Abstract
Surface colonization by microorganisms leads to the formation of biofilms, i.e. aggregates of bacteria embedded within a matrix of extracellular polymeric substance. This promotes adhesion to the surface and protects bacterial community, providing an antimicrobial-resistant environment. The inhibition of biofilm growth is a crucial issue for preventing bacterial infections. Inorganic nanoparticle/Teflon-like (CFx) composites deposited via ion beam sputtering demonstrated very efficient antimicrobial activity. In this study, we developed Ag-CFx thin films with tuneable metal loadings and exceptional in-plane morphological and chemical homogeneity. Ag-CFx antimicrobial activity was studied via mid-infrared attenuated total reflection spectroscopy utilizing specifically adapted multi-reflection waveguides. Biofilm was sampled by carefully depositing the Ag-CFx film on IR inactive regions of the waveguide. Real-time infrared spectroscopy was used to monitor Pseudomonas fluorescens biofilm growth inhibition induced by the bioactive silver ions released from the nanoantimicrobial coating. Few hours of Ag-CFx action were sufficient to affect significantly biofilm growth. These findings were corroborated by atomic force microscopy (AFM) studies on living bacteria exposed to the same nanoantimicrobial. Morphological analyses showed a severe bacterial stress, leading to membrane leakage/collapse or to extended cell lysis as a function of incubation time.
Highlights
Silver nanoparticles (AgNPs) are the most widespread used inorganic nanoantimicrobial agent[1], and are already extensively used in health industry, for food storage, in manufacturing industry, and numerous environmental applications[2]
Antibacterial Ag nanophases were proven to be free of potentially toxic inorganic fluorides, which is counterintuitive and different from what was found in homologous systems[14], supporting the utility of sputter-deposited Ag-CFx materials for real-life applications[30]
Antimicrobial ion release kinetics were studied by electro-thermal atomic absorption spectroscopy (ETAAS), while transmission electron microscopy (TEM) was employed to rule out that entire AgNPs were released, which may represent atoxicological risk
Summary
Silver nanoparticles (AgNPs) are the most widespread used inorganic nanoantimicrobial agent[1], and are already extensively used in health industry, for food storage, in manufacturing industry, and numerous environmental applications[2]. Antibacterial Ag nanophases were proven to be free of potentially toxic inorganic fluorides, which is counterintuitive and different from what was found in homologous systems[14], supporting the utility of sputter-deposited Ag-CFx materials for real-life applications[30]. These materials provide the advantageous characteristics of the fluoropolymer matrix, i.e. anti-stain, anti-fouling, and water repellent; due to the presence of AgNPs, they can exert a strong and wide antimicrobial activity and –in case of high metal loading– an additional antistatic function. The combined spectroscopic/morphological approach presented for the study of nanomaterial-biofilm interactions has great prospective importance, since it can decouple ion-mediated effects from nanoparticle-mediated and direct contact ones, contributing to separately elucidate bioactivity mechanisms such as those based on ionic release
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