Fluorescent nanodiamond for nanotheranostic applications

The interest in application of nanodiamonds as nanotheranostics is increasing rapidly over recent years. The combination of properties, such as high refractive index, low toxicity, inertness, high carrier capacity and rich surface functionalities, as well as unique magneto-optical properties of the nitrogen-vacancy centre, renders fluorescent nanodiamonds superior to other nanomaterials as nanotheranostics. In this review, the current state of research on the applications of nanodiamonds as theranostics where they have been utilised in combination with both diagnostics/imaging and therapy simultaneously is discussed. Firstly, a brief introduction to the current knowledge about the synthesis and properties of nitrogen-vacancy centre in nanodiamonds is given. Then, the underlying principles that are responsible for the magneto-optical properties of nitrogen-vacancy centre are explained. The majority of theranostic applications of nanodiamonds rely on the judicious engineering of their surface with bioactive molecules. In the following section, methods of engineering the surface of nanodiamonds while preserving their colloidal stability and their implication on in vitro and in vivo biocompatibility are described. Subsequently, the recent developments and applications of nanodiamond conjugates as photo-theranostics and non-targeted and targeted theranostics are critically discussed. Co-delivery of specifically tailored nanodiamonds with both diagnostic/imaging and therapeutic features can considerably contribute towards nanotheranostics-based personalized medicine.