Cell spreading on quartz crystal microbalance elicits positive frequency shifts indicative of viscosity changes

Cell attachment and spreading on solid surfaces was investigated with a home-made quartz crystal microbalance (QCM), which measures the frequency, the transient decay time constant and the maximal oscillation amplitude. Initial interactions of the adsorbing cells with the QCM mainly induced a decrease of the frequency, coincident with mass adsorption. After about 80min, the frequency increased continuously and after several hours exceeded the initial frequency measured before cell adsorption. Phase contrast and fluorescence microscopy indicated that the cells were firmly attached to the quartz surface during the frequency increase. The measurements of the maximal oscillation amplitude and the transient decay time constant revealed changes of viscoelastic properties at the QCM surface. An important fraction of these changes was likely due to alterations of cytosolic viscosity, as suggested by treatments of the attached cells with agents affecting the actin and microtubule cytoskeleton. Our results show that viscosity variations of cells can affect the resonance frequency of QCM in the absence of apparent cell desorption. The simultaneous measurements of the maximal oscillation amplitude, the transient decay time constant and the resonance frequency allow an analysis of cell adsorption to solid substratum in real time and complement cell biological method

Effects of the prewhitening method, the time granularity and the time segmentation on the Mann-Kendall trend detection and the associated Sen's slope

The most widely used non-parametric method for trend analysis is the Mann-Kendall test associated with the Sen's slope. The Mann-Kendall test requires serially uncorrelated time series, whereas most of the atmospheric processes exhibit positive autocorrelation. Several prewhitening methods have been designed to overcome the presence of lag-1 autocorrelation. These include a prewhitening, a detrending and/or a correction for the detrended slope and the original variance of the time series. The choice of which prewhitening method and temporal segmentation to apply has consequences for the statistical significance, the value of the slope and of the confidence limits. Here, the effects of various prewhitening methods are analyzed for seven time series comprising in-situ aerosol measurements (scattering coefficient, absorption coefficient, number concentration and aerosol optical depth), Raman Lidar water vapor mixing ratio and the tropopause and zero degree levels measured by radio-sounding. These time series are characterized by a broad variety of distributions, ranges and lag-1 autocorrelation values and vary in length between 10 and 60 years. A common way to work around the autocorrelation problem is to decrease it by averaging the data over longer time intervals than in the original time series. Thus, the second focus of this study is evaluation of the effect of time granularity on long-term trend analysis. Finally, a new algorithm involving three prewhitening methods is proposed in order to maximize the power of the test, to minimize the amount of erroneous detected trends in the absence of a real trend and to ensure the best slope estimate for the considered length of the time series

Characterization of aerosol hygroscopicity using Raman lidar measurements at the EARLINET station of Payerne

This study focuses on the analysis of aerosol hygroscopicity using remote sensing techniques. Continuous observations of aerosol backscatter coefficient (ßaer), temperature (T) and water vapor mixing ratio (r) have been performed by means of a Raman lidar system at the aerological station of MeteoSwiss at Payerne (Switzerland) since 2008. These measurements allow us to monitor in a continuous way any change in aerosol properties as a function of the relative humidity (RH). These changes can be observed either in time at a constant altitude or in altitude at a constant time. The accuracy and precision of RH measurements from the lidar have been evaluated using the radiosonde (RS) technique as a reference. A total of 172 RS profiles were used in this intercomparison, which revealed a bias smaller than 4¿%¿RH and a standard deviation smaller than 10¿%¿RH between both techniques in the whole (in lower) troposphere at nighttime (at daytime), indicating the good performance of the lidar for characterizing RH. A methodology to identify situations favorable to studying aerosol hygroscopicity has been established, and the aerosol hygroscopicity has been characterized by means of the backscatter enhancement factor (fß). Two case studies, corresponding to different types of aerosol, are used to illustrate the potential of this methodology. The first case corresponds to a mixture of rural aerosol and smoke particles (smoke mixture), which showed a higher hygroscopicity (f355ß=2.8 and f1064ß=1.8 in the RH range 73¿%–97¿%) than the second case, in which mineral dust was present (f355ß=1.2 and f1064ß=1.1in the RH range 68¿%–84¿%). The higher sensitivity of the shortest wavelength to hygroscopic growth was qualitatively reproduced using Mie simulations. In addition, a good agreement was found between the hygroscopic analysis done in the vertical and in time for Case I, where the latter also allowed us to observe the hydration and dehydration of the smoke mixture. Finally, the impact of aerosol hygroscopicity on the Earth's radiative balance has been evaluated using the GAME (Global Atmospheric Model) radiative transfer model. The model showed an impact with an increase in absolute value of 2.4¿W¿m-2 at the surface with respect to the dry conditions for the hygroscopic layer of Case I (smoke mixture).Peer ReviewedPostprint (published version

Towards the profiling of the atmospheric boundary layer at European scale—introducing the COST Action PROBE

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Long-term trends of black carbon and particle number concentration in the lower free troposphere in Central Europe

Background: The implementation of emission mitigation policies in Europe over the last two decades has generally improved the air quality, which resulted in lower aerosol particle mass, particle number, and black carbon mass concentration. However, little is known whether the decreasing particle concentrations at a lower-altitude level can be observed in the free troposphere (FT), an important layer of the atmosphere, where aerosol particles have a longer lifetime and may affect climate dynamics. In this study, we used data from two high-Alpine observatories, Zugspitze-Schneefernerhaus (ZSF) and Jungfraujoch (JFJ), to assess the long-term trends on size-resolved particle number concentrations (PNCs) and equivalent black carbon (eBC) mass concentration separated for undisturbed lower FT conditions and under the influence of air from the planetary boundary layer (PBL) from 2009 to 2018. Results: The FT and PBL-influenced conditions were segregated for both sites. We found that the FT conditions in cold months were more prevalent than in warm months, while the measured aerosol parameters showed different seasonal patterns for the FT and PBL-influenced conditions. The pollutants in the PBL-influenced condition have a higher chance to be transported to high-altitudes due to the mountainous topography, leading to a higher concentration and more distinct seasonal variation, and vice versa. The long-term trends of the measured aerosol parameters were evaluated and the decreased aerosol concentrations were observed for both FT and PBL-influenced conditions. The observed decreasing trends in eBC concentration in the PBL-influenced condition are well consistent with the reported trends in total BC emission in Germany and Switzerland. The decreased concentrations in the FT condition suggest that the background aerosol concentration in the lower FT over Central Europe has correspondingly decreased. The change of back trajectories in the FT condition at ZSF and JFJ was further evaluated to investigate the other possible drivers for the decreasing trends. Conclusions: The background aerosol concentration in the lower FT over Central Europe has significantly decreased during 2009–2018. The implementation of emission mitigation policies is the most decisive factor and the decrease of the regional airmass occurrence over Central Europe also has contributed to the decreasing trends. © 2021, The Author(s)

Climatology of aerosol radiative properties in the free troposphere

Comunicación presentada en: Symposium on Atmospheric Chemistry and Physics at Mountain Sites celebrado del 8 al 10 de junio de 2010 en Interlaken, Suiza

Seasonality of the particle number concentration and size distribution : a global analysis retrieved from the network of Global Atmosphere Watch (GAW) near-surface observatories

Aerosol particles are a complex component of the atmospheric system which influence climate directly by interacting with solar radiation, and indirectly by contributing to cloud formation. The variety of their sources, as well as the multiple transformations they may undergo during their transport (including wet and dry deposition), result in significant spatial and temporal variability of their properties. Documenting this variability is essential to provide a proper representation of aerosols and cloud condensation nuclei (CCN) in climate models. Using measurements conducted in 2016 or 2017 at 62 ground-based stations around the world, this study provides the most up-to-date picture of the spatial distribution of particle number concentration (N-tot) and number size distribution (PNSD, from 39 sites). A sensitivity study was first performed to assess the impact of data availability on N-tot's annual and seasonal statistics, as well as on the analysis of its diel cycle. Thresholds of 50% and 60% were set at the seasonal and annual scale, respectively, for the study of the corresponding statistics, and a slightly higher coverage (75 %) was required to document the diel cycle. Although some observations are common to a majority of sites, the variety of environments characterizing these stations made it possible to highlight contrasting findings, which, among other factors, seem to be significantly related to the level of anthropogenic influence. The concentrations measured at polar sites are the lowest (similar to 10(2) cm(-3)) and show a clear seasonality, which is also visible in the shape of the PNSD, while diel cycles are in general less evident, due notably to the absence of a regular day-night cycle in some seasons. In contrast, the concentrations characteristic of urban environments are the highest (similar to 10(3)-10(4) cm(-3)) and do not show pronounced seasonal variations, whereas diel cycles tend to be very regular over the year at these stations. The remaining sites, including mountain and non-urban continental and coastal stations, do not exhibit as obvious common behaviour as polar and urban sites and display, on average, intermediate N-tot (similar to 10(2)-10(3) cm(-3)). Particle concentrations measured at mountain sites, however, are generally lower compared to nearby lowland sites, and tend to exhibit somewhat more pronounced seasonal variations as a likely result of the strong impact of the atmospheric boundary layer (ABL) influence in connection with the topography of the sites. ABL dynamics also likely contribute to the diel cycle of N-tot observed at these stations. Based on available PNSD measurements, CCN-sized particles (considered here as either >50 nm or >100 nm) can represent from a few percent to almost all of N-tot, corresponding to seasonal medians on the order of similar to 10 to 1000 cm(-3), with seasonal patterns and a hierarchy of the site types broadly similar to those observed for N-tot. Overall, this work illustrates the importance of in situ measurements, in particular for the study of aerosol physical properties, and thus strongly supports the development of a broad global network of near surface observatories to increase and homogenize the spatial coverage of the measurements, and guarantee as well data availability and quality. The results of this study also provide a valuable, freely available and easy to use support for model comparison and validation, with the ultimate goal of contributing to improvement of the representation of aerosol-cloud interactions in models, and, therefore, of the evaluation of the impact of aerosol particles on climate.Peer reviewe

Proteine and cell adsorption: topographical dependency and adlayer viscoelastic properties determined with oscillation amplitude of quartz resonator

La biocompatibilité des matériaux utilisés dans les domaines des implants et des biosenseurs dépend fortement des premières interactions ayant lieu entre une surface donnée et l’environnement biologique. Il est bien connu que lorsqu’un corps vivant est mis en contact avec une surface, une adsorption de protéines est induite (rétention de protéines sur une surface), formant une interface sur laquelle d’autres protéines ou cellules vont adsorber. Les interactions peuvent être influencées en modifiant les propriétés de la surface, qui sont la chimie, la charge et la topographie. Il a été démontré que les cellules sont sensibles à la topographie, se développant le long de rainures de largeurs définies et de profondeurs à l’échelle du micromètre. La question fondamentale abordée dans la première partie de cette thèse est de savoir si les protéines peuvent aussi ”sentir” la topographie à l’échelle du nanomètre, en analogie avec le comportement des cellules. Ces investigations sont particulièrement importantes, puisque des protéines sont toujours présentes entre la surface et les cellules. Les modifications topographiques doivent être effectuées à l’échelle du nanomètre, ce qui correspond à la grandeur des protéines. Avec un Microscope à Force Atomique (AFM) et en appliquant l’Oxidation Anodique Locale (LAO) à air ambiant, il est possible de créer des nanostructures d’une hauteur de 1 - 4nm et d’une largeur de 10nm. La caractérisation de la surface par Spectroscopie Photoélectronique à Rayons-X (XPS) révèle que la LAO assure une modification de la topographie de la surface sans aucun changement de sa composition chimique. Les surfaces structurées par LAO représentent ainsi des systèmes idéaux pour étudier l’adsorption des protéines en fonction de la topographie. Nous pouvons visualiser les nanostructures crées par l’AFM et successivement adsorber les protéines in-situ, rincer et imager la nouvelle surface. La comparaison des densités des protéines adsorbées sur les nanostructures et sur la surface vierge montre que l’arrangement des protéines dépend des nanostructures sous-jacentes. Une remarquable spécificité de l’adsorption de filaments d’actine (F-actine) est notée en fonction de la hauteur des nanostructures. Sur le titane (Ti), la F-actine adsorbe peu sur les lignes de 4nm de haut, et les protéines sont orientées aléatoirement. Au contraire, une grande adsorption de protéines est observée sur les structures ayant des hauteurs comprises entre 1 et 2nm. De plus, les filaments s’adsorbent de préférence parallèlement aux nanostructures. Sur le silicium, la F-actine adsorbe également de préférence le long des lignes de 1nm de haut, cependant la densité des protéines adsorbées est plus grande sur la surface non-structurée. Nous avons ainsi pu démontrer que les protéines sont sensibles à la nanotopographie des surfaces. Les expériences réalisées avec l’AFM ne permettent que des mesures statiques, et ne donnent aucune information quant à la cinétique d’adsorption des protéines. La seconde partie de cette thèse est consacrée à la construction d’une Microbalance à Crystal de Quartz (QCM) qui nous permet tout d’abord de suivre la cinétique d’adsorption, et deuxièmement d’acquérir des informations sur les propriétés viscoélastiques de la couche adsorbée. La QCM est une technique relativement nouvelle mais ultrasensible. Dans les liquides, la QCM peut détecter 9ng/cm2, et cette sensibilité atteint 0.135ng/cm2 dans le vide. Néanmoins, la quantification de la masse adsorbée est difficile à déterminer dans les milieux liquides, car différents phénomènes influencent les paramètres mesurés. Premièrement, les molécules d’eau retenues entre les particules adsorbées apportent leur contribution à la masse mesurée, et deuxièmement, une modification des propriétés du liquide ou de la masse, telles que la densité ou la viscosité, peuvent générer des artefacts. Au contraire des instruments commerciaux, la QCM que nous avons construite permet de mesurer l’amplitude maximale d’oscillation du crystal de quartz. Ce paramètre nous permet de distinguer la contribution due à la masse adsorbée de celle due aux changements de propriétés du liquide et de la masse. L’interprétation des mesures QCM est ainsi améliorée. Dans ce travail de thèse, des expériences ont été réalisées dans les liquides avec différents systèmes, comme des protéines et des cellules, ainsi que sur différentes surfaces. Une plus grande quantité de protéines s’adsorbent sur l’or que sur le Ti. Néanmoins lorsque la concentration des protéines est élevée, l’activité biologique des protéines est plus grande sur le titane. L’adsorption des cellules est régie par des phénomènes complexes qui ne sont pas encore entièrement compris. Nous démontrons que, durant les 80 premières minutes d’adsorption, l’expansion des cellules influence principalement les paramètres mesurés. Ensuite le cytosquelette est développé, induisant une rigidification de la cellule, ce qui augmente la viscosité totale de la cellule. Ce phénomène induit des variations de la fréquence, de l’amplitude et de la constante d’amortissement malgré qu’aucune modification réelle de la quantité de cellules adsorbées n’ait lieu. En utilisant des drogues, il a été possible de modifier l’état de polymérisation du cytosquelette, ce qui induit des changements des propriétés viscoélastiques des cellules adsorbées. Les changements de fréquence, d’amplitude et de constante d’amortissement mesurés durant l’expansion cellulaire ont ainsi pu être reproduits. En résumé, la topographie est un paramètre important qui doit être pris en considération dans le domaine général des biomatériaux, car la structure de la surface à l’échelle du nanomètre peut influencer la réponse d’un environnement biologique. Afin de mieux analyser l’adsorption de protéines et la réponse cellulaire envers des surfaces, la QCM est une technique très prometteuse, permettant non seulement de mesurer la masse adsorbée, mais aussi le développement des cellules. Il est cependant essentiel de mesurer plusieurs paramètres.The biocompatibility of materials in implant or biosensor fields strongly depends on first interactions occurring between a given surface and a biological environment. It is well-known that a living body brought into contact with a surface will induce protein adsorption, which creates the interface, on which proteins or cells will adsorb. The interactions can be influenced by modifying the surface properties, which are the chemistry, the surface charge and the topography of the surface. It has been shown that cells can “sense” the topography, growing along grooves of defined depth and width at the micrometer scale. In the first part of this thesis, the fundamental addressed question is whether proteins can ”sense” the topography, in analogy to what has been observed for cells on microstructures, because proteins are always present between the surface and the cells. Topographical modification have to be performed at the nanometer scale, corresponding to the size of proteins. Using an Atomic Force Microscope (AFM) and applying Local Anodic Oxidation (LAO) in ambient air, it is possible to create nanostructures of a height of 1 - 4nm and a width of 10nm. The characterization of the surface by X-Ray Photoelectron Spectroscopy (XPS) reveals that this method assures a modification of the topography of the surface without change of its chemical composition. Surfaces structured by LAO therefore represent ideal systems to study the dependence of protein adsorption on topography. We are able to visualize the created nanostructures by AFMand successively adsorb proteins in situ, rinse and image the new surface. The densities of adsorbed proteins on the nanostructured and neat surfaces are compared and we find that the protein arrangement depends on the underlying nanostructures. A remarkable specificity of the actin filament (F-actin) adsorption on the nanostructure height is noticed. On Ti, F-actin is observed to have a low adsorption on created lines of a height of 4nm and the adsorbed proteins appear to be randomly oriented. In contrast, high protein adsorption is observed for structure height between 1 and 2nm, moreover the filaments adsorb preferentially parallel to the nanostructured pattern. On Si, F-actin also adsorb preferentially along 1nm high lines, but the density of adsorbed proteins is higher on neat surface. We have therefore demonstrated that proteins “sense” the topography of surfaces at the nanometer scale. Experiments performed with AFM only permit static measurements giving no information on the kinetics of protein adsorption. The second part of this thesis is devoted to the building of a Quartz Crystal Microbalance (QCM), which allows us firstly to follow the adsorption kinetics, and secondly to get information about the viscoelastic properties of the adlayer. The QCM is a rather new but ultrasensitive technique. In liquid the QCM sensitivity is 9ng/cm2 and under vacuum it reaches 0.135ng/cm2. Nevertheless quantification of the amount of adsorbed mass is still difficult to determine under liquid loading, since different phenomena influence the measured parameters. Water molecules entrapped between adsorbed mass can firstly bring an added measured mass, and secondly modification of the liquid and mass properties such as density and viscosity can bring artefacts. In contrary to commercial instruments, our home-made QCM allows us to measure the maximal oscillation amplitude of the quartz crystal. This parameter allows us to distinguish the contribution due to adsorbed mass from the one due to changes of liquid and mass properties. The interpretation of the QCM measurements is therefore enhanced. During this thesis work experiments have been performed under liquid with different systems, such as proteins and cells, and on different surfaces. On Au more proteins adsorb on the surface, in comparison to Ti. Nevertheless the biological activity is larger on Ti at high protein concentration. Adsorption of cells involves complex phenomena, which are not yet fully determined. We demonstrate that during the first 80mn of adsorption, the spreading of the cell influences mostly the measured parameters. Thereafter the cytoskeleton of the cell is rearranged, inducing cell stiffening and an increase of the total cell viscosity. This phenomenon induces variations of the frequency, the amplitude and the decay time constant, although no real modification of the amount of adsorbed cell occurs. Using drugs, it has been possible to modify the polymerisation state of the cytoskeleton, inducing changes of the viscoelastic properties of the adsorbed cells. Changes of the measured frequency, amplitude and decay time constant during cell spreading could therefore be reproduced. In summary the topography is an important parameter, which has to be taken into account in the general biomaterial field, because the structure of the surface at a nanometer scale can influence the response of biological environments. In order to better analyze the protein adsorption and the cell response against surfaces, the QCM is a very promising technique, but it is essential to measure several parameters

Polymers and Cold Plasmas

In the last 15 years the use of plasma for materials processing has received a great amount of interest. The scope of possible applications is expanding rapidly and covers a large range of different fields. Applications may be found in microelectronics, food packaging, decorative and functional coatings; many different materials as metals, semiconductors, ceramics or polymers are involved by the plasma technology as bulk material, surface or interface. Plasma treatment is probably the most versatile surface treatment technique. Different types of gases such as argon, oxygen, nitrogen, fluorine, water etc. can produce the unique surface properties required by various applications. For example, O2 plasma treatment can increase the surface energy of polymers, whereas fluorine-containing plasma treatment can decrease the surface energy and improve the chemical inertness. Cross-linking at a polymer surface can be introduced by noble gas plasmas. Thin polymer films with unique chemical and physical properties are produced by plasma polymerisation. This technology is still in its infancy, and the plasma chemical process is not fully understood. The present article gives a short and non-exhaustive introduction on plasma polymer interaction and our activities in this field