Understanding the nanoscale adhesion forces between the fungal pathogen Candida albicans and antimicrobial zinc-based layered double hydroxides using single-cell and single-particle force spectroscopy.

Antifungal resistance has become a very serious concern, and Candida albicans is considered one of the most opportunistic fungal pathogens responsible for several human infections. In this context, the use of new antifungal agents such as zinc-based layered double hydroxides to fight such fungal pathogens is considered one possible means to help limit the problem of antifungal resistance. In this study, we show that ZnAl LDH nanoparticles exhibit remarkable antifungal properties against C. albicans and cause serious cell wall damage, as revealed by growth tests and atomic force microscopy (AFM) imaging. To further link the antifungal activity of ZnAl LDHs to their adhesive behaviors toward C. albicans cells, AFM-based single-cell spectroscopy and single-particle force spectroscopy were used to probe the nanoscale adhesive interactions. The force spectroscopy analysis revealed that antimicrobial ZnAl LDHs exhibit specific surface interactions with C. albicans cells, demonstrating remarkable force magnitudes and adhesion frequencies in comparison with non-antifungal negative controls, e.g., Al-coated substrates and MgAl LDHs, which showed limited interactions with C. albicans cells. Force signatures suggest that such adhesive interactions may be attributed to the presence of agglutinin-like sequence (Als) adhesive proteins at the cell wall surface of C. albicans cells. Our findings propose the presence of a strong correlation between the antifungal effect provided by ZnAl LDHs and their nanoscale adhesive interactions with C. albicans cells at both the single-cell and single-particle levels. Therefore, ZnAl LDHs could interact with C. albicans fungal pathogens by specific adhesive interactions through which they adhere to fungal cells, leading to their damage and subsequent growth inhibition.

Heterogeneous Photoredox Catalysis Based on Silica Mesoporous Material and Eosin Y: Impact of Material Support on Selectivity of Radical Cyclization.

Heterogenization of the photocatalyst appears to be a valuable solution to reach sustainable processes. Rapid and efficient synthesis of supported photocatalyst is still a remaining challenge and the choice of the support material is crucial. The present study aims at preparing a new generation of hybrid inorganic/organic photocatalysts based on silica mesoporous material and Eosin Y. These results highlight the influence of non-covalent interactions between the material support and the reagent impacting the selectivity of the reaction.

Understanding the role of surface interactions in the antibacterial activity of layered double hydroxide nanoparticles by atomic force microscopy.

Understanding the mechanisms of the interactions between zinc-based layered double hydroxides (LDHs) and bacterial surfaces is of great importance to improve the efficiency of these antibiotic-free antibacterial agents. In fact, the role of surface interactions in the antibacterial activity of zinc-based LDH nanoparticles compared to that of dissolution and generation of reactive oxygen species (ROS) is still not well documented. In this study, we show that ZnAl LDH nanoparticles exhibit a strong antibacterial effect against Staphylococcus aureus by inducing serious cell wall damages as revealed by the antibacterial activity tests and atomic force microscopy (AFM) imaging, respectively. The comparison of the antibacterial properties of ZnAl LDH nanoparticles and micron-sized ZnAl LDHs also demonstrated that the antibacterial activity of Zn-based LDHs goes beyond the simple dissolution into Zn2+ antibacterial ions. Furthermore, we developed an original approach to functionalize AFM tips with LDH films in order to probe their interactions with living S. aureus cells by means of AFM-based force spectroscopy (FS). The force spectroscopy analysis revealed that antibacterial ZnAl LDH nanoparticles show specific recognition of S. aureus cells with high adhesion frequency and remarkable force magnitudes. This finding provides a first insight into the antibacterial mechanism of Zn-based LDHs through direct surface interactions by which they are able to recognize and adhere to bacterial surfaces, thus damaging them and leading to subsequent growth inhibition.

Direct contact, dissolution and generation of reactive oxygen species: How to optimize the antibacterial effects of layered double hydroxides.

Infections by pathogenic bacteria have been threatening several fields as food industries, agriculture, textile industries and healthcare products. Layered double hydroxides materials (LDHs), also called anionic clays, could be utilized as efficient antibacterial materials due to their several interesting properties such as ease of synthesis, tunable chemical composition, biocompatibility and anion exchange capacity. Pristine LDHs as well as LDH-composites including antibacterial molecules and nanoparticles loaded-LDHs were proven to serve as efficient antibacterial agents against various Gram-positive and Gram-negative bacterial strains. The achieved antibacterial effect was explained by the following mechanisms: (1) Direct contact between the materials and bacterial cells driven by electrostatic interactions between positively charged layers and negatively charged cell membranes, (2) Dissolution and gradual release over time of metallic ions or antibacterial molecules, (3) Generation of reactive oxygen species.