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

Bio-nanotechnology application in wastewater treatment

The nanoparticles have received high interest in the field of medicine and water purification, however, the nanomaterials produced by chemical and physical methods are considered hazardous, expensive, and leave behind harmful substances to the environment. This chapter aimed to focus on green-synthesized nanoparticles and their medical applications. Moreover, the chapter highlighted the applicability of the metallic nanoparticles (MNPs) in the inactivation of microbial cells due to their high surface and small particle size. Modifying nanomaterials produced by green-methods is safe, inexpensive, and easy. Therefore, the control and modification of nanoparticles and their properties were also discussed

The antibacterial activity of polyoxometalates: structures, antibiotic effects and future perspectives

Polyoxometalates (POMs) are, mostly anionic, metal oxide compounds that span a wide range of tunable physical and chemical features rendering them very interesting for biological purposes, an continuously emerging but little explored field. Due to their biological and biochemical effects, including antitumor, -viral and -bacterial properties, POMs and POM-based systems are considered as promising future metallodrugs. In this article, we focus on the antibacterial activity of POMs and their therapeutic potential in the battle against bacteria and their increasing resistance against pharmaceuticals. Recent advances in the synthesis of POMs are highlighted, with emphasis on the development and properties of biologically active POM-based hybrid and nanocomposite structures. By analysing the antibacterial activity and structure of POMs, putative mode of actions are provided, including potential targets for POM–protein interactions, and a structure–activity-relationship was established for a series of POMs against two bacteria, namely Helicobacter pylori and Streptococcus pneumoniae.info:eu-repo/semantics/publishedVersio

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