Nanodiamonds Application in Cancer Imaging and Therapy
In modern society with the rapid development of the medical level, cancer is still a global disease. Various cancers seriously threaten human health, and the number of people dying from cancer is increasing every year. Cancer detection and the timing of treatment are critical to the success of a cancer cure. In the treatment of cancer, it is very important and difficult to locate and track cancer cells. Traditional organic molecules that can be used as fluorescent probes often need to be coupled with other molecules and show certain toxicity. Traditional fluorescent protein-based fluorescent probes tend to have larger molecules and lower signals. Recent studies have shown that some non-metallic materials exhibit fluorescence properties, which have excellent application prospects in cell fluorescence imaging. Nanodiamond is one of these materials, which emits fluorescence under a certain excitation wavelength of light, and the fluorescence emitted has good stability.
Nanodiamonds (ND) are single crystal diamonds with carbon as the basic component, which have high physical and chemical properties. These are nanoscale versions of sp3 carbon, while other carbon nanotubes and fullerenes are sp2 configurations. The average particle size of diamond nanoparticles is 4-5 nm. Depending on the primary particle size, ND can be classified as nanocrystalline particles (1 to ≥150 nm) and ultra-nanocrystalline particles (2-10 nm).
Fig. 1 Schematic representation of nanodiamond classification (Chauhan, S.; et al. 2020).
Optical Properties of Fluorescent Nanodiamonds (FND)
Nitrogen is the most common impurity in diamonds, incorporated into the crystal lattice in the form of isolated substitute nitrogen atoms or two nearest neighbor substitute nitrogen atoms and numerous other nitrogen-containing defects. The vacancies trapped by nitrogen atoms form different color centers, depending on the type of N state in the diamond. Nitrogen-vacancy (NV) defects are responsible for the diamond's red/near-infrared fluorescence, and nitrogen-vacancy-nitrogen (NVN) color centers have bright green photoluminescence. NV centers are defects in diamonds formed by substituted nitrogen atoms and adjacent vacancies, while NVN centers consist of nitrogen-vacancy-nitrogen complexes. The optical properties of NV centers are well suited for applications in cancer cell imaging and tracking, with optical excitation at 490-560 nm and emission at 637-800 nm, away from most autofluorescent cellular components.
Inhibition of Tumour Cell Migration by Nanodiamond
Studies have shown that carboxylated nanodiamonds can enhance the adhesion of tumor cells to the substrate, resulting in restricted cell motility. In terms of molecular mechanism, carboxylated nanodiamonds can down-regulate the expression of N-cadherin and vimentin, up-regulate the expression of E-cadherin, and reverse the EMT process through the TGF-β signaling pathway. Phalloidin staining experiments confirmed that carboxylated nanodiamonds can damage the assembly of F-actin cytoskeleton, reduce the formation of stress fibers and lamellipodia, and inhibit the migration of tumor cells. The inhibitory effect of carboxylated nanodiamonds on tumor metastasis in vivo was verified using a mouse lung metastasis model.
Nanodiamonds have been favored in bioimaging, single-photon sources, and drug delivery due to their excellent optical properties, such as high photostability, easy surface functionalization, water dispersibility, good biocompatibility, and inertness. In the future, nanodiamonds can be used to label protein molecules for fluorescence microscopy imaging to track and locate cancer cells, and can be a new inhibitor of tumor cell migration and play an active role in regulating cell behavior.
References
- Chauhan, S.; et al. Nanodiamonds with powerful ability for drug delivery and biomedical applications: Recent updates on in vivo study and patents. Journal of Pharmaceutical Analysis. 2020, 10(1): 1-12.
- Guo Q.; et al. Nanodiamonds inhibit cancer cell migration by strengthening cell adhesion: implications for cancer treatment. ACS Applied Materials & Interfaces. 2021, 13(8): 9620-9.
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