Fluorescent nanodiamonds are ideal reagents for long-term cell labeling and tracking, as well as for in vivo biomedical imaging. The most common type of fluorescent nanodiamond is the Nitrogen-Vacancy Center (NV-center), but Cymaris currently has a number of other diamond color centers under development that may also have use in the biological realm. Fluorescent nanodiamonds (20 to 100 nm) have been found to be safe and non-toxic in vitro and are taken up by cells non-specifically into the cytoplasm. Their surface chemistry is robust, which allows for a variety of coupling strategies and permits attachment of a number of different molecules. Due to their safety, and to their optical and magnetic properties, fluorescent nanodiamonds can compete with and may surpass other materials that are used in the biological marketplace, such as organic dyes, quantum dots, and gold nanoparticles.
For use in biological applications, diamonds must contain ensembles of at least 10 or more color centers in order to provide the high luminescence required during biomedical imaging. This differentiates them from the single-photon emitters required for use in photophysics. In particular, nanodiamonds that emit fluorescence in the NIR region between 650 to 950 (NIR I) and between 1000-1350 nm (NIR II) are of special interest for in vivo imaging applications. Emissions in this window are biologically transparent and experience limited or no interference from water and tissue/blood components.
Both fluorescent and non-fluorescent nanodiamonds have been tested in animal models and primitive organisms with promising results. Non-fluorescent nanodiamonds are currently being developed as drug delivery vehicles; as an example, doxorubicin has been adsorbed to the surface of nanodiamonds for use in cancer treatment. Columbus Nanoworks is currently exploring the use of fluorescent nanodiamonds for use in targeted, and potentially tracked, drug delivery, and for cell tracking applications as well.