Therapeutic options for the highly pathogenic human coronavirus (HCoV) infections are urgently needed. Anticoronavirus therapy is however challenging, as coronaviruses are biologically diverse and rapidly mutating. In this work, the antiviral activity of seven different carbon quantum dots (CQDs) for the treatment of human coronavirus HCoV-229E infections was investigated. The first generation of antiviral CQDs was derived from hydrothermal carbonization of ethylenediamine/citric acid as carbon precursors and postmodified with boronic acid ligands. These nanostructures showed a concentration-dependent virus inactivation with an estimated EC 50 of 52 ± 8 μg mL −1 . CQDs derived from 4-aminophenylboronic acid without any further modification resulted in the second-generation of anti-HCoV nanomaterials with an EC 50 lowered to 5.2 ± 0.7 μg mL −1 . The underlying mechanism of action of these CQDs was revealed to be inhibition of HCoV-229E entry that could be due to interaction of the functional groups of the CQDs with HCoV-229E entry receptors; surprisingly, an equally large inhibition activity was observed at the viral replication step.

Colloidal semiconductor quantum dots are fluorescent nanocrystals exhibiting exceptional optical properties, but their emission intensity strongly depends on their charging state and local environment. This leads to blinking at the single-particle level or even complete fluorescence quenching, and limits the applications of quantum dots as fluorescent particles. Here, we show that a single quantum dot encapsulated in a silica shell coated with a continuous gold nanoshell provides a system with a stable and Poissonian emission at room temperature that is preserved regardless of drastic changes in the local environment. This novel hybrid quantum dot/silica/gold structure behaves as a plasmonic resonator with a strong Purcell factor, in very good agreement with simulations. The gold nanoshell also acts as a shield that protects the quantum dot fluorescence and enhances its resistance to high-power photoexcitation or high-energy electron beams. This plasmonic fluorescent resonator opens the way to a new family of plasmonic nanoemitters with robust optical properties.

The fabrication of van der Waals heterostructures, artificial materials assembled by individual stacking of 2D layers, is among the most promising directions in 2D materials research. Until now, the most widespread approach to stack 2D layers relies on deterministic placement methods, which are cumbersome and tend to suffer from poor control over the lattice orientations and the presence of unwanted interlayer adsorbates. Here, we present a different approach to fabricate ultrathin heterostructures by exfoliation of bulk franckeite which is a naturally occurring and air stable van der Waals heterostructure (composed of alternating SnS2-like and PbS-like layers stacked on top of each other). Presenting both an attractive narrow bandgap (<0.7 eV) and p-type doping, we find that the material can be exfoliated both mechanically and chemically down to few-layer thicknesses. We present extensive theoretical and experimental characterizations of the material's electronic properties and crystal structure, and explore applications for near-infrared photodetectors.

High colloidal stability in aqueous conditions is a prerequisite for fluorescent nanocrystals, otherwise known as "quantum dots", intended to be used in any long-term bioimaging experiment. This essential property implies a strong affinity between the nanoparticles themselves and the ligands they are coated with. To further improve the properties of the bidentate monozwitterionic ligand previously developed in our team, we synthesized a multidentate polyzwitterionic ligand, issued from the copolymerization of a bidentate monomer and a monozwitterionic one. The nanocrystals passivated by this polymeric ligand showed an exceptional colloidal stability, regardless of the medium conditions (pH, salinity, dilution, and biological environment), and we demonstrated the affinity of the polymer exceeded by 3 orders of magnitude that of the bidentate ligand (desorption rates assessed by a competition experiment). The synthesis of the multidentate polyzwitterionic ligand proved also to be easily tunable and allowed facile functionalization of the corresponding quantum dots, which led to successful specific biomolecules targeting.

Long-term inspection of biological phenomena requires probes of elevated intra- and extracellular stability and target biospecificity. The high fluorescence and photostability of quantum dot (QD) nanoparticles contributed to foster their promise as bioimaging tools that could overcome limitations associated with traditional fluorophores. However, QDs' potential as a bioimaging platform relies upon a precise control over the surface chemistry modifications of these nano-objects. Here, a zwitterion-vinylimidazole block copolymer ligand was synthesized, which regroups all anchoring groups in one compact terminal block, while the rest of the chain is endowed with antifouling and bioconjugation moieties. By further application of an oriented bioconjugation approach with whole IgG antibodies, QD nanobioconjugates were obtained that display outstanding intra- and extracellular stability as well as biorecognition capacity. Imaging the internalization and intracellular dynamics of a transmembrane cell receptor, the CB1 brain cannabinoid receptor, both in HEK293 cells and in neurons, illustrates the breadth of potential applications of these nanoprobes.

The physical properties of ultrathin transition metal dichalcogenides (2D-TMDCs) make them promising candidates as active nanomaterials for catalysis, optoelectronics, and biomedical applications. Chemical modification of TMDCs is expected to be key in modifying/adding new functions that will help make such promise a reality. We present a mild method for the modification of the basal planes of 2H-MoS2 and WS2. We exploit the soft nucleophilicity of sulfur to react it with maleimide derivatives, achieving covalent functionalization of 2H-TMDCs under very mild conditions. Extensive characterization proves that the reaction occurs through Michael addition. The orthogonality and versatility of the thiol–ene “click” chemistry is expected to allow the à la carte chemical manipulation of TMDCs.

In clinical diagnostics, homogeneous time-resolved (TR) FRET immunoassays are used for fast and highly sensitive detection of biomarkers in serum samples. The most common immunoassay format is based on europium chelate or cryptate donors and allophycocyanin acceptors. Replacing europium donors with terbium complexes and the acceptors with QDs offers large photophysical advantages for multiplexed diagnostics, because the Tb-complex can be used as FRET donor for QD acceptors of different colors. Water-soluble and biocompatible QDs are commercially available or can be synthesized in the laboratory using many available recipes from the literature. Apart from the semiconductor material composition, an important aspect of choosing the right QD for TR-FRET assays is the thickness of the QD coating, which will influence the photophysical properties and long-term stability as well as the donor-acceptor distance and FRET efficiency. Here we present a detailed time-resolved spectroscopic study of three different QDs with an emission maximum around 605 nm for their application as FRET acceptors (using a common Tb donor) in TR-bioassays: (i) Invitrogen/Life Technologies Qdot605, (ii) eBioscience eFluorNC605 and iii) ter-polymer stabilized CdSe/CdS/ZnS QDs synthesized in our laboratories. All FRET systems are very stable and possess large Förster distances (7.4-9.1 nm), high FRET efficiencies (0.63-0.80) and low detection limits (0.06-2.0 pM) within the FRET-bioassays. Shapes, sizes and the biotin/QD ratio of the biocompatible QDs could be determined directly in the solution phase bioassays at subnanomolar concentrations. Both commercial amphiphilic polymer/lipid encapsulated QDs and self-made ligand-exchanged QDs provide extremely low detection limits for highly sensitive TR-FRET bioassays.

Two-dimensional semiconducting materials are particularly appealing for many applications.Although theory predicts a large number of two-dimensional materials, experimentally only a few of these materials have been identified and characterized comprehensively in the ultrathin limit. Lead iodide, which belongs to the transition metal halides family and has a direct bandgap in the visible spectrum, has been known for a long time and has been well characterized in its bulk form. Nevertheless, studies of this material in the nanometer thickness regime are rather scarce. In this article we demonstrate an easy way to synthesize ultrathin, highly crystalline flakes of PbI2 by precipitation from a solution in water. We thoroughly characterize the produced thin flakes with different techniques ranging from optical and Raman spectrosThis is the post-peer reviewed version of the following article: R. Frisenda et al., "Characterization of highly crystalline lead iodide nanosheets prepared by room-temperature solution processing" Nanotechnology (2017) https://dx.doi.org/10.1088/1361-6528/aa8e5c 2 copy to temperature-dependent photoluminescence and electron microscopy. We compare the results to ab initio calculations of the band structure of the material. Finally, we fabricate photodetectors based on PbI2 and study their optoelectronic properties.