study, we first utilized the fluorescence intensity of the FMD to reference its’ Raman peak at 1332–cm−1 intensity, and the localized surface fluorescent quality of an individual FMD could be fast inspected.
This dissertation also characterized the optical properties of the brilliant fluorescent microdiamonds (FMDs, diameter ~ 400 µm) and explored their potential use as fiducial markers for image-guided photothermal therapy. Although, the strong light scattering generated by the tissue with incident light may result in the image of FMD blurred, and deteriorated markedly with the increase of the phantom thickness. We first applied the FMDs for deep-tissue imaging with a 637–nm laser for the excitation and obtained spatially resolved fluorescence images of the individual particles in chicken breast tissue of ~3 mm in thickness. To well use the superior thermal conductivity property of diamond for image-guided therapy, the surface-functionalized FMDs were then decorated with hollow gold nanoparticles (HGNs). HGNs performed outstanding light-to-heat conversion. Through Mie theory calculation, one–tenth quantities of HGNs could absorb most of the 798-nm light. Through SEM inspection, up to 4 × 107 HGNs were estimated to be attached to a single FMD particle. A temperature rises of more than 20 °C was achievable when five HGN-FMDs particles were embedded 2 mm deep in chicken breast and irradiated by a 785–nm laser at a power density of 2.4 W/cm2. No fluorescence decay was observed for the FMDs over 30–min excitation, allowing repetitive and precise localization of the hybrid photothermal agents in tissue with submillimeter resolution. Our results highlight the promising use of NV-containing diamond microcrystals in conjugation with gold nanoparticles for local hyperthermia and inspection applications.
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