Reusability of filtering facepiece respirators after decontamination through drying and germicidal UV irradiation

Introduction During pandemics, such as the SARS-CoV-2, filtering facepiece respirators plays an essential role in protecting healthcare personnel. The recycling of respirators is possible in case of critical shortage, but it raises the question of the effectiveness of decontamination as well as the performance of the reused respirators. Method Disposable respirators were subjected to ultraviolet germicidal irradiation (UVGI) treatment at single or successive doses of 60 mJ/cm2 after a short drying cycle (30 min, 70°C). The germicidal efficacy of this treatment was tested by spiking respirators with two staphylococcal bacteriophages (vB_HSa_2002 and P66 phages). The respirator performance was investigated by the following parameters: particle penetration (NaCl aerosol, 10–300 nm), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry and mechanical tensile tests. Results No viable phage particles were recovered from any of the respirators after decontamination (log reduction in virus titre >3), and no reduction in chemical or physical properties (SEM, particle penetrations

Physico-chemical study of the focused electron beam induced deposition process

Tristan Bret

The focused electron beam induced deposition process is a promising technique for nano and micro patterning. Electrons can be focused in sub-angström dimensions, which allows atomic-scale resolution imaging, analysis, and processing techniques. Before the process can be used in controlled applications, the precise nature of the deposition mechanism must be described and modelled. The aim of this research work is to present a physical and chemical description of the focused electron beam induced deposition process. As an introduction, a review of the literature, up to the present day, shows how this process was first identified as the origin of contamination in electron microscopes. Then the modifications made to a scanning electron microscope for deposition experiments are described. Gas supply systems and gas cryo-trapping devices were set up. Electrical and optical systems were constructed for an in-situ monitoring of the process. The experiment procedure was carried out in several phases, with the first being the deposition of flat films of carbon, copper-containing carbon composites, and pure gold for the study of the physics of the process. By measuring the fraction of the probe current that was absorbed in the sample, an accurate description could be made of the propagation of electrons. The backscattered electrons clearly influenced the deposition rate of Cu-containing films. A physical model for scanning deposition was created. The second phase is the deposition of metal-matrix composite tips from a stationary beam. Forward electron scattering was discovered to be responsible for tip formation and shape. A physical model of electron trajectories is included. The third phase is the construction of three-dimensional micro-structures by moving the beam during deposition. The deposited shapes result from an electron range that is larger than the structure size. Further investigation into the chemistry of the process involved the analysis of carbon films by micro-beam techniques. Regardless of the precursor used, the resulting films had a composition as C9H2±xO1±x (x

EPFL2005

Sulfur-bearing lipids for the covalent attachment of supported lipid bilayers to gold surfaces: a detailed characterization and analysis

Jacques Dubochet, Claus Duschl, Martha Liley, Henning Paul-Julius Stahlberg, Horst Vogel, Shaik Mohammed Zakeeruddin

In a recent paper, a new class of synthetic lipids, which self-assemble to form monolayers on gold surfaces, was introduced. The addn. of a monolayer of phospholipids to these layers results in robust supported lipid bilayers designed to reconstitute transmembrane proteins. This paper presents a detailed characterization of the monolayers and bilayers formed by these lipids and assesses their ability for the incorporation of membrane-spanning proteins. Film balance methods, electron microscopy, surface plasmon resonance, Fourier transform IR measurements and Raman spectroscopy show the feasibility of this concept. However, further modifications to improve the thiolipids are necessary. A new strategy for the formation of laterally structured supported lipid bilayers is discussed and initial results are presented. [on SciFinder (R)]

1996

Manipulation of individual carbon nanotubes

Mirko Milas

Carbon nanotubes the long, cylindrical carbon molecules are the most exciting material discovered lately. They offer the possibility for a large number of applications. My task was to explore the way how we can use multi-walled carbon nanotubes (MWNT) in scanning probe applications: Atomic Force Microscopy (AFM) and Scanning Nearfield Optical Microscopy (SNOM). Carbon nanotubes (CNTs) are potentially ideal atomic force microscopy probes because they can have diameters as small as one nanometer, they have robust mechanical properties, and can be specifically functionalized with chemical and biological probes at the tip ends. CNTs will not wear, because they buckle elastically under applied load and thus will stay sharp. They also show exceptional field emission properties, and remarkably enough, the field emission at high currents is accompanied by light emission. This phenomenon offers the possibility to use CNTs as nanometer-size light sources for SNOM. In order to test CNTs for AFM and SNOM applications a mounting method has been elaborated. Two nanomanipulators have been designed and constructed for operations inside a Transmission and Scanning Electron Microscopes (TEM and SEM). This latter one with large work space and available electrical contacts allowed versatile use of nanomanipulator, including in situ field emission, and photon counting measurements using a photodiode. Hundreds of individual MWNT and double-wall nanotubes (DWNT) bundles, produced by arc-discharge (AD) or chemical vapour deposition (CVD) method, have been mounted, one-by-one, on either commercial AFM probes or sharpened metallic wires (W, Au, Pt). The tests show that in both case, AFM and SNOM probes, the weakest point is the attachment of the nanotube to the support. Amorphous carbon deposit is good for attaching nanotubes for limited time and limited applications, but it deforms under the forces that it has been submitted to during AFM scans. This weak bonding of nanotubes is the source of failure in AFM. In field/light emission the high contact resistance, which can change during the mechanical stress exerted by the applied electric field, will lead to a Joule heating of the nanotube/contact area and results a thermal breakdown of the tip. Attempts were made to elaborate a good mechanical and electrical attachment of the carbon nanotubes to the Si/metallic cantilever by using indium as bonding agent.