Luminescent nanodiamonds as biolabels

<p dir="ltr">Conventional biological markers such as fluorophores are mostly used for bioimaging applications. However their limitations like cytotoxicity and lack of photostability have led to research on other optical nanoparticles. The work in this thesis focuses on material processing, characterisation and application of nanodiamonds for bioimaging applications.</p><p dir="ltr">Nanodiamond particles are biocompatible, chemically stable and have photostable optical defects in their core lattice. Nitrogen vacancy (NV) optical defects in nanodiamond have been focused in this work. The unique material, optical, spin and magnetic properties of nanodiamonds containing NV centres not only make them efficient fluorescent bio-labels but also allow them to be used for various quantum and nanoscale sensing applications.</p><p dir="ltr">In this thesis, I present a brief introduction about nanodiamond synthesis, its optical centres, properties and applications followed by the current challenges in developing the material for various applications. Post-synthesis nanodiamonds are mostly aggregated and have impurities. Therefore, improved material processing and surface functionalisation is important to develop nanodiamonds as a nanoscale sensor or as a bio-label. This work presents purification and processing methodology for isolating nanodiamonds of various sizes with desired surface profile for maximum brightness and photostability. A comparative brightness analysis for nanodiamonds of different sizes was performed to identify the most suitable size range for bioimaging applications at molecular level. The colloidal stability of nanodiamonds in ionic environment, such as that present in biological systems, was studied. Based on improved material processing, surface functionalisation, suitable size range and colloidal stability of nanodiamonds, they were efficiently conjugated to F-actin, opening up possibilities for their use as imaging labels that can selectively target biomolecule(s) of interest in complex biological systems.</p>