This review focuses on the development of multi-layer fullerenes, known as carbon nano-onions (CNOs). First, it briefly summarizes the most important synthetic pathways for their preparation and their properties and it gives the reader an update over new developments in the recent years. This is followed by a discussion of the published synthetic procedures for CNO functionalization, which are of major importance when elucidating future applications and addressing drawbacks for possible applications, such as poor solubility in common solvents. Finally, it gives an overview over the fields of application, in which CNO materials were successfully implemented.

Carbon based nanomaterials have emerged over the last few years as important agents for biomedical fluorescence and Raman imaging applications. These spectroscopic techniques utilize either fluorescently labelled carbon nanomaterials or the intrinsic photophysical properties of the carbon nanomaterial. In this review article we present the utilization and performance of several classes of carbon nanomaterials, namely carbon nanotubes, carbon nanohorns, carbon nanoonions, nanodiamonds and different graphene derivatives, which are currently employed for in vitro as well as in vivo imaging in biology and medicine. A variety of different approaches, imaging agents and techniques are examined and the specific properties of the various carbon based imaging agents are discussed. Some theranostic carbon nanomaterials, which combine diagnostic features (i.e. imaging) with cell specific targeting and therapeutic approaches (i.e. drug delivery or photothermal therapy), are also included in this overview.

Antimicrobial photodynamic inactivation (aPDI) employing the BODIPY-based photosensitizer 2,6-diiodo-1,3,5,7-tetramethyl-8-(N-methyl-4-pyridyl)-4,4′-difluoro-boradiazaindacene (DIMPy-BODIPY) was explored in an in vitro assay against six species of bacteria (eight total strains), three species of yeast, and three viruses as a complementary approach to their current drug-based or non-existent treatments. Our best results achieved a noteworthy 5–6 log unit reduction in CFU at 0.1 μM for Staphylococcus aureus (ATCC-2913), methicillin-resistant S. aureus (ATCC-44), and vancomycin-resistant Enterococcus faecium (ATCC-2320), a 4–5 log unit reduction for Acinetobacter baumannii ATCC-19606 (0.25 μM), multidrug resistant A. baumannii ATCC-1605 (0.1 μM), Pseudomonas aeruginosa ATCC-97 (0.5 μM), and Klebsiella pneumoniae ATCC-2146 (1 μM), and a 3 log unit reduction for Mycobacterium smegmatis mc²155 (ATCC-700084). A 5 log unit reduction in CFU was observed for Candida albicans ATCC-90028 (1 μM) and Cryptococcus neoformans ATCC-64538 (0.5 μM), and a 3 log unit reduction was noted for Candida glabrata ATCC-15545 (1 μM). Infectivity was reduced by 6 log units in dengue 1 (0.1 μM), by 5 log units (0.5 μM) in vesicular stomatitis virus, and by 2 log units (5 μM) in human adenovirus-5. Overall, the results demonstrate that DIMPy-BODIPY exhibits antiviral, antibacterial and antifungal photodynamic inactivation at nanomolar concentrations and short illumination times.

Carbon nano-onions (CNOs) are an exciting class of carbon nanomaterials, which have recently demonstrated a facile cell-penetration capability. In the present work, highly fluorescent boron dipyrromethene (BODIPY) dyes were covalently attached to the surface of CNOs. The introduction of this new carbon nanomaterial-based imaging platform, made of CNOs and BODIPY fluorophores, allows for the exploration of synergetic effects between the two building blocks and for the elucidation of its performance in biological applications. The high fluorescence intensity exhibited by the functionalized CNOs translates into an excellent in vitro probe for the high resolution imaging of MCF-7 human breast cancer cells. It was also found that the CNOs, internalized by the cells by endocytosis, localized in the lysosomes and did not show any cytotoxic effects. The presented results highlight CNOs as excellent platforms for biological and biomedical studies due to their low toxicity, efficient cellular uptake and low fluorescence quenching of attached probes.