(Invited) Carbon Nano Onions for Biomedical Applications
Authors: Giordani Silvia 
Published: May 2020

Carbon-based nanomaterials have emerged as platforms for biomedical applications because of their low toxicity and ability to be internalized by cells [1]. The development of imaging probes and drug delivery devices based on carbon nanomaterials for biomedical studies requires the understanding of their biological response as well as the efficient and safety exposition of the nanomaterial to the cell compartment where it is designed to operate.
Multi-shell fullerenes, also known as carbon nano-onions (CNOs) are structured by concentric shells of carbon atoms and display several unique properties, such as a large surface area to volume ratio, low density and a graphitic multilayer morphology [2]. In my research group we have developed a versatile and robust approach for the functionalisation of CNOs, involving the facile introduction of a number of simple functionalities onto their surface. Our results have shown that chemical functionalization of the CNOs dramatically enhance their solubility and reduce their inflammatory properties in vitro and in vivo [3]. We reported the absence of adverse effects induced by CNOs on short and long term toxicity in Hydra [4] and in zebrafish [5] suggesting a reasonable degree of biosafety of this new class of nanomaterials. We have developed intracellular imaging systems based on CNOs functionalised with BODIPY derivatives [6], with special attention to the biologically important near-infra red (NIR) region [7] and pH dependent fluorescence on-off switching [8]. The on/off emission of the fluorescent CNOs is fast and reversible both in solution and in vitro, making this nanomaterial suitable as pH-dependent probes for diagnostic applications [8].
We have also developed a synthetic multi-functionalisation strategy for the introduction of different functionalities (receptor targeting unit and imaging unit) onto the surface of the CNOs The modified CNOs display high brightness and photostability in aqueous solutions and their selective and rapid uptake in two different cancer cell lines without significant cytotoxicity is demonstrated. The localization of the functionalized CNOs in late-endosomes cell compartments is revealed by a correlative approach with confocal and transmission electron microscopy [9].
To probe the possible applications of CNOs as a platform for therapeutic and diagnostic interventions on CNS diseases, we injected fluorescent CNOs in vivo in mice hippocampus. We analyzed ex vivo their diffusion within brain tissues and their cellular localization by confocal and electron microscopy. The subsequent fluorescent staining of hippocampal cells populations indicates they efficiently internalize the nanoparticles. Furthermore, the inflammatory potential of the CNOs injection was found comparable to sterile vehicle infusion, and it did not result in manifest neurophysiological and behavioral alterations of hippocampal-mediated functions [10]. These results encourage further development as brain disease-targeted diagnostics or therapeutics nanocarriers.

References

[1] J. Bartelmess et al., Chem Soc Rev 44 (14), 115 (2015).
[2] S. Giordani et al., Current Medicinal Chemistry, in press (2019).
[3] M. Yang et al., Small 9, 4194 (2013).
[4] V. Marchesano et al., Nanomaterials 5, 1331 (2015).
[5] M. d'Amora et al., Scientific Reports 6, 33923 (2016).
[6] J. Bartelmess et al. Nanoscale 6, 13761 (2014).
[7] S. Lettieri et al., RSC Advances 7, 45676 (2017).
[8] S. Lettieri et al., Beilstein J. Nanotechnol. 8, 1878 (2017).
[9] M. Frasconi et al., Chem Eur J 21 (52), 19071 (2015).
[10] M. Trusel et al., ACS Appl. Mat. & Inter. 10 (20), 16952 (2018).

Figure 1