Abstract
Fluorescent nanodiamond (FND) is a novel carbon based material that has drawn much attention in recent years due to its uniquely embedded defect centers named nitrogen-vacancy (N-V) centers. Most notable is the negatively charged nitrogen-vacancy (NV ̶ ) color center which emits a highly photostable far-red fluorescence emission. Since it does not photobleach or photoblink, it can be used to track for longer times. The FND also exhibits a very good biocompatibility and its surface can be easily functionalized through covalent or non-covalent interactions with biomolecules. The NV ̶ center has been used to sense environmental variables such as temperature and electric or magnetic fields by studying the shifts in their electronic transitions or spin transitions at electronic ground state. All these characteristics make FND a promising fluorescent probe for biological applications. Cell-to-cell communication is essential for the development and maintenance of multicellular organisms. Recently discovered membrane nanotubes (MNTs) are capable of creating intercellular communication pathways through which transport of proteins and other cytoplasmic components occurs. These cellular connections are very heterogeneous in both structure, function, and have been found to be formed in numerous cell types. MNTs are also known to participate in pathogenesis of many diseases such as Alzheimer’s, Parkinson’s and HIV. Hence, it is important to understand the dynamics of transport along these nanotubes and to explore the potential of MNTs as drug delivery channels. This doctoral thesis presents several applications of variously functionalized FNDs in membrane nanotubes. We applied protein functionalized FNDs as a photostable tracker, as well as a protein carrier, to illustrate the transport events in MNTs of human cells. Proteins, including bovine serum albumin and green fluorescent protein, were coated on 100-nm FNDs by physical adsorption. Then single-particle tracking of the bio-conjugates in the transient membrane connections was carried out by fluorescence microscopy. We observed different types of motions and velocity distribution of cargos that took takes place inside the MNTs. Our results demonstrate the promising applications of this novel carbon-based nanomaterial for intercellular delivery of biomolecular cargo down to the single-particle level. Further, we have studied the thermostability of both MNTs and cell membrane. We have developed gold nanorods (GNR) functionalized FNDs as a two-in-one optical nanodevice that can heat and sense the temperature simultaneously. We used all-optical method to study the nanothermometry of GNR-FNDs. We also demonstrated the photoporation on MNTs using GNR-FND nanohybrids to selectively deliver drugs to cytoplasm. Finally, we performed hyperlocalized hyperthermia on cell membrane for the treatment of cancer cell. During such a treatment, cancer cells can be killed selectively, while healthy cells remain unaffected. Our results demonstrate promising applications of this novel carbon-based nanomaterial for intercellular delivery of biomolecular cargo down to the single-particle level and a new paradigm for hyperthermia research and application.