Carbon Dots are an emerging class of carbon-based nanoparticles, which since their discovery have attracted tremendous attention because of their exceptional fluorescent, chemical and mechanical properties as well as high photostability and biocompatibility. This unique combination of outstanding characteristics, together with the ease with which they can be synthesized, qualify carbon dots as highly promising materials for applications in electronics and biology, in particular, for biosensing, bioimaging, biotherapy and drug delivery. In this review, we present some of the most recent applications of carbon dots in biology and medicine, concentrating on their fluorescence properties, biocompatibility and efficiency; we also discuss how improvements could prompt their use in human studies. We illustrate how carbon dots, prepared through several facile and cost-effective methods by either the bottom-up or the top-down route, can be used for imaging cells and bacteria and as sensing probes of metal cations. Moreover, we explain how their astonishing versatility has given rise to new biotherapy methods especially in the field of cancer theranostics. GRAPHICAL ABSTRACT

Similar to carbon, germanium exists in various structures such as three-dimensional (3D) crystalline germanium and germanene, a two-dimensional (2D) germanium atomic layer. Regarding the electronic properties, they are either semiconductors or Dirac semimetals. Here, we report a novel highly conductive metallic state in thermally annealed germanane (hydrogen-terminated germanene, GeH), which shows a resistivity of ~10^-7 Ω∙m that is orders of magnitude lower than any other allotropes of germanium. By comparing the resistivity, Raman spectra, and thickness change measured by AFM, we suggest the highly conductive metallic state is associated with the dehydrogenation during heating, which likely transforms germanane thin flakes to multilayer germanene. In addition, weak anti-localization (WAL) is observed, serving as solid evidence for strong spin-orbit interaction (SOI) in germanane/germanene. Our study opens a possible new route to investigate the electrical transport properties of germanane/germanene, and the large SOI might provide the essential ingredients to access their topological states predicted theoretically.

The special electronic, optical, thermal, and mechanical properties of graphene resulting from its 2D nature, as well as the ease of functionalizing it through a simple acid treatment, make graphene an ideal building block for the development of new hybrid nanostructures with well-defined dimensions and behavior. Such hybrids have great potential as active materials in applications such as gas storage, gas/liquid separation, photocatalysis, bioimaging, optoelectronics, and nanosensing. In this study, luminescent carbon dots (C-dots) were sandwiched between oxidized graphene sheets to form novel hybrid multilayer films. Our thin-film preparation approach combines self-assembly with the Langmuir–Schaefer deposition and uses graphene oxide nanosheets as template for grafting C-dots in a bidimensional array. Repeating the cycle results in a facile and low-cost layer-by-layer procedure for the formation of highly ordered hybrid multilayers, which were characterized by photoluminescence, UV–visible, X-ray photoelectron, and Raman spectroscopies, as well as X-ray diffraction and atomic force microscopy.

In the present study, we developed novel β-glucosidase-based nano-biocatalysts for the bioconversion of oleuropein to hydroxytyrosol. Using non-covalent or covalent immobilization approaches, β-glucosidases from almonds and Thermotoga maritima were attached for the first time on oxidized and non-oxidized porous carbon cuboids (PCC). Various methods were used for the characterization of the bio-nanoconjugates, such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and fluorescence spectroscopy. The oxidation state of the nanο-support and the immobilization procedure play a key role for the immobilization efficiency or the catalytic activity of the immobilized β-glucosidases. The nano-biocatalysts were successfully used for the hydrolysis of oleuropein, which leads to the formation of its bioactive derivative, hydroxytyrosol (up to 2.4 g L⁻¹), which is a phenolic compound with numerous health benefits. The bio-nanoconjugates exhibited high thermal and operational stability (up to 240 h of repeated use), which indicated that they are efficient tools for various bio-transformations.

Here, we have studied the antibacterial effects of a newly synthesized carbon structure with excellent properties, named porous carbon cuboid (PCC) nanoparticles, upon Gram-negative Escherichia coli and Gram-positive Corynebacterium glutamicum bacterial cells and its algicidal effects upon Chlamydomonas reinhardtii microalgal cells. More specifically, the antibacterial properties of PCCs enriched with acid treatment (PCC-ox) or metal encapsulation (PCC-Cu and PCC-Ag) were investigated under various concentrations of PCCs and their interaction times. Additionally, the impact of PCCs upon microalgal growth was estimated by measuring the total chlorophyll level during their cultivation. As a result, E. coli and C. glutamicum were shown to be substantially inhibited by PCCs, depending on their special characteristics, dose, and bacterial strain. Moreover, it has been proven that the antibacterial effect is time-dependent. Growth of C. reinhardtii was inhibited by PCCs in a material-dependent manner, whereas PCC-Ag had the highest registered effect. These results suggest that PCCs could be used as an effective antibacterial material, although consideration should be given to issues involving the disposal of PCCs after usage, given their level of toxic effect on the environment.