Being sensitive to weak magnetic fields (nanotesla), these defects enable nanometer-scale resolution sensing and monitoring of proteins and nucleic acids in their natural environment. For example, tracking of the motion of a segment of a single protein molecule can be achieved with the nitroxide nuclear spin label detection by diamond located 10 nm away. This approach helps to understand the structure and dynamics of proteins in their natural environment. The exceptional photostability and non-blinking fluorescence of NV defects resulted in progress in stimulated emission depletion (STED) microscopy and other sub-diffraction resolution techniques. For example, NV center electron spin resonance probed with and switched on and off by microwave radiation, was super-imposed with their optical emission leading to subdiffraction limited resolution of NV centers in 2 NDs separated by only 22 nm within 7 × 9 ?m2field of view. NV defects in HPHTNDs and bulk diamonds have been used as precise temperature probes with potential in vivoapplications.In addition to fluorescence, NDs provide many other modalities, enabling their use in a broad array of biomedical imaging techniques from high resolution confocal fluorescent microscopy to nanoscale magnetometry and magnetic resonance imaging including clinically accessible imaging protocols, such as CT, MRI, and PET. These modalitiescombined with low production cost, facile surface modification, and low to no toxicity, open exciting avenues for nanodiamond particles as future theranostic platforms.Nanodiamonds have demonstrated significant promise both as cellular imaging and potential clinically-relevant imaging modalities. HPHT nanodiamond possess the advantage of being resistant to photobleaching, while still remaining biocompatible. This has enabled their widespread use in cellular uptake assays, and they have recently been explored in in-vivo studies as well. In addition to HPHT nanodiamond, the detonation of nanodiamond has also been explored as imaging agents. Examples include conjugating octadecylamine (ODA) to the nanodiamond surface, which resulted in a blue fluorescent nanodiamond. In addition, as nanodiamond development continues towards a translational roadmap, ND–gadolinium(III) (nanodiamond–Gd(III)) complexes have been synthesized for magnetic resonance imaging (MRI) applications. . Figure.7 shows the nanoparticles uptake into the cells.