Adhesion of Pseudomonas fluorescens (ATCC 17552) to Nonpolarized and Polarized Thin Films of Gold (original) (raw)
Related papers
Polarization at metal-biomolecular interfaces in solution
Journal of The Royal Society Interface, 2010
Metal surfaces in contact with water, surfactants and biopolymers experience attractive polarization owing to induced charges. This fundamental physical interaction complements stronger epitaxial and covalent surface interactions and remains difficult to measure experimentally. We present a first step to quantify polarization on even gold (Au) surfaces in contact with water and with aqueous solutions of peptides of different charge state (A3 and Flg-Na3) by molecular dynamics simulation in all-atomic resolution and a posteriori computation of the image potential. Attractive polarization scales with the magnitude of atomic charges and with the length of multi-poles in the aqueous phase such as the distance between cationic and anionic groups. The polarization energy per surface area is similar on aqueous Au f1 1 1g and Au f1 0 0g interfaces of approximately 250 mJ m 22 and decreases to 270 mJ m 22 in the presence of charged peptides. In molecular terms, the polarization energy corresponds to 22.3 and 20.1 kJ mol 21 for water in the first and second molecular layers on the metal surface, and to between 240 and 0 kJ mol 21 for individual amino acids in the peptides depending on the charge state, multi-pole length and proximity to the surface. The net contribution of polarization to peptide adsorption on the metal surface is determined by the balance between polarization by the peptide and loss of polarization by replaced surface-bound water. On metal surfaces with significant epitaxial attraction of peptides such as Au f1 1 1g, polarization contributes only 10-20% to total adsorption related to similar polarity of water and of amino acids. On metal surfaces with weak epitaxial attraction of peptides such as Au f1 0 0g, polarization is a major contribution to adsorption, especially for charged peptides (280 kJ mol 21 for peptide Flg-Na 3 ). A remaining water interlayer between the metal surface and the peptide then reduces losses in polarization energy by replaced surface-bound water. Computed polarization energies are sensitive to the precise location of the image plane (within tenths of Angstroms near the jellium edge). The computational method can be extended to complex nanometre and micrometer-size surface topologies.
DLVO and steric contributions to bacterial deposition in media of different ionic strengths
Colloids and Surfaces B: Biointerfaces, 1999
The deposition of eight bacterial strains on Teflon and glass in aqueous media with ionic strengths varying between 0.0001 and 1 M was measured and interpreted. Two types of interactions were considered: (1) those described by the DLVO theory, which comprise van der Waals attraction and electrostatic repulsion (bacteria and surfaces are both negatively charged); and (2) steric interactions between the outer cell surface macromolecules and the substrata. As a trend, at low ionic strength (B0.001 M), deposition is inhibited by DLVO-type electrostatic repulsion, but at high ionic strength (]0.1 M) it is dominated by steric interactions. The ionic strength at which the transition from the DLVO-controlled to the sterically controlled deposition occurs, is determined by the extension of the macromolecules into the surrounding medium, which varied between 5 and 100 nm among the bacterial strains studied. The steric interactions either promote deposition by bridging or inhibit it by steric repulsion. Between Teflon and hydrophobic bacteria, bridging is generally observed. The surface of one bacterial strain contains amphiphilic macromolecules that form bridges with Teflon but induce steric repulsion on glass. The presence of highly polar anionic polysaccharide coatings on the cell impedes attachment on both glass and Teflon. For practice, the general conclusion is that the deposition of most bacteria is: (1) strongly inhibited by DLVO-type electrostatic repulsion in aqueous environments of low ionic strength such as rain water, streams and lakes; (2) controlled by DLVO and/or steric interactions in systems as domestic waste waters and saliva; and (3) determined by steric interactions only in more saline environments as milk, urine, blood and sea water.
Analytical insights on ion behaviour at interfaces
Journal of Electroanalytical Chemistry, 2011
We report new analytical results for the behaviour of the free energy of an ion between two media that are characterized by different dielectric permitivities including the ion polarizability as a phenomenological parameter. The differences in the free energy induced by the new terms related to the polarizability are on the order of a few k B T ($25 meV), k B being the Boltzmann constant and T the temperature of the system not far from the room temperature, and may explain the enhanced propensity of halogen anions for the water-air or water-lipid interfaces with increasing ionic polarizability.
Nature Communications, 2018
Metallic nanostructures have become popular for applications in therapeutics, catalysts, imaging, and gene delivery. Molecular dynamics simulations are gaining influence to predict nanostructure assembly and performance; however, instantaneous polarization effects due to induced charges in the free electron gas are not routinely included. Here we present a simple, compatible, and accurate polarizable potential for gold that consists of a Lennard–Jones potential and a harmonically coupled core-shell charge pair for every metal atom. The model reproduces the classical image potential of adsorbed ions as well as surface, bulk, and aqueous interfacial properties in excellent agreement with experiment. Induced charges affect the adsorption of ions onto gold surfaces in the gas phase at a strength similar to chemical bonds while ions and charged peptides in solution are influenced at a strength similar to intermolecular bonds. The proposed model can be applied to complex gold interfaces, ...
Probing Bacterial Electrosteric Interactions Using Atomic Force Microscopy
Environmental Science & Technology, 2000
Atomic force microscopy (AFM) was used to probe the effects of pH, ionic strength, and the presence of bacterial surface polymers on interaction forces between individual, negatively charged bacteria and silicon nitride. Bacterial surface polymers dominated interactions between bacteria and AFM silicon nitride tips. The measured forces were represented well by an electrosteric repulsion model accounting for repulsion between the tip and bacterial polymers but were much larger in magnitude and extended over longer distances (100's of nanometers) than predicted by DLVO theory. The equilibrium length (L o ) of the polymers was allowed to vary with solution chemistry to account for intramolecular electrostatic interactions between individual polymer units. The effects of the variables pH and ionic strength on bacterial interaction forces were investigated independently. Pseudomonas putida KT2442 was studied in 1 mM MOPS buffer at pH values of 2.2, 4.75, 7.00, and 8.67. Burkholderia cepacia G4 was studied in 1 mM MOPS buffer at pH values of 2.2, 4.75, and 6.87. Then, the pH was held constant at 4.5 or 4.75, and the ionic strength was studied in 0.01, 1, or 100 mM MOPS buffer (for each microbe). For KT2442 (in 1 mM MOPS buffer), L o increased from 230 to 750 nm as pH increased from 4.75 to 8.67. For G4 (in 1 mM MOPS buffer), L o increased from 350 nm at pH 2.2 to 1040 nm at pH 7.0. Varying the ionic strength between 0.01 and 100 mM did not affect the equilibrium length of the polymers nearly as much as pH. Partially removing polysaccharides from the bacterial surfaces resulted in lower repulsive forces that decayed much more rapidly. The magnitude of the measured forces in these experiments and the equilibrium lengths predicted by the electrosteric model are comparable to other force measurements and size estimates on polymers and polysaccharides.
Journal of Colloid and Interface Science, 1987
Direct measurements of interactions between one negatively charged mica surface and one positively charged modified mica surface immersed in electrolyte solutions are reported. The modified mica surface was obtained by Langmuir-Blodgett deposition of dimethyldioctadecylammonium ions which made the surface hydrophobic and gave it a small positive charge. The interactions between these dissimilar surfaces are dominated by attractive double-layer forces. However, in concentrated electrolyte solutions (C > 10 -2 M) and/or at short surface separations (D < 20 nm) the measured attraction is stronger than that expected from conventional DLVO theory. This is suggested to be due to either a breakdown of the Poisson-Boltzmann approximation or the presence of an additional force related to the attractive force previously observed between two hydrophobic surfaces in aqueous solutions.
Antibacterial properties of metal and PDMS surfaces under weak electric fields
Surface & Coatings Technology, 2020
The adhesion of several species of bacteria on two parallel rectangular electrodes under weak electric fields was studied. The electrodes were based on native metal or PDMS coated Cu. After 2 hours of contact at a voltage of 0.2 to 1V without any current, the Zn cathode showed a bacterial repellent effect with a difference in bacterial adhesion of about 1.5 to 2 log CFU/cm2 on the anode. Al electrodes were inactive due to their passivation by the alumina layer. At 1V, both Zn and Al exhibited more than 80% mortality of suspended bacteria. The Cu electrodes showed a very high bactericidal effect even at 0V, and the bacterial adhesion on its surface was too weak to see a difference between the two electrodes. A similar study carried out on PDMS surfaces, covering Cu electrodes, revealed that a difference of 1 log CFU/cm2 of bacterial adhesion between the cathode and anode surfaces can be obtained by applying a voltage ranging from 10 to 30V. This cathodic repellent effect was specific to staphylococcus species, suggesting that in the presence of a PDMS coating, the electrostatic forces on the surface are too low to be the main factor governing bacterial adhesion.
Non-covalent interactions at electrochemical interfaces: one model fits all?
The shift with increasing concentration of alkali-metal cations of the potentials of both the spike and the hump observed in the cyclic voltammograms of Pt(111) electrodes in sulfuric acid solutions is shown to obey the simple model recently developed by us to explain the effect of non-covalent interactions at the electrical double layer. The results suggest that the model, originally developed to describe the effect of alkali-metal cations on the cyclic voltammogram of cyanide-modified Pt(111) electrodes, is of general applicability and can explain quantitatively the effect of cations on the properties of the electrical double layer.
Specific Ion Effects: Why DLVO Theory Fails for Biology and Colloid Systems
Physical Review Letters, 2001
This year marks the 65 th birthday of our Founding Professor, Barry Ninham. As a result, Barry formally retired at the end of the year. His retirement is a formal one only, and the Department hopes that he will be with us for many years yet. Such occasions demand politeness, a nicety that makes it difficult to express the genuine depth of gratitude we owe Barry for so many years of dedication and belief in the department that he built. His sheer energy has forged a world-beating group over three decades. His style has indelibly marked the Department: we remain an informal, inquiring inter-disciplinary group, interested above all in the scientific questions that lie between the traditional disciplines. Barry remains active on many fronts; research continues here and in Europe. In addition, his commitments to UNESCO continue, where he is setting up an international network of institutes to study all aspects of water resources, a looming problem in many parts of the globe. The ANU will host one of those nodes; others are being set up in Scandinavia and elsewhere. Another of our most senior members, Professor Stjepan Marcelja has been appointed Director of the Rudjer Boskovic Institute in Zagreb. The appointment, leading an institution with over four hundred scientists, testifies to the highest international status of our group. We congratulate him, and hope to see him return to science here as often as possible.