Protein Film Removal by Means of Low-Pressure Microwave Plasma - An Imaging Ellipsometry Study

Non-equilibrium plasma discharges have been recently proposed to be an effective tool for the removal of proteinaceous residuals from heat-degradable medical instruments. However, the knowledge regarding plasma-protein interactions is still relatively poor, which is a serious drawback for the validation of this technique as well as for its optimisation. This is, among other reasons, caused by the limitations of currently used techniques for monitoring of the rates of protein removal during plasma treatment. The objective of this article is to present an alternative method of evaluation of protein removal, based on imaging ellipsometry, which allows fast and semiquantitative analysis of the treatment efficiency.JRC.I.4-Nanotechnology and Molecular Imagin

Transport Mechanisms in Capillary Condensation of Water at a Single-Asperity Nanoscopic Contact

Transport mechanisms involved in capillary condensation of water menisci in nanoscopic gaps between hydrophilic surfaces are investigated theoretically and experimentally by atomic force microscopy (AFM) measurements of capillary force. The measurements showed an instantaneous formation of a water meniscus by coalescence of the water layers adsorbed on the AFM tip and sample surfaces, followed by a time evolution of meniscus toward a stationary state corresponding to thermodynamic equilibrium. This dynamics of the water meniscus is indicated by time evolution of the meniscus force, which increases with the contact time toward its equilibrium value. Two water transport mechanisms competing in this meniscus dynamics are considered: (1) Knudsen diffusion and condensation of water molecules in the nanoscopic gap and (2) adsorption of water molecules on the surface region around the contact and flow of the surface water toward the meniscus. For the case of very hydrophilic surfaces, the dominant role of surface water transportation on the meniscus dynamics is supported by the results of the AFM measurements of capillary force of water menisci formed at sliding tip–sample contacts. These measurements revealed that fast movement of the contact impedes on the formation of menisci at thermodynamic equilibrium because the flow of the surface water is too slow to reach the moving meniscus

Adhesion and Elasticity in Nanoscale Indentation

The present work proposes an extension of Oliver-Pharr analysis [J. Mater. Res. 7, 1564 (1992)] of unloading force-displacement data obtained in nanoscale indentation experiments to account for contact adhesion. The loading force is considered a sum of the contact elastic and adhesion forces. During the unloading, both forces suffer variations. For conical geometry, the unloading force-displacement curve is described by a sum of a quadratic term (accounting for the elastic force) and a linear term (accounting for adhesive force). Results of atomic force microscopy indentation experiments performed with sharpened silicon tips on poly(dimethylsiloxane) agreed well with the prediction of the proposed theoretical model.JRC.I.4-Nanotechnology and Molecular Imagin

Stochastic Adhesion of Hydroxylated Atomic Force Microscopy Tips to Supported Lipid Bilayers

This work reports results of an atomic force microscopy (AFM) study of adhesion force between hydroxylated AFM tips and supported lipid bilayers (SLBs) of phosphatidylcholine in phosphate buffer saline solution at neutral pH. Silicon nitride AFM probes were hydroxylated by treatment in water vapor plasma and used in force spectroscopy measurements of adhesion force on SLBs with control of contact loading force and residence time. The measurements showed a stochastic behavior of adhesion force that was attributed to stochastic formation of hydrogen bonds between the hydroxyl groups on the AFM tip and oxygen atoms from the phosphate groups of the phosphatidylcholine molecules. Analysis of a large number of force curves revealed a very low probability of hydrogen bond formation, a probability that increased with the increase of contact loading force and residence time. The variance and mean values of adhesion force showed a linear dependence on each other, which indicated that hydrogen bond formation obeyed the Poisson distribution of probability. This allowed for the quantitative determination of the rupture force per hydrogen bond of about 40 pN and showed the absence of other nonspecific interaction forces

Atomic Force Microscopy Indentation of Fluorocarbon Thin Films Fabricated by Plasma Enhanced Chemical Deposition at Low Radio Frequency Power

Atomic force microscopy (AFM) indentation technique is used for characterization of mechanical properties of fluorocarbon (CFx) thin films obtained from C4F8 gas by plasma enhanced chemical vapour deposition at low r.f. power (5¿30 W) and d.c. bias potential (10¿80 V). This particular deposition method renders films with good hydrophobic property and high plastic compliance. Commercially available AFMprobeswith stiff cantilevers (10¿ 20 N/m) and silicon sharpened tips (tip radius b10 nm) are used for indentations and imaging of the resulted indentation imprints. Force depth curves and imprint characteristics are used for determination of film hardness, elasticity modulus and plasticity index. Themeasurements showthat the decrease of the discharge power results in deposition of films with decreased hardness and stiffness and increased plasticity index. Nanolithography based on AFM indentation is demonstrated on thin films (thickness of 40 nm) with good plastic compliance.JRC.DDG.I.5-Nanobioscience

Cleaning and Hydrophilization of Atomic Force Microscopy Silicon Probes

The silicon surface of commercial atomic force microscopy (AFM) probes loses its hydrophilicity by adsorption of airborne or package-released hydrophobic contaminants. Cleaning of the probes by acid piranha solution or discharge plasma removes the contaminants and renders very hydrophilic probe surfaces. Time-of-flight secondary-ion mass spectroscopy and X-ray photoelectron spectroscopy investigations showed that the native silicon oxide films on the AFM probe surfaces are completely covered by contaminants for the as-received AFM probes, while the cleaning methods effectively remove much of the hydrocarbons to reveal the underlying oxidized silicon of the probes. Cleaning procedure drastically affect the results of adhesive force measurements in water and air. Thus, significant adhesive force values arise in deionized water due to the formation of a bridge of hydrophobic material at the AFM tip-sample contact. Cleaning of the AFM tip and sample surfaces results in a significant increase of the adhesive force in air. Presence of water soluble contaminants at the tip-sample contact lower the capillary pressure in the water bridge formed by capillary condensation at the AFM tip-sample contact, and this results in a smaller adhesive force between the contaminated surfaces of the AFM tip and sample.JRC.I.4-Nanotechnology and Molecular Imagin

Probing Elasticity and Adhesion of Live Cells by Atomic Force Microscopy Indentation

Atomic force microscopy (AFM) indentation has become an important technique for quantifying the mechanical properties of live cells at nanoscale. However, determination of cell elasticity modulus from the force- displacement curves measured in the AFM indentations is not a trivial task. The present work shows that these force- displacement curves are affected by indenter-cell adhesion force, while the use of an appropriate indentation model may provide information on the cell elasticity and the work of adhesion of the cell membrane to the surface of the AFM probes. A recently proposed indentation model (Sirghi, Rossi in Appl Phys Lett 89:243118, 2006), which accounts for the effect of the adhesion force in nanoscale indentation, is applied to the AFM indentation experiments performed on live cells with pyramidal indenters. The model considers that the indentation force equilibrates the elastic force of the cell cytoskeleton and the adhesion force of the cell membrane. It is assumed that the indenter-cell contact area and the adhesion force decrease continuously during the unloading part of the indentation (peeling model). Force-displacement curves measured in indentation experiments performed with silicon nitride AFM probes with pyramidal tips on live cells (mouse fibroblast Balb/c3T3 clone A31-1-1) in physiological medium at 37°C agree well with the theoretical prediction and are used to determine the cell elasticity modulus and indentercell work of adhesion.JRC.I.4-Nanobioscience

Use of a Low-Pressure Plasma Discharge for the Decontamination and Sterilization of Medical Devices

Nonequilibrium low-pressure plasma discharges are extensively studied for their applications in the field of decontamination and sterilization of medical devices. The aim of this contribution is to discuss and demonstrate feasibility of oxygen low-pressure inductively coupled plasma (ICP) discharges for removal of various kinds of biological contamination. We demonstrate the ability of ICP discharges for the sterilization of bacterial spores and the removal of biological contamination from proteins and pyrogens.JRC.I.4-Nanobioscience

High visible light photocatalytic activity of nitrogen-doped ZnO thin films deposited by HiPIMS

International audienceReactive High Power Impulse Magnetron Sputtering (HiPIMS) of a pure Zn target in Ar/N$_2$/O$_2$ gas mixture was used to synthesize ZnO$_x$N$_y$ thin films with nitrogen content and optical band-gap energy values ranging over 0–6.2 at.% and 3.34–1.67 eV, respectively. The fine control of the nitrogen content in the deposited ZnO$_x$N$_y$ thin films composition was possible through the stabilization of the reactive HiPIMS discharge in the transition region, between the metallic and compound target sputtering modes. Various analytical techniques such as AFM, XPS, XRD, UV–Vis and Raman spectroscopy have been employed to characterize the properties of the deposited thin films. The photocatalytic activity, light excitation efficiency and life time of photo-generated charge carriers in the ZnO$_x$N$_y$ films were investigated by photo-electrochemical and photo-current measurements during visible light on/off irradiation cycles. The as-deposited films showed poor visible-light photocatalytic activity and photo-current response. Post-deposition annealing of the films in nitrogen atmosphere resulted in a slight enhancement of crystalline order. However, the thermal treatment improved considerably the film photocatalytic activity and stability for water splitting under visible light irradiation. The optimum photo-current response and photocata-lytic activity have been obtained for the annealed ZnO$_x$N$_y$ films with a nitrogen content of 3.4 at.% (photon-to-current efficiency up to 33% at λ = 370 nm and 0.5 V biasing potential vs. Ag/AgCl). Increasing the nitrogen content above this value, in spite of lowering the energy band-gap, worsened the visible light photocatalytic activity of the films due to deterioration of the crystalline order