Antibacterial activity of silver nanoparticles: A surface science insight

Silver nanoparticles constitute a very promising approach for the development of new antimicrobial systems. Nanoparticulate objects can bring significant improvements in the antibacterial activity of this element, through specific effect such as an adsorption at bacterial surfaces. However, the mechanism of action is essentially driven by the oxidative dissolution of the nanoparticles, as indicated by recent direct observations. The rote of Ag+ release in the action mechanism was also indirectly observed in numerous studies, and explains the sensitivity of the antimicrobial activity to the presence of some chemical species, notably halides and sulfides which form insoluble salts with Ag+. As such, surface properties of Ag nanoparticles have a crucial impact on their potency, as they influence both physical (aggregation, affinity for bacterial membrane, etc.) and chemical (dissolution, passivation, etc.) phenomena. Here, we review the main parameters that will affect the surface state of Ag NPs and their influence on antimicrobial efficacy. We also provide an analysis of several works on Ag NPs activity, observed through the scope of an oxidative Ag+ release. (C) 2015 Elsevier Ltd. All rights reserved

Host-guest chemistry with water-soluble gold nanoparticle supraspheres

The uptake of molecular guests, a hallmark of the supramolecular chemistry of cages and containers, has yet to be documented for soluble assemblies of metal nanoparticles. Here we demonstrate that gold nanoparticle-based supraspheres serve as a host for the hydrophobic uptake, transport and subsequent release of over two million organic guests, exceeding by five orders of magnitude the capacities of individual supramolecular cages or containers and rivalling those of zeolites and metal-organic frameworks on a mass-per-volume basis. The supraspheres are prepared in water by adding hexanethiol to polyoxometalate-protected 4 nm gold nanoparticles. Each 200 nm assembly contains hydrophobic cavities between the estimated 27,400 gold building blocks that are connected to one another by nanometre-sized pores. This gives a percolated network that effectively absorbs large numbers of molecules from water, including 600,000, 2,100,000 and 2,600,000 molecules (35, 190 and 234 g l(-1)) of para-dichorobenzene, bisphenol A and trinitrotoluene, respectively

Elaboration de biopiles à combustible incorporant des micro-organismes par procédé sol-gel

Cette thèse porte sur l encapsulation de cellules vivantes (bactéries et micro-algues) dans des gels de silice obtenus grâce au procédé sol-gel, en vue de la réalisation de biopiles à combustible. Ces matrices sont synthétisées par une méthode de chimie douce en voie aqueuse, afin de permettre la survie des micro-organismes. Comme la silice est un matériau isolant électrique, il est nécessaire de coupler celle-ci avec un matériau conducteur. Deux approches ont été suivies : la première consiste à utiliser du feutre de carbone comme électrode, et à intégrer le gel et les cellules dans la porosité de celui-ci. La seconde consiste à incorporer des nanotubes de carbone lors de la formation du gel, afin que ceux-ci forment un réseau conducteur d électrons. Un moyen simple d imprégner l intérieur d un feutre hydrophobe par des phases aqueuses a été développé. Le transport de matière par diffusion à l intérieur de ces feutres gélifiés a ensuite été étudié. Nous avons ensuite caractérisé l activité électrochimique de cellules vivantes à l intérieur du feutre. La présence de glucose permet la production de métabolites électroactifs par les bactéries. Ces métabolites peuvent être utilisés pour alimenter une pile à combustible. Nous avons alors développé une biopile qui intègre ces micro-organismes. Cette biopile génère une puissance surfacique de 40 mW/m2 d électrode. Le système intégrant des nanotubes de carbone a été caractérisé par spectroscopie d impédance. Cette technique nous a permis de mettre en évidence la coexistence de deux modes de conduction, assurés par les ions dans la porosité de la silice, ou bien par les électrons dans le réseau de nanotubes. Ce réseau est susceptible de se réorganiser au cours du temps, et sa conductivité augmente alors. La survie des cellules a été confirmée dans ces matrices, ce qui pourrait conduire à la conception de systèmes innovants couplant électrochimie et biologie (biopiles, capteurs, etc.).This thesis deals with the encapsulation of living cells (bacteria and micro-algae) in silica gels, obtained through the sol-gel process, in order to build bio-fuel cells. The silica matrices are prepared following a soft chemistry method, in aqueous media, to ensure the viability of the micro-organisms. Since silica is an insulating material, it has to be associated to an electrical conductor. Two approaches have been followed: the first one consists in using graphite felt as an electrode material, while its porosity is filled with the silica gel and cells. The second approach consists in the incorporation of carbon nanotubes during the synthesis of the silica matrix. The nanotubes form a conductive network once the gel is formed. A method has been developed to make the surface of the graphite felt more hydrophilic. Thus water-based chemistry can be performed in its porosity. Mass transport within the gelified felt has been studied. We have then characterized the electrochemical activity of the living cells inside the felt. In presence of glucose, we could observe the production of electroactive metabolites. These could be used as a fuel to power the fuel cell. This device produced a surface power of 40 mW/m2 (electrode footprint). The system that contained carbon nanotubes was characterized principally by using impedance spectroscopy. With this technique, we were able to observe the coexistence of two modes of conductions. The electrical current is related to both the migration of the ions in the mesoporosity of the gel and to the circulation of the electrons in the nanotube network. This network could evolve inside of the mesoporous silica gel, leading to an increase of its conductivity. Survival of bacteria was confirmed in presence of the carbon nanotubes and inside these matricesPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Mass Transport Properties of Silicified Graphite Felt Electrodes

International audienceMass transport properties of electrodes prepared from graphite felt, as such and after silicification, have been studied using cyclic voltammetry. Within the graphite felt, the mass transport of a probe changes with decreasing scan rate, from a radial diffusion around fibers to a regime that is analogous to “thin-layer” systems. Furthermore, unlike classical “thin-layer” systems, the volume comprised in the felt is macroscopic (resulting in high current densities), while the time required to consume all diffusive species remains in the 1 min range. Silicification of graphite felt does not impact on the mass transport of the negatively charged molecular probe Fe(CN)63– but significantly slows mass transport of positively charged Ru(NH3)63+. In the latter case, a parallel decrease of peak current intensity reflects limited mobility of the probe due to its strong interaction with the surface of the pore walls. These data provide important information for the optimization of the working conditions of these electrodes for the design of biosensors and biofuel cells

Silica-carbon hydrogels as cytocompatible bioelectrodes

International audienceBioelectrodes were prepared by encapsulating bacteria in a silica hydrogel, in the pores of graphite felt, which acts as a conductive network in the material. We observed the conversion of glucose into metabolites that could diffuse into the mesopores of the silica network and be oxidised at the graphite surface

Evaluation of Hydrophilized Graphite Felt for Electrochemical Heavy Metals Detection (Pb2+, Hg2+)

Hydrophilized graphite felt has been used, for the first time, for the electrochemical detection of Hg2+ ions both as single metal species and via its simultaneous detection with Pb2+. To do so, square wave voltammetry (SWV) method was developed with alginate modified graphite felt as working electrode. The structure of the graphite felt such as its high porosity and specific surface area coupled with its good electrical conductivity allows achieving large peak currents via the SWV method, suggesting that the alginate coating helps to preconcentrate metals at the carbon surface. The as-described electrode has low cost, it is easy to manipulate, and the electrochemical analysis can be performed by simple immersion of the felt in the metal solution

Opening of an Accessible Microporosity in an Otherwise Nonporous Metal–Organic Framework by Polymeric Guests

The development of highly porous metal–organic frameworks (MOFs) is greatly sought after, due to their wide range of applications. As an alternative to the development of new structures, we propose to obtain new stable configurations for flexible MOFs by insertion of polymeric guests. The guests prevent the otherwise spontaneous closing of the host frameworks and result in stable opened forms. Introduced at a fraction of the maximal capacity, polymer chains cause an opening of the occupied nanochannels, and because of the MOF reticular stiffness, this opening is propagated to the neighboring nanochannels that become accessible for adsorption. Composites were obtained by in situ polymerization of vinyl monomers in the nanochannels of an otherwise nonporous MOF, resulting in homogeneously loaded materials with a significant increase of porosity (<i>S</i>_BET = 920 m²/g). In addition, by limiting the accessible configurations for the framework and forbidding the formation of a reactive intermediate, the polymeric guest prevented the thermal degradation of the host MOF even at very low loading (as low as 3 wt %) and increased its stability domain by more than 200 °C

Mass Transport Properties of Silicified Graphite Felt Electrodes

Mass transport properties of electrodes prepared from graphite felt, as such and after silicification, have been studied using cyclic voltammetry. Within the graphite felt, the mass transport of a probe changes with decreasing scan rate, from a radial diffusion around fibers to a regime that is analogous to “thin-layer” systems. Furthermore, unlike classical “thin-layer” systems, the volume comprised in the felt is macroscopic (resulting in high current densities), while the time required to consume all diffusive species remains in the 1 min range. Silicification of graphite felt does not impact on the mass transport of the negatively charged molecular probe Fe­(CN)₆^3– but significantly slows mass transport of positively charged Ru­(NH₃)₆³⁺. In the latter case, a parallel decrease of peak current intensity reflects limited mobility of the probe due to its strong interaction with the surface of the pore walls. These data provide important information for the optimization of the working conditions of these electrodes for the design of biosensors and biofuel cells