The unique properties of fluorescent nanodiamonds (FND):
- Intense fluorescence, quantifiable and unalterable over time, for permanent labelling, thanks to the NV centers (nitrogen-gap pair) present within the diamond mesh. These defects are also sensitive to magnetic fields causing a modulation of fluorescence intensity making FNDs magneto-optical sensors.
- Extremely resistant, inert, non-toxic and chemically modifiable on the surface.
Consequently, the use of FNDs as a marker in biology and medicine appears extremely interesting because it makes it possible to solve the photobleaching problem which is observed with most fluorophores, and extend the possibility to detect small magnetic fields with an extreme sensitivity. Their nanoscale size gives the advantage of an enormous surface that can serve as a platform for drug delivery while carrying the functionality necessary for targeted addressing. Fluorescent nanodiamonds are therefore capable of simultaneously presenting the three functions of addressing, detection and drug delivery.
Functionalization of FND for biology – medicine
Whatever the applications, the chemical functionalization of the nanodiamonds surface is necessary to (i) impede any aggregation in biological medium and (ii) monitor the interactions and/or the reactions with the biomolecules to be labeled in such a way as to obtain stable ND-biomolecule assemblies and thus to have a permanent marking or of a controlled duration. In addition, the biological activity of biomolecules attached to nanodiamonds must be retained, which implies that interactions with the nanoparticles must not interfere.
Fluorescent nanodiamonds for biodistribution studies
Thanks to their permanent fluorescence, FNDs representa tool of choice for particle tagging and monitoring in cell or living organisms and over extremely long periods as in the case of biodistribution studies in animals. We have thus developed the labeling of an alumina vaccine adjuvant by FND and demonstrated, from intramuscular injection, the effective translocation in the various organs (nodes, spleen, liver and brain) over time – up to 9 months of study.
Biodistribution of the FND:alumina vaccine adjuvant complex after its intramuscular injection into the anterior tibialis of mice. After 21 days post-injection, translocation occurred into the linguinal lymph nodes that appear almost empty (not shown) and the complex reached the liver (not shown), spleen and brain in the form of small clusters. Whatever the observations, Morin (aluminum-specific) labeling reveals that FNDand the aluminium adjuvant are co-localized (from Eidi et al., BMC 2015)
Fluorescent nanodiamonds for biomedical applications and to study neurodegeneration
For that purpose, the labeling of biomolecules (proteins, antibodies or nucleic acids) by a tracer such as FNDs is needed and requires the formation of a stable bond – chemical bond – between the two partners to retain the association. Thus, we developed different strategies for coupling nanodiamonds to biomolecules, including click-chemistry (financing linked to the FND maturation program, SATT Paris Saclay). This method has the particularity to use reactive groups that do not exist in the natural state in biological media and that react, in aqueous medium, quantitatively and specifically and, especially, without parasitic reaction with the surrounding environment.
Successful grafting of several proteins with FNDs and especially secondary antibody were obtained.
Yet we extend this tagging to proteins (TDP43, FUS) involved in neurodegenerative diseases to probe their aggregation in cells and animal models.