Physical mechanisms driving the reversible aggregation of Staphylococcus aureus and response to antimicrobials.

Formation of non-sessile, auto-aggregated cells of Staphylococcus aureus contributes to surface colonization and biofilm formation, hence play a major role in the early establishment of infection and in tolerance to antimicrobials. Understanding the mechanism of aggregation and the impact of aggregation on the activity of antimicrobials is crucial in achieving a better control of this important pathogen. Previously linked to biological phenomena, physical interactions leading to S.

Colorimetric detection of residual quaternary ammonium compounds on dry surfaces and prediction of antimicrobial activity using bromophenol blue.

Controlling and monitoring the residual activity of quaternary ammonium compounds (QACs) are critical for maintaining safe yet effective levels of these agents in the environment. This study investigates the utility of bromophenol blue (BPB) as a safe, rapid and user-friendly indicator to detect in situ residual QACs dried on hard, non-porous surfaces, as well a means to assess their antimicrobial efficacy. At pH 7, BPB has a purple colour which turns blue upon its complexation with QACs such as didecyldimethylammonium chloride (DDAC).

Impact of pH on citric acid antimicrobial activity against Gram-negative bacteria.

The antimicrobial activity of citric acid (CA) is often evaluated without pH adjustment or control and its impact on micro-organisms is better understood in acidic conditions. However, the biocidal action of the fully ionized CA molecule, predominantly available at higher pH, has not been previously investigated. The objective of this study was to evaluate the antimicrobial effect of high (10%) and low (1%) concentrations of CA, each adjusted over a wide range of pH values (4·5, 6·5 and 9·5) relative to the controls exposed to corresponding pH levels alone (no CA).

Formation of stable aggregates by fluid-assembled solid bridges.

When a colloidal suspension is dried, capillary pressure may overwhelm repulsive electrostatic forces, assembling aggregates that are out of thermal equilibrium. This poorly understood process confers cohesive strength to many geological and industrial materials. Here we observe evaporation-driven aggregation of natural and synthesized particulates, probe their stability under rewetting, and measure bonding strength using an atomic force microscope.

Plasmonic Elastic Capsules as Colorimetric Reversible pH-Microsensors.

There is a crucial need for effective and easily dispersible colloidal microsensors able to detect local pH changes before irreversible damages caused by demineralization, corrosion, or biofilms occur. One class of such microsensors is based on molecular dyes encapsulated or dispersed either in polymer matrices or in liquid systems exhibiting different colors upon pH variations. They are efficient but often rely on sophisticated and costly syntheses, and present significant risks of leakage and photobleaching damages, which is detrimental for mainstream applications.

Plasmonic-Based Mechanochromic Microcapsules as Strain Sensors.

Efficiently detecting mechanical deformations within materials is critical in a wide range of devices, from micro-electromechanical systems to larger structures in the aerospace industry. This communication reports the fabrication of new mechanochromic micrometer-size capsules enabling the detection of strains. These microcapsules are synthesized using an emulsification approach.

Preparation and Self-Assembly of Dendronized Janus FeO-Pt and FeO-Au Heterodimers.

Janus nanoparticles (NPs) often referred to as nanosized analogs of molecular surfactants are amphiphilic structures with potential applications in materials science, biomedicine, and catalysis, and their synthesis and self-assembly into complex architectures remain challenging. Here, we demonstrate the preparation of Janus heterodimers via asymmetric functionalization of FeO-Pt and FeO-Au heterodimeric NPs. The hydrophobic and hydrophilic dendritic ligands that carry phosphonic acid and disulfide surface binding groups selectively coat the iron oxide and platinum (or gold) parts of the heterodimer, respectively.

Polycatenar Ligand Control of the Synthesis and Self-Assembly of Colloidal Nanocrystals.

Hydrophobic colloidal nanocrystals are typically synthesized and manipulated with commercially available ligands, and surface functionalization is therefore typically limited to a small number of molecules. Here, we report the use of polycatenar ligands derived from polyalkylbenzoates for the direct synthesis of metallic, chalcogenide, pnictide, and oxide nanocrystals. Polycatenar molecules, branched structures bearing diverging chains in which the terminal substitution pattern, functionality, and binding group can be independently modified, offer a modular platform for the development of ligands with targeted properties.

Quantifying "Softness" of Organic Coatings on Gold Nanoparticles Using Correlated Small-Angle X-ray and Neutron Scattering.

Small-angle X-ray and neutron scattering provide powerful tools to selectively characterize the inorganic and organic components of hybrid nanomaterials. Using hydrophobic gold nanoparticles coated with several commercial and dendritic thiols, the size of the organic layer on the gold particles is shown to increase from 1.2 to 4.

Dendron-Mediated Engineering of Interparticle Separation and Self-Assembly in Dendronized Gold Nanoparticles Superlattices.

Self-assembly of nanoparticles into designed structures with controlled interparticle separations is of crucial importance for the engineering of new materials with tunable functions and for the subsequent bottom-up fabrication of functional devices. In this study, a series of lipophilic, highly flexible, disulfide dendritic wedges (generations 0-4), based on 2,2-bis(hydroxymethyl)propionic acid, was designed to bind Au nanoparticles with a thiolate bond. By controlling the solvent evaporation rate, the corresponding dendron-capped Au hybrids were found to self-organize into hexagonal close-packed (hcp) superlattices.