Published: March 16, 2011 r2011 American Chemical Society 4928 dx.doi.org/10.1021/la200205e | Langmuir 2011, 27, 4928–4935 ARTICLE pubs.acs.org/Langmuir Non-Invasive Vibrational SFG Spectroscopy Reveals That Bacterial Adhesion Can Alter the Conformation of Grafted “Brush” Chains on SAM Emilie Bulard,* ,† Ziang Guo, † Wanquan Zheng, † Henri Dubost, † Marie-Pierre Fontaine-Aupart, † Marie-No € elle Bellon-Fontaine, ‡ Jean-Marie Herry, ‡ Romain Briandet, ‡ and Bernard Bourguignon † † Institut des Sciences Mol  eculaires d’Orsay, ISMOCNRS, Universit  e Paris Sud, B^ at. 350 91405 Orsay cedex, France ‡ INRA AgroParisTech, UMR 1319 Micalis, 91300 Massy, France 1. INTRODUCTION All solidliquid interfaces are potentially subject to bacterial adhesion and biofilm formation. When they concern pathogens, these microbial consortia are involved in nosocomial and food born infections. 1,2 Thus, the control of bacterial adhesion to abiotic surfaces remains a current challenge for the design of new materials with improved properties such as functional or brush coatings to prevent and control surface biocontamination 3 but also to control biofilms eradication. Bacterial adhesion on an inert surface is largely governed, as for any colloidal particles, by non-covalent molecular interactions (coulombian, van der Waals, Lewis acidbase). These interactions depend on the nature of the bacteria cell envelopes (peptidoglycan, exoproteins, exopolysaccharides, pili, flagela, and so forth) and on the physicochemical properties of the surfaces. 4,5 Their macroscopic and microscopic analyses have been largely developed (topography and roughness, hydrophobic/hydrophilic character, acid/base properties, surface potential, and so forth) in order to propose predictive models for bacteria adhesion. 68 However, divergences between these models and experimental results have been reported particularly in the case of surfaces functionalized with physisorbed or grafted chains. 911 So the question arises whether bacterial adhesion modi fies the conformation and the physicochemical properties of these grafted chains or not. To answer this question, it is necessary to use a biophysical technique able to provide information on interactions at the molecular level with selectivity for the solid-bacteria interface under in situ conditions (e.g., in aqueous environment in order to preserve cell viability). SFG vibrational spectroscopy has recently been applied to biomolecular systems. 1214 Its high surface specificity and sensitivity has allowed us to understand interactions at the molecular level between an organized molecular system and a substrate. SFG is also emerging as a tool more adapted than infrared and Raman spectroscopy to study the molecular conformation of SAMs. 15 The method was used here for the first time to investigate the reactivity of a hydrophobic model surface (ODT SAM) to the adhesion of a single layer of ovococcoid hydrophilic and hydro- phobic model bacterial strains suspended in aqueous solution. SAMs are well suited for such SFG experiments due not only to their high molecular order 16 but also to their stability in air and in contact with aqueous surfaces. They are also considered in view of potential application as coatings able to resist bacterial contamina- tion. This work reveals that both water and bacteria interact with the ODT layer and modify its conformation. The hydrophobic cells tend to flatten the SAM terminal groups while the hydrophilic ones have a brush effect stronger than that of an aqueous solution. 2. EXPERIMENTAL SECTION 2.1. Materials. Substrates consisted of borosilicate glass coated with a polycrystalline gold film of 250-nm thickness and annealed in an oven at 600 °C over 30 s. A self-assembled monolayer of octadecanethiol was Received: January 17, 2011 Revised: February 15, 2011 ABSTRACT: Understanding bacterial adhesion on a surface is a crucial step to design new materials with improved properties or to control biofilm formation and eradication. Sum Frequency Generation (SFG) vibrational spectroscopy has been employed to study in situ the conformational response of a self-assembled monolayer (SAM) of octadecanethiol (ODT) on a gold film to the adhesion of hydrophilic and hydrophobic ovococcoid model bacteria. The present work highlights vibrational SFG spectroscopy as a powerful and unique non-invasive biophysical technique to probe and control bacteria interaction with ordered surfaces. Indeed, the SFG vibrational spectral changes reveal different ODT SAM conformations in air and upon exposure to aqueous solution or bacterial adhesion. Furthermore, this effect depends on the bacterial cell surface properties. The SFG spectral modeling demonstrates that hydrophobic bacteria flatten the ODT SAM alkyl chain terminal part, whereas the hydrophilic ones raise this ODT SAM terminal part. Microorganism-induced alteration of grafted chains can thus affect the desired interfacial functionality, a result that should be considered for the design of new reactive materials.