Non-Invasive Vibrational SFG Spectroscopy Reveals That Bacterial Adhesion Can Alter the Conformation of Grafted “Brush” Chains on SAM

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.

Stabilization of Insulin by Adsorption on a Hydrophobic Silane Self-Assembled Monolayer

“…If the change was purely due to a hydrophobic effect, then the increase in the asymmetric/symmetric peak ratio to 1.58 would correspond to a 5° increase in the tilt angle of the methyl group. This is comparable to other hydrophobic interactions measured by SFS, for example, the 3.3° increase of the CH 3 tilt angle of octadecanethiol on Au(111) when the solvent was changed from distilled water to a hydrophobic bacterium 48 . However, the appearance of aromatic C-H peaks from phenylalanine and tyrosine side-chains clearly shows that insulin adsorbs in an ordered fashion on the hydrophobic surface, and that a pure hydrophobic effect is unlikely to 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 be the sole cause of the observed change.…”

In vitro observation of dynamic ordering processes in the extracellular matrix of living, adherent cells

“…81 Similar results were reported by Bulard et al using bacteria. 82 As adherent cells also do not modify SFG spectra, 80 it can be concluded that ordered intracellular structures (including membranes) do not contribute significantly to SFG signals in this measurement setup.…”

Non-invasive SFG spectroscopy: a tool to reveal the conformational change of grafted chains due to bacterial adhesion

“…Moreover, modelling the experimental SFG spectra reveals a measurable change of the SAM conformation depending on the hydrophobic-hydrophilic character of the environment. These results show that bacteria are able to modify their support at the molecular level 17 . Therefore, this result should be taken into account for the design of new biomaterials.…”

“…As described previously 15 , we obtained in these conditions an ODT SAM film thickness of ~2 nm. Surface topography of these substrates was characterized by Atomic Force Microscopy (AFM) in contact mode 17 . The gold surface topography presents plantens of 1-2 µm 2 delimitated by grooves of 20-30 nm depth.…”

“…We have analyzed it in details 17 and extracted the two molecular conformations involved in the SAM. The spectrum consists mainly of the three strong bands of the methyl group: the methyl symmetric stretch band at 2875 cm -1 , the Fermi resonance of the CH 3 symmetric mode with two quantas of the CH 3 bending mode at 2936 cm -1 and the methyl asymmetric stretch band at 2964 cm -1 .…”