Fluorescent enhancement of the nitrogen vacancy center in nanoscale diamond for bioimaging applications

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Project Summary/Abstract In this body of work the Wolcott laboratory will develop chemical methodologies for the functionalization of nanoscale diamond with the aim of increasing the fluorescent rate of the nitrogen vacancy center (NVC) via plasmonics. We are focusing our expertise to understand chemical reactivity at the high-pressure high- temperature diamond surface and investigate the mechanisms for diamond-metal nanostructure self-assembly. Advancements in bioimaging with fluorescent nanodiamonds (FNDs) are hindered by a lack of robust chemistry to modify their surface. Further, no advances for increasing the NVC fluorescent rate have been realized. In total, these challenges have resulted in poor colloidal stability, poor targeting in staining protocols and no simple routes to enhance FND emission rates. We will address these challenges to advance the surface chemistry of nanoscale diamond, build coherent models of chemical reactivity and increase the efficacy for self-assembly with metallic nanostructures. The nitrogen vacancy center in 25-100 nm crystallites have shown fluorescent enhancement, but only with tedious movement of these structures by atomic force microscopy which is incompatible with cell imaging. A major goal of the study is to understand how tuning the surface chemistry will drive self-assembly, how dielectric layer thickness effects fluorescent rates and the production of FND-metallic constructs with robust properties for bioimaging. Further, we envision using these FND constructs in fluorescent imaging studies with pancreatic cancer cell lines. Our aims include both fundamental studies and applied fluorescence imaging investigations. The goals of the proposed work include: 1) modification of the FND surface with wet chemical and gas phase chemistry, (2) application of the modified FND for metallic nanostructure assembly and (3) the fundamental mechanisms of NVC fluorescence enhancement for imaging applications. Our surface chemistry will focus on covalent bond formation of low-Z elements such as nitrogen and silicon oxide to the ND surface. To probe the surface we will use overlapping techniques that are laboratory and synchrotron-based spectroscopies. Techniques include dynamic light scattering, FTIR, wavelength dependent X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS). Surface information will then be used to direct our chemical methodology and protocol development. The covalent moieties will then act as the molecular anchors to drive their assembly with metal nanostructures and to grow metallic shells. FND emission properties will be investigated with confocal microscopy to determine fluorescent rates and radiative lifetimes. Finite-difference time-domain simulations will guide our chemistry and establishes a target of a 150x fold increase for the NVC fluorescent rate. This work will impact fundamental and applied research where the NVC is used for magnetic and electric field imaging, thermometry and long-term bioimaging applications. PI-Wolcott is an expert in diamond surface chemistry and the use of nanoparticles for biological staining. This project will be supported by the active collaborations with nanomaterial expert Prof. Nicholas Melosh at Stanford University and surface scientist Dr. Dennis Nordlund at the Stanford Synchrotron Radiation Lightsource (SSRL). The prime location of San Jose State University (SJSU) in the Bay Area provides unique opportunities for science to be accomplished at near-by research centers such as SSRL and The Molecular Foundry at Lawrence Berkeley National Laboratory. A highly motivated team of undergraduate researchers in the Wolcott laboratory at SJSU are taking full advantage of this environment and are advancing the initial aims of this proposal as detailed in the Research Strategy.