| 1. |
- Alrifaiy, Ahmed
(author)
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Lab on a chip for electrophysiological measurements with control of the oxygen content : optical manipulation and spectroscopic analysis of biological cells
- 2013
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Doctoral thesis (other academic/artistic)abstract
- Stroke affects nearly 20 million people around the world every year. Clinically, stroke is a result of brain damage due to the shortage of oxygen delivered to the nerve cells. To minimize suffering and costs related to the disease, extensive research is performed on different levels. The focus of our research is to achieve fundamental understanding on how the lack of oxygen in brain tissue activates intrinsic biomolecular defense mechanisms that may reduce brain damage. More knowledge may hopefully lead to new therapeutic and preventive strategies on the molecular level for individuals in the risk zone for stroke or those who have just suffered a stroke.The area of study is based on the discovery of a hemoprotein called neuroglobin (Ngb), which is found in various regions in the brain, in the islets of Langerhans, and in the retina. Several studies have shown that Ngb seems to have a protective function against hypoxia-related damage. However, until now, it has not been understood how Ngb affects the nerve system and protects neurons from damage.The well-established patch-clamp technique is routinely used to measure and analyze the electrophysiological activity of individual biological cells. To perform accurate patchclamp experiments, it is important to create well-controlled physiological conditions, i.e. different oxygen levels and fast changes of nutrients and other biochemical substances. A promising approach is to apply lab on a chip technologies combined with optical manipulation techniques. These give optimal control over fast changing environmental conditions and enable multiple readouts.The conventional open patch-clamp configuration cannot provide adequate control of the oxygen content. Therefore, the aim of the thesis was to design and test a multifunctional microfluidic system, lab on a chip (LOC), that can achieve normoxic, anoxic and hypoxic conditions. The conventional patch clamp configuration was substituted by a gas-tight LOC system with an integrated patch-clamp micropipette. The system was combined with optical tweezers, optical sensor and optical spectroscopy.Optical tweezers were used to trap and guide single cells through the LOC microchannels towards the fixed micropipette. Optical spectroscopy was essential to investigate the biochemical composition of the biological samples. The developed, gas-tight LOC acted as a multifunctional system for simultaneous electrophysiological and spectroscopic experiments with good control over the oxygen content in the liquid perifusing the cells. The system was tested in series of experiments: optically trapped cells (red blood cells from human and chicken and nerve cells) were steered to the fixed patch-clamp pipette within the LOC system. The oxygen content within the microfluidic channels was measured to ∼ 1% compared to the usual 4-7% found in open system. The trapping dynamics were monitored in real-time while the spectroscopic measurements were performed simultaneously to acquire absorption spectra of the trapped cell under varying environments. To measure the effect of the laser tweezers on the sample, neurons from rats in a Petri dish were optically trapped and steered towards the patch-clamp micropipette where electrophysiological investigations were performed. The optical tweezers had no effect on the electrophysiological measurements.The future aim is to perform complete protocols of patch-clamp electrophysiological investigations while simultaneously monitoring the biochemical composition of the sample by optical spectroscopy. The straightforwardness and stability of the microfluidic chip have shown excellent potential to be applied for various biomedical applications. The subsequent ambition is to use this system as a mini laboratory that has benefits in cell sorting, patch-clamp and fertilization experiments where the gaseous and the biochemical content is of importance.The long-term goal is to study the response of individual neurons and defense mechanisms under hypoxic conditions that may establish new ways to understand cell behavior related to Ngb for various diseases such as stroke, Alzheimer’s and Parkinson’s.
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| 2. |
- Andersson, Magnus, et al.
(author)
-
A sticky chain model of the elongation and unfolding of escherichia coli P pili under stress
- 2006
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In: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 90:5, s. 1521-1534
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Journal article (peer-reviewed)abstract
- A model of the elongation of P pili expressed by uropathogenic Escherichia coli exposed to stress is presented. The model is based upon the sticky chain concept, which is based upon Hooke’s law for elongation of the layer-to-layer and head-to-tail bonds between neighboring units in the PapA rod and a kinetic description of the opening and closing of bonds, described by rate equations and an energy landscape model. It provides an accurate description of the elongation behavior of P pili under stress and supports a hypothesis that the PapA rod shows all three basic stereotypes of elongation/unfolding: elongation of bonds in parallel, the zipper mode of unfolding, and elongation and unfolding of bonds in series. The two first elongation regions are dominated by a cooperative bond opening, in which each bond is influenced by its neighbor, whereas the third region can be described by individual bond opening, in which the bonds open and close randomly. A methodology for a swift extraction of model parameters from force-versus-elongation measurements performed under equilibrium conditions is derived. Entities such as the free energy, the stiffness, the elastic elongation, the opening length of the various bonds, and the number of PapA units in the rod are determined.
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| 3. |
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| 4. |
- Andersson, Magnus, 1975-
(author)
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Construction of force measuring optical tweezers instrumentation and investigations of biophysical properties of bacterial adhesion organelles
- 2007
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Doctoral thesis (other academic/artistic)abstract
- Optical tweezers are a technique in which microscopic-sized particles, including living cells and bacteria, can be non-intrusively trapped with high accuracy solely using focused light. The technique has therefore become a powerful tool in the field of biophysics. Optical tweezers thereby provide outstanding manipulation possibilities of cells as well as semi-transparent materials, both non-invasively and non-destructively, in biological systems. In addition, optical tweezers can measure minute forces (< 10-12 N), probe molecular interactions and their energy landscapes, and apply both static and dynamic forces in biological systems in a controlled manner. The assessment of intermolecular forces with force measuring optical tweezers, and thereby the biomechanical structure of biological objects, has therefore considerably facilitated our understanding of interactions and structures of biological systems. Adhesive bacterial organelles, so called pili, mediate adhesion to host cells and are therefore crucial for the initial bacterial-cell contact. Thus, they serve as an important virulence factor. The investigation of pili, both their biogenesis and their expected in vivo properties, brings information that can be of importance for the design of new drugs to prevent bacterial infections, which is crucial in the era of increased bacterial resistance towards antibiotics. In this thesis, an experimental setup of a force measuring optical tweezers system and the results of a number of biomechanical investigations of adhesive bacterial organelles are presented. Force measuring optical tweezers have been used to characterize three different types of adhesive organelles under various conditions, P, type 1, and S pili, which all are expressed by uropathogenic Escherichia coli. A quantitative biophysical force-extension model, built upon the structure and force response, has been developed. It is found, that this model describes the biomechanical properties for all three pili in an excellent way. Various parameters in their energy landscape, e.g., bond lengths and transition barrier heights, are assessed and the difference in behavior is compared. The work has resulted in a method that in a swift way allows us to probe different types of pili with high force and high spatial resolution, which has provided an enhanced understanding of the biomechanical function of these pili.
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| 5. |
- Andersson, Magnus, et al.
(author)
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Dynamic Force Spectroscopy of E. coli P Pili
- 2006
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In: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 91:7, s. 2717-2725
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Journal article (peer-reviewed)abstract
- Surface organelles (so-called pili) expressed on the bacterial membrane mediate the adhesion of Escherichia coli causing urinary tract infection. These pili possess some extraordinary elongation properties that are assumed to allow a close bacterium-to-host contact even in the presence of shear forces caused by urine flow. The elongation properties of P pili have therefore been assessed for low elongation speeds (steady-state conditions). This work reports on the behavior of P pili probed by dynamic force spectroscopy. A kinetic model for the unfolding of a helixlike chain structure is derived and verified. It is shown that the unfolding of the quaternary structure of the PapA rod takes place at a constant force that is almost independent of elongation speed for slow elongations (up to ~0.4 μm/s), whereas it shows a dynamic response with a logarithmic dependence for fast elongations. The results provide information about the energy landscape and reaction rates. The bond length and thermal bond opening and closure rates for the layer-to-layer bond have been assessed to ~0.76 nm, ~0.8 Hz, and ~8 GHz, respectively. The results also support a previously constructed sticky-chain model for elongation of the PapA rod that until now had been experimentally verified only under steady-state conditions.
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| 6. |
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| 7. |
- Andersson, Magnus, et al.
(author)
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Force measuring optical tweezers system for long time measurements of P pili stability
- 2006
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In: Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IV. - : SPIE. - 081946130X - 9780819461308 ; , s. 608810-
-
Conference paper (peer-reviewed)abstract
- A force-measuring optical tweezers instrumentation and long time measurements of the elongation and retraction of bacterial fimbriae from Uropathogenic E. coli (UPEC) under strain are presented. The instrumentation is presented in some detail. Special emphasis is given to measures taken to reduce the influence of noise and drifts in the system and from the surrounding, which makes long term force measurements possible. Individual P pili from UPEC bacteria were used as a biological model system for repetitive unfolding and refolding cycles of bacterial fimbriae under equilibrium conditions. P pili have evolved into a three-dimensional helix-like structure, the PapA rod, that can be successively and significantly elongated and/or unfolded when exposed to external forces. The instrumentation is used for characterization of the force-vs.-elongation response of the PapA rod of individual P pili, with emphasis on the long time stability of the forced unfolding and refolding of the helical structure of the PapA rod. The results show that the PapA rod is capable of withstanding extensive strain, leading to a complete unfolding of the helical structure, repetitive times during the life cycle of a bacterium without any noticeable alteration of the mechanical properties of the P pili. This function is believed to be importance for UPEC bacteria in vivo since it provides a close contact to a host cell (which is an initial step of invasion) despite urine cleaning attempts.
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| 8. |
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| 9. |
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| 10. |
- Andersson, Magnus, et al.
(author)
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Physical Properties of Biopolymers Assessed by Optical Tweezers : Analysis of folding and refolding of bacterial pili
- 2008
-
In: ChemPhysChem. - : Wiley-VCH Verlagsgesellschaft. - 1439-4235 .- 1439-7641. ; 9:2, s. 221-235
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Journal article (peer-reviewed)abstract
- Bacterial adhesion to surfaces mediated by specific adhesion organelles that promote infections, as exemplified by the pili of uropathogenic E. coli, is studied mostly at the level of cell-cell interactions and thereby reflects the averaged behavior of multiple pili. The role of pilus rod structure has therefore only been estimated from the outcome of experiments involving large numbers of organelles at the same time. It has, however, lately become clear that the biomechanical behavior of the pilus shafts play an important, albeit hitherto rather unrecognized, role in the adhesion process. For example, it has been observed that shafts from two different strains, even though they are similar in structure, result in large differences in the ability of the bacteria to adhere to their host tissue. However, in order to identify all properties of pilus structures that are of importance in the adhesion process, the biomechanical properties of pili must be assessed at the single-molecule level. Due to the low range of forces of these structures, until recently it was not possible to obtain such information. However, with the development of force-measuring optical tweezers (FMOT) with force resolution in the low piconewton range, it has lately become possible to assess forces mediated by individual pili on single living bacteria in real time. FMOT allows for a more or less detailed mapping of the biomechanical properties of individual pilus shafts, in particular those that are associated with their elongation and contraction under stress. This Mi- nireview presents the FMOT technique, the biological model system, and results from assessment of the biomechanical properties of bacterial pili. The information retrieved is also compared with that obtained by atomic force microscopy.
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| 11. |
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| 12. |
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| 13. |
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| 14. |
- Axner, Ove, et al.
(author)
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A discussion about the significance of absorbance and sample optical thickness in conventional absorption spectrometry and wavelength-modulated laser absorption spectrometry
- 2003
-
In: Spectrochimica Acta Part B - Atomic Spectroscopy. - : Elsevier. - 0584-8547 .- 1873-3565. ; 58:11, s. 1997-2014
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Journal article (peer-reviewed)abstract
- One of the most frequently used concepts in atomic absorption spectrometry (AAS) is that of Absorbance, an easily measurable quantity that is linear with the concentration of the analyte over a large range of concentrations whenever Beer's law is valid. Laser-based modulation techniques, however, in particular wavelength modulated diode laser absorption spectrometry (WMAS), do not measure exactly the same physical quantities as conventional AAS techniques do, since they do not rely upon separate measurements of the intensities in the presence and in the absence of the sample, but rather (a certain fraction of) the difference between the signals 'on' and 'off' resonance. Hence, Absorbance is not as natural for the modulated laser-based absorption techniques as it is for the conventional AAS techniques. The entity called sample optical thickness (SOT) appears to be a natural entity as well as a natural unit (denoted SOT units) for the quantification of signals in WMAS. The present paper discusses the concept of measurable quantities and their units in WMAS in some detail and compares them (theoretical and practical considerations) with those of conventional AAS. In particular, it makes a distinction between the 'observed' sample optical thickness and the 'true' sample optical thickness and shows how these two entities are related to the Absorbance entity. Finally, this work also introduces a dimensionless sensitivity of the WMAS technique, and shows this quantity to be equal to the nth Fourier coefficient of the wavelength modulated, peak-normalized line shape function.
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| 15. |
- Axner, Ove, et al.
(author)
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A general non-complex analytical expression for the nth Fourier component of a wavelength-modulated Lorentzian lineshape function
- 2001
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In: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier. - 0022-4073 .- 1879-1352. ; 68:3, s. 299-317
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Journal article (peer-reviewed)abstract
- A general, analytical expression for the nth Fourier component of a wavelength-modulated Lorentzian lineshape function in terms of a normalized detuning and a normalized modulation amplitude is derived. The expression is cast in a purely real form and is therefore easier to use than the normally used expression, which is given in terms of various combinations (sums, square roots, and powers) of complex expressions and their complex conjugates. Analytical expressions for the nine first Fourier components (n = 0,...,8), clearly showing their dependence on normalized detuning and modulation amplitude, are explicitly given. Simplified expressions for the even harmonics of the Fourier components on resonance, at which they take their maximum value, solely given in terms of the normalized modulation amplitude, are also explicitly given. It is shown that previously published, numerically calculated conditions for maximization of higher-order Fourier components are incorrect. The normalized modulation amplitudes that maximize the four lowest even harmonics of the Fourier components, i.e. for n = 2, 4, 6, and 8, are 2.20, 4.12, 6.08, and 8.06, respectively.
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| 16. |
- Axner, Ove, et al.
(author)
-
Ability of gas modulation to reduce the pickup of drifts in refractometry
- 2021
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In: Journal of the Optical Society of America. B, Optical physics. - : Optical Society of America. - 0740-3224 .- 1520-8540. ; 38:8, s. 2419-2436
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Journal article (peer-reviewed)abstract
- Gas modulation refractometry (GAMOR) is a methodology for assessment of gas refractivity, molar density, and pressure that, by a rapid gas modulation, exhibits a reduced susceptibility to various types of disturbances. Although previously demonstrated experimentally, no detailed analysis of its ability to reduce the pickup of drifts has yet been given. This work provides an explication of to what extent modulated refractometry in general, and GAMOR in particular, can reduce drifts, predominantly those of the cavity lengths, gas leakages, and outgassing. It is indicated that the methodology is insensitive to the linear parts of so-called campaign-persistent drifts and that it has a significantly reduced susceptibility to others. This makes the methodology suitable for high-accuracy assessments and out-of-laboratory applications.
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| 17. |
- Axner, Ove, et al.
(author)
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Ability of gas modulation to reduce the pickup of drifts in refractometry
- 2021
-
In: Journal of the Optical Society of America. B, Optical physics. - : Optica Publishing Group. - 0740-3224 .- 1520-8540. ; 38:8, s. 2419-2436
-
Journal article (peer-reviewed)abstract
- Gas modulation refractometry (GAMOR) is a methodology for assessment of gas refractivity, molar density, and pressure that, by a rapid gas modulation, exhibits a reduced susceptibility to various types of disturbances. Although previously demonstrated experimentally, no detailed analysis of its ability to reduce the pickup of drifts has yet been given. This work provides an explication of to what extent modulated refractometry in general, and GAMOR in particular, can reduce drifts, predominantly those of the cavity lengths, gas leakages, and outgassing. It is indicated that the methodology is insensitive to the linear parts of so-called campaign-persistent drifts and that it has a significantly reduced susceptibility to others. This makes the methodology suitable for high-accuracy assessments and out-of-laboratory applications
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| 18. |
- Axner, Ove, et al.
(author)
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Ability of gas modulation to reduce the pickup of fluctuations in refractometry
- 2020
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In: Journal of the Optical Society of America. B, Optical physics. - : OSA - The Optical Society. - 0740-3224 .- 1520-8540. ; 37:7, s. 1956-1965
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Journal article (peer-reviewed)abstract
- Gas modulation refractometry is a technique for assessment of gas refractivity, density, and pressure that, by a rapid modulation of the gas, provides a means to significantly reduce the pickup of fluctuations. Although its unique feature has previously been demonstrated, no detailed explication or analysis of this ability has yet been given. This work provides a theoretical explanation, in terms of the length of the modulation cycle, of the extent to which gas modulation can reduce the pickup of fluctuations. It is indicated that a rapid modulation can significantly reduce the influence of fluctuations with Fourier frequencies lower than the inverse of the modulation cycle length, which often are those that dominate. The predictions are confirmed experimentally
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| 19. |
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| 20. |
- Axner, Ove, et al.
(author)
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Absorption spectrometry by narrowband light in optically saturated and optically pumped collision and doppler broadened gaseous media under arbitrary optical thickness conditions
- 2006
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In: Applied Spectroscopy. - New York : Society for applied spectroscopy. - 0003-7028 .- 1943-3530. ; 60:11, s. 1217-1240
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Journal article (peer-reviewed)abstract
- This work examines absorption spectrometry by narrowband light in gaseous media with arbitrary optical thickness when the light induces optical saturation or optical pumping. Two quantities are defined: the observed absorbance, Aobs, and the true absorbance, Atrue. The former is the absorbance that is measured under the existing conditions, whereas the latter represents the absorbance one would measure if the light acted solely as a probe of the populations of the various levels, and it is therefore directly proportional to the concentration or density of absorbers. A general integral equation for the propagation of light in media of arbitrary optical thickness in which the light influences the populations of the levels involved is derived. This expression is transcendental in the observed absorbance and cannot be solved analytically. It is shown that an analytical expression can be derived by investigating the inverse relationship, i.e., Atrue = f(Aobs). Inasmuch as collision and Doppler broadened media react differently to optical saturation, they are considered separately. It is shown that a nonlinear response results if the medium is optically saturated (or pumped) and not optically thin. Expressions for the error introduced if the technique of standard additions is uncritically applied to such a system are derived.
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| 21. |
- Axner, Ove, 1957-, et al.
(author)
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Assessing bacterial adhesion on an individual adhesin and single pili level using optical tweezers
- 2011
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In: Bacterial adhesion. - Berlin : Springer Berlin/Heidelberg. ; , s. 301-313
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Book chapter (peer-reviewed)abstract
- Optical tweezers (OT) are a technique that, by focused laser light, can both manipulate micrometer sized objects and measure minute forces (in the pN range) in biological systems. The technique is therefore suitable for assessment of bacterial adhesion on an individual adhesin-receptor and single attachment organelle (pili) level. This chapter summarizes the use of OT for assessment of adhesion mechanisms of both non-piliated and piliated bacteria. The latter include the important helix-like pili expressed by uropathogenic Escherichia coli (UPEC), which have shown to have unique and intricate biomechanical properties. It is conjectured that the large flexibility of this type of pili allows for a redistribution of an external shear force among several pili, thereby extending the adhesion lifetime of bacteria. Systems with helix-like adhesion organelles may therefore act as dynamic biomechanical machineries, enhancing the ability of bacteria to withstand high shear forces originating from rinsing flows such as in the urinary tract. This implies that pili constitute an important virulence factor and a possible target for future anti-microbial drugs.
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| 22. |
- Axner, Ove, et al.
(author)
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Assessment of gas molar density by gas modulation refractometry : A review of its basic operating principles and extraordinary performance
- 2021
-
In: Spectrochimica Acta Part B - Atomic Spectroscopy. - : Elsevier B.V.. - 0584-8547 .- 1873-3565. ; 179
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Journal article (peer-reviewed)abstract
- A technique for high-precision and high-accuracy assessment of both gas molar (and number) density and pressure, Gas Modulation Refractometry (GAMOR), is presented. The technique achieves its properties by assessing refractivity as a shift of a directly measurable beat frequency by use of Fabry-Perot cavity (FPC) based refractometry utilizing the Pound-Drever-Hall laser locking technique. Conventional FPC-based refractometry is, however, often limited by fluctuations and drifts of the FPC. GAMOR remedies this by an additional utilization of a gas modulation methodology, built upon a repeated filling and evacuation of the measurement cavity together with an interpolation of the empty cavity responses. The procedure has demonstrated an ability to reduce the influence of drifts in a non-temperature stabilized dual-FPC (DFPC)-based refractometry system, when assessing pressure, by more than three orders of magnitude. When applied to a DFPC system with active temperature stabilization, it has demonstrated, for assessment of pressure of N2 at 4304 Pa at room temperature, which corresponds to a gas molar density of 1.7 × 10−6 mol/cm3, a sub-0.1 ppm precision (i.e. a resolution of 0.34 mPa). It is claimed that the ability to assess gas molar density is at least as good as so far has been demonstrated for pressure (i.e. for the molar density addressed, a resolution of at least 1.2 × 10−13 mol/cm3). It has recently been argued that the methodology should be capable of providing an accuracy that is in the low ppm range. These levels of precision and accuracy are unprecedented among laser-based techniques for detection of atomic and molecular species. Since the molar polarizability of He can be calculated by ab initio quantum mechanical calculations with sub-ppm accuracy, it can also be used as a primary or semi-primary standard of both gas molar (and number) density and pressure. © 2021 The Author(s)
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| 23. |
- Axner, Ove, et al.
(author)
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Authors’ reply
- 2004
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In: Spectrochimica Acta, Part B. ; 59:3, s. 390-392
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Journal article (peer-reviewed)
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| 24. |
- Axner, Ove, 1957-, et al.
(author)
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Laser spectrometric techniques in analytical atomic spectrometry
- 2012
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In: Encyclopedia of analytical chemistry. - Chichester, UK : John Wiley & Sons, Ltd. - 9780470027318
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Book chapter (peer-reviewed)abstract
- The main purpose of this article is to describe the theory, instrumentation, and analytical performance of laser analytical atomic spectrometry, focusing on absorption, fluorescence, and ionization techniques. The structure of the article is such that it first provides an outline of the theory of light-matter interactions that prevail for each type of technique as well as of the most common modulation techniques, primarily, wavelength modulation (WM). This is followed by a section that covers the most important types of instrumentation used. The article finally provides a detailed discussion on the specific instrumentation, mode of operation, use, performance, and applications (both analytical and diagnostic) of each technique. In terms of laser atomic absorption, the focus of the discussion is on the use of approaches to enhance the detection capability by either reducing the amount of noise (as is done by the wavelength modulation absorption spectrometry (WMAS) technique) or by providing an extended interaction length (giving rise to cavity-enhanced absorption spectrometry (CEAS) techniques in general, and cavity ring-down spectrometry (CRDS) in particular). Laser atomic fluorescence techniques (often referred to as laser-excited atomic fluorescence spectrometry (LEAFS)) as well as laser ionization techniques (termed either laser-enhanced ionization (LEI) or resonance ionization spectrometry (RIS)) are also covered in some detail. It is shown that several of these techniques are capable of detecting a variety of elements in liquid samples down to low picogram per milliliter (pg mL−1) or parts-per-trillion (ppt) concentrations and in low femtogram amounts. Also other properties of the techniques, e.g. selectivity and linear dynamic range (LDR), are in general superior to those of conventional (nonlaser-based techniques).
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| 25. |
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| 26. |
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| 27. |
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| 28. |
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| 29. |
- Axner, Ove, 1957-, et al.
(author)
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NICE-OHMS – frequency modulation cavity-enhanced spectroscopy : principles and performance
- 2014
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In: Cavity-Enhanced Spectroscopy and Sensing. - Berlin : Springer Berlin/Heidelberg. - 9783642400025 - 9783642400032 ; , s. 221-251
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Book chapter (peer-reviewed)abstract
- Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is a sensitive technique for detection of molecular species in gas phase. It is based on a combination of frequency modulation for reduction of noise and cavity enhancement for prolongation of the interaction length between the light and a sample. It is capable of both Doppler-broadened and sub-Doppler detection with absorption sensitivity down to the 10−12 and 10−14 Hz−1/2 cm−1 range, respectively. This chapter provides a thorough description of the basic principles and the performance of the technique.
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| 30. |
- Axner, Ove, 1957-, et al.
(author)
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Noise-immune cavity-enhanced analytical atomic spectrometry — NICE-AAS : a technique for detection of elements down to zeptogram amounts
- 2014
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In: Spectrochimica Acta Part B - Atomic Spectroscopy. - : Elsevier. - 0584-8547 .- 1873-3565. ; 100, s. 211-235
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Journal article (peer-reviewed)abstract
- Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is a powerful technique for detection of molecular compounds in gas phase that is based on a combination of two important concepts: frequency modulation spectroscopy (FMS) for reduction of noise, and cavity enhancement, for prolongation of the interaction length between the light and the sample. Due to its unique properties, it has demonstrated unparalleled detection sensitivity when it comes to detection of molecular constituents in the gas phase. However, despite these, it has so far not been used for detection of atoms, i.e. for elemental analysis. The present work presents an assessment of the expected performance of Doppler-broadened (Db) NICE-OHMS for analytical atomic spectrometry, then referred to as noise-immune cavity-enhanced analytical atomic spectrometry (NICE-AAS). After a description of the basic principles of Db-NICE-OHMS, the modulation and detection conditions for optimum performance are identified. Based on a previous demonstrated detection sensitivity of Db-NICE-OHMS of 5×10−12 cm−1 Hz−1∕2 (corresponding to a single-pass absorbance of 7×10−11 over 10 s), the expected limits of detection (LODs) of Hg and Na by NICE-AAS are estimated. Hg is assumed to be detected in gas phase directly while Na is considered to be atomized in a graphite furnace (GF) prior to detection. It is shown that in the absence of spectral interferences, contaminated sample compartments, and optical saturation, it should be feasible to detect Hg down to 10 zg/cm3 (10 fg/m3 or 10-5 ng/m3), which corresponds to 25 atoms/cm3, and Na down to 0.5 zg (zg = zeptogram = 10-21 g), representing 50 zg/mL (parts-per-sextillion, pps, 1:1021) in liquid solution (assuming a sample of 10 µL) or solely 15 atoms injected into the GF, respectively. These LODs are several orders of magnitude lower (better) than any previous laser-based absorption technique previously has demonstrated under atmospheric pressure conditions. It is prophesied that NICE-AAS could provide such high detection sensitivity that the instrumentation should not, by itself, be the limiting factor of an assessment of elemental abundance; the accuracy of an assessment would then instead be limited by concomitant species, e.g. originating from the handling procedures of the sample or the environment.
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| 31. |
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| 32. |
- Axner, Ove, et al.
(author)
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Sub-Doppler dispersion and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy revised
- 2008
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In: Journal of the Optical Society of America B. ; 25:7, s. 1166-1177
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Journal article (peer-reviewed)abstract
- An expression for the peak-to-peak sub-Doppler optical phase shift of two counter-propagating modes of light, to which the noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) dispersion signal is proportional, valid for arbitrary degree of saturation, is derived. For low degrees of saturation it agrees with the expression for weakly saturating (ws) conditions, [(1+S)-1/2-(1+2S)-1/2]α0/2, where S is the degree of saturation and α0 the unsaturated peak absorption. However, the new expression, which can be written as 0.45S(1+S)-1α0/2, does not predict a distinct maximum as the ws-expression does; instead it predicts an optical phase shift that increases monotonically with S and levels off to 0.45α0/2 for large S. This alters the optimum conditions for the sub-Doppler NICE-OHMS technique and improves its shot-noise-limited detectability. The new expression is based upon the same explicit assumptions as the ws-expression but not the Kramers-Kronig’s relations, which are not valid for nonlinear responses, and is supported by experimental results up to S = 100. The new expression is expected to be valid for all techniques measuring sub-Doppler dispersion signals
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| 33. |
- Axner, Ove, et al.
(author)
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Unraveling the secrets of bacterial adhesion organelles using single-molecule force spectroscopy
- 2010
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In: Single molecule spectroscopy in chemistry, physics and biology. - Berlin, Heidelberg : Springer. - 9783642025969 ; , s. 337-362
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Conference paper (peer-reviewed)abstract
- Many types of bacterium express micrometer-long attachment organelles (so-called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Force-measuring optical tweezers (FMOT) have since then been used to unravel the biomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin situated at the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g., urine flow. It has been found that many types of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.
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| 34. |
- Axner, Ove, et al.
(author)
-
Unraveling the secrets of bacterial adhesion organelles using single molecule force spectroscopy
- 2010. - 96
-
In: Springer series in chemical physics. - : Springer Verlag. - 9783642025969 ; , s. 337-362
-
Book chapter (other academic/artistic)abstract
- Many types of bacterium express micrometer-long attachment organelles (so called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Forcemeasuring ptical tweezers (FMOT) have since then been used to unravel the iomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin situated and the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g. urine flow. It has been found that anytypes of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.
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| 35. |
- Bengtsson, Lars, 1963, et al.
(author)
-
The use of autoionizing states for efficient detection of Sr in resonance ionization mass spectrometry
- 1991
-
In: Institute of Physics Conference Series. - 0951-3248. ; 114:9, s. 377-380
-
Journal article (peer-reviewed)abstract
- An efficient excitation scheme for RIMS of Sr has been investigated. Two-colour excitation has been used for excitation of the atoms to an autoionization level with both transitions in the visible region. The first step excitation was at 460.733 nm (5s2 1S0 -> 5s5p 1P1) and the second step leading to ionization was at 405.32 nm which connects the first excited state with a 1D2 autoionizing state at 46380 cm-1. This type of RIMS excitation scheme ensures selectively in both steps as well as an efficient degree of ionization. The choice of the visible wavelength helps also to minimize the influence of spectral interference as well as wing excitations of matrix species.
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| 36. |
- Björnham, Oscar, 1976-
(author)
-
A study of bacterial adhesion on a single-cell level by means of force measuring optical tweezers and simulations
- 2009
-
Doctoral thesis (other academic/artistic)abstract
- The intriguing world of microbiology is nowadays accessible for detailed exploration at a single–molecular level. Optical tweezers are a novel instrument that allows for non–invasive manipulation of single cells by the sole use of laser light and operates on the nano– and micrometer scale which corresponds to the same length scale as living cells. Moreover, forces within the field of microbiology are typically in the picoNewton range which is in accordance with the capability of force measuring optical tweezers systems. Both these conformabilities imply that force measuring optical tweezers is suitable for studies of single living cells. This thesis focuses on the mechanisms of bacterial attachments to host cells which constitute the first step in bacterial infection processes. Bacteria bind specifically to host receptors by means of adhesins that are expressed either directly on the bacterial membrane or on micrometer–long adhesion organelles that are called pili. The properties of single adhesin–receptor bonds that mediate adherence of the bacterium Helicobacter pylori are first examined at various acidities. Further on, biomechanical properties of P pili expressed by Escherichia coli are presented to which computer simulations, that capture the complex kinetics of the pili structure and precisely replicate measured data, are applied. Simulations are found to be a powerful tool for investigations of adhesive attributes of binding systems and are utilized in the analyses of the specific binding properties of P pili on a single–pilus level. However, bacterial binding systems generally involve a multitude of adhesin–receptor bonds. To explore bacterial attachments, the knowledge from single–pilus studies is brought into a full multipili attachment scenario which is analyzed by means of theoretical treatments and simulations. The results are remarkable in several aspects. Not only is it found that the intrinsic properties of P pili are composed in an optimal combination to promote strong multipili bindings. The properties of the pili structure itself are also found to be optimized with respect to its in vivo environment. Indeed, the true meaning of the attributes derived at a single–pilus level cannot be unraveled until a multipili–binding system is considered. Whereas detailed studies are presented for the helix–like P pili expressed by Gram–negative Escherichia coli, conceptual studies are presented for the open coil–like T4 pili expressed by Gram–positive Streptococcus pneumoniae. The structural and adhesive properties of these two types of pili differ considerably. These dissimilarities have far–reaching consequences on the adhesion possibilities at both single–pilus and multipili levels which are discussed qualitatively. Moreover, error analyses of conventional data processing methods in dynamic force spectroscopy as well as development of novel analysis methods are presented. These findings provide better understanding of how to perform refined force measurements on single adhesion organelles as well as how to improve the analyses of measurement data to obtain accurate parameter values of biomechanical entities. In conclusion, this thesis comprises a study of bacterial adhesion organelles and the way they cooperate to establish efficient attachment systems that can successfully withstand strong external forces that acts upon bacteria. Such systems can resist, for instance, rinsing effects and thereby allow bacteria to colonize their host. By understanding the complexity, and thereby possible weaknesses, of bacterial attachments, new targets for combating bacterial infections can be identified.
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| 37. |
- Björnham, Oscar, 1976-, et al.
(author)
-
Catch-Bond behavior of bacteria binding by slip bonds
- 2010
-
In: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 99:5, s. 1331-1341
-
Journal article (peer-reviewed)abstract
- It is shown that multipili-adhering bacteria expressing helix-like pili binding by slip bonds can show catch-bond behavior. When exposed to an external force, such bacteria can mediate adhesion to their hosts by either of two limiting means: sequential or simultaneous pili force exposure (referring to when the pili mediate force in a sequential or simultaneous manner, respectively). As the force is increased, the pili can transition from sequential to simultaneous pili force exposure. Since the latter mode of adhesion gives rise to a significantly longer bacterial adhesion lifetime than the former, this results in a prolongation of the lifetime, which shows up as a catch-bond behavior. The properties and conditions of this effect were theoretically investigated and assessed in some detail for dual-pili-adhering bacteria, by both analytical means and simulations. The results indicate that the adhesion lifetime of such bacteria can be prolonged by more than an order of magnitude. This implies that the adhesion properties of multibinding systems cannot be directly conveyed to the individual adhesion-receptor bonds.
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| 38. |
- Björnham, Oscar, 1976-, et al.
(author)
-
Measurements of the binding force between the Helicobacter pylori adhesin BabA and the Lewis b blood group antigen using optical tweezers
- 2005
-
In: Journal of Biomedical Optics. - Bellingham, WA : SPIE-Intl Soc Optical Eng. - 1083-3668 .- 1560-2281. ; 10:4, s. 044024-044032
-
Journal article (peer-reviewed)abstract
- Helicobacter pylori is a world-wide spread bacterium that causes persistent infections and chronic inflammations that can develop into gastritis and peptic ulcer disease. It expresses several adhesin proteins on its surface that bind to specific receptors in the gastric epithelium. The most well-known adhesin is BabA, which has previously been shown to bind specifically to the fucosylated blood group antigen Lewis b (Leb). The adhesion forces between BabA and the Leb antigen are investigated in this work and assessed by means of optical tweezers. A model system for in situ measurements of the interaction forces between individual bacteria and beads coated with Leb is developed. It is found that the de-adhesion force in this model system, measured with a loading rate of ~100 pN/s, ranges from 20 to 200 pN. The de-adhesion force appears predominantly as multiples of an elementary force, which is determined to 25±1.5 pN and identified as the unbinding force of an individual BabA-Leb binding. It is concluded that adhesion in general is mediated by a small number of bindings (most often 1 to 4) despite that the contact surface between the bacterium and the bead encompassed significantly more binding sites.
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| 39. |
- Björnham, Oscar, 1976-, et al.
(author)
-
Modeling of the elongation and retraction of Escherichia coli P pili under strain by Monte Carlo simulations
- 2008
-
In: European Biophysics Journal. - : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 37:4, s. 381-391
-
Journal article (peer-reviewed)abstract
- P pili are fimbrial adhesion organelles expressed by uropathogenic Escherichia coli in the upper urinary tract. They constitute a stiff helix-like polymer consisting of a number of subunits joined by head-to-tail bonds. The elongation and retraction properties of individual P pili exposed to strain have been modeled by Monte Carlo (MC) simulations. The simulation model is based upon a three-state energy landscape that deforms under an applied force. Bond opening and closure are modeled by Bells theory while the elongation of the linearized part of the pilus is described by a worm-like chain model. The simulations are compared with measurements made by force measuring optical tweezers. It was found that the simulations can reproduce pili elongation as well as retraction, under both equilibrium and dynamic conditions, including entropic effects. It is shown that the simulations allow for an assessment of various model parameters, e.g. the unfolding force, energy barrier heights, and various distances in the energy landscape, including their stochastic spread that analytical models are unable to do. The results demonstrate that MC simulations are useful to model elongation and retraction properties of P pili, and therefore presumably also other types of pili, exposed to strain and/or stress. MC simulations are particularly suited for description of helix-like pili since these have an intricate self-regulating mechanical elongation behavior that makes analytical descriptions non-trivial when dynamic processes are studied, or if additional interactions in the rod or the behavior of the adhesion tip needs to be modeled.
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| 40. |
- Björnham, Oscar, 1976-, et al.
(author)
-
Multipili Attachment of Bacteria with Helix–like Pili Exposed to Stress
- 2009
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130, s. 235102-
-
Journal article (peer-reviewed)abstract
- A number of biomechanical properties of various types of pili expressed by Escherichia coli, predominantly their force–vs.–elongation behavior, have previously been assessed in detail on a single pilus level. In vivo, however, bacteria bind in general to host cells by a multitude of pili, which presumably provides them with adhesion properties that differs from those of single pili. Based upon the previously assessed biomechanical properties of individual pili, this work presents a theoretical analysis of the adhesion properties of multipili–attaching bacteria expressing helix–like pili exposed to an external force. Expressions for the adhesion lifetime of dual– and multipili–attaching bacteria are derived and their validity is verified by Monte Carlo simulations. It is shown that the adhesion lifetime of a multipili–binding bacterium depends to a large degree on the cooperativity of the attaching pili, which, in turn, depends strongly on their internal biomechanical properties, in particular their helix–like structure and its ability to elongate, which, in turn, depend on the intrinsic properties of the bonds, e.g. their lengths and activation energies. It is shown, for example, that a decrease in the length of a layer–to–layer bond in the rod of P pili, expressed by E. coli, by 50 % leads to a decrease in the adhesion lifetime of a bacterium attaching by 10 pili and exposed to a force of 500 pN by three orders of magnitude. The results indicate moreover that the intrinsic properties of the rod for this particular type of pili are optimized for multipili attachment under a broad range of external forces and presumably also to its in vivo environment. Even though the results presented in this work apply quantitatively to one type of pilus, they are assumed to apply qualitatively to all helix–like pili systems expressing slip bonds.
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| 41. |
- Boudreau, Denis, et al.
(author)
-
DensMat: fully time-resolved simulation of two-step pulsed laser excitation of atoms in highly collisional media
- 1996
-
In: Spectrochimica Acta Part B - Atomic Spectroscopy. - : Elsevier. - 0584-8547 .- 1873-3565. ; 51:4, s. 413-428
-
Journal article (peer-reviewed)abstract
- A program that simulates and displays the level populations of atomic systems exposed to dual-wavelength (i.e. two-colour) pulsed laser excitation in highly collisional media (such as flames and plasmas) has been developed. The program is based upon a previously published fully time-dependent density-matrix model that describes step-wise excitations of atoms with degenerate states under collision-dominated conditions, and which thus goes beyond the rate-equations formalism. This model can predict such phenomena as Rabi flopping and a.c.-Stark splitting, shifting and broadening. The program can be used as a prediction tool for laser-enhanced ionization, laser-induced fluorescence, fluorescence dip spectroscopy and other two-colour laser-based spectroscopic experiments. The program provides the user with a flexible four-level atomic system, configurable as a one- or two-step excitation ladder, along with an ionization continuum and non-laser-connected level(s) that may act as trap(s) or metastable level(s). Parameters such as level degeneracy, collisional rates and laser pulse widths, shapes, wavelengths, intensities and bandwidths are accessible to the user. The program can display both the time development of the level populations and also level populations versus laser wavelength. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by a disk containing the program DensMat, an associated on-line help file and manual, an installation program, and data files pertaining to the examples illustrated in this article. The program runs under Windows 3.1 on an IBM-compatible computer.
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| 42. |
- Boudreau, Denis, et al.
(author)
-
The use of DensMat to model stimulated Raman adiabatic passage processes in atoms
- 2001
-
In: Spectrochimica Acta Part B - Atomic Spectroscopy. - : Elsevier. - 0584-8547 .- 1873-3565. ; 56:9, s. 1787-1795
-
Journal article (peer-reviewed)abstract
- Stimulated Raman Adiabatic Passage (STIRAP) is a technique that is capable of transferring an almost entire atomic or molecular population from one quantum level to another by a coherent two-step excitation process. The most remarkable property of this technique is that it is applicable to situations in which the intermediate atomic or molecular state is exposed to a large loss rate. However, the STIRAP process has not yet been used for laser spectrochemical analysis. As a part of the ongoing development of new laser-based spectrometric techniques, this article demonstrates how a previously published simulation program, DensMat, can be used to model STIRAP processes in atoms under various collisional and laser bandwidth conditions.
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| 43. |
- Broström, Markus, et al.
(author)
-
IACM - In situ alkali chloride monitor
- 2004
-
In: 2nd World Conference for Energy, Industry and Climate Protection, Rome, Italy.
-
Conference paper (other academic/artistic)
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| 44. |
- Castelain, Mickaël, et al.
(author)
-
Characterization of the Biomechanical Properties of T4 Pili Expressed by Streptococcus pneumoniae – A Comparison between Helix-like and Open Coil-like Pili
- 2009
-
In: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 10:9-10, s. 1533-1540
-
Journal article (peer-reviewed)abstract
- Bacterial adhesion organelles, known as fimbria or pili, are expressed by Gram–positive as well as Gram–negative bacteria families. These appendages play a key role in the first steps of the invasion and infection processes, and they therefore provide bacteria with pathogenic abilities. To improve the knowledge of pili-mediated bacterial adhesion to host cells and how these pili behave under the presence of an external force, we first characterize, using force measuring optical tweezers, open coil-like T4 pili expressed by Gram–positive Streptococcus pneumoniae with respect to their biomechanicalproperties. It is shown that their elongation behavior can be well described by the worm-like chain model and that they possess a large degree of flexibility. Their properties are then compared with those of helix-like pili expressed by Gram–negative uropathogenic Escherichia coli (UPEC), which have different pili architecture. The differences suggest that these two types of pili have distinctly dissimilar mechanisms to adhere and sustain external forces. Helix-like pili expressed by UPEC bacteria adhere to host cells by single adhesins located at the distal end of the pili while their helix-like structures act as shock absorbers to dampen the irregularly shear forces induced by urine flow and to increase the cooperativity of the pili ensemble. Open coil-like pili expressed by S. pneumoniae adhere to cells by a multitude of adhesins distributed along the pili. It is hypothesized that these two types of pili represent different strategies of adhering to host cells in the presence of external forces. When exposed to significant forces, bacteria expressing helix-like pili remain attached bydistributing the external force among a multitude of pili, whereas bacteria expressing open coil-like pili sustain large forces primarily by their multitude of binding adhesins.
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| 45. |
- Castelain, Mickaël, et al.
(author)
-
Fast uncoiling kinetics of F1C pili expressed by uropathogenic Escherichia coli are revealed on a single pilus level using force-measuring optical tweezers
- 2011
-
In: European Biophysics Journal. - : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 40:3, s. 305-316
-
Journal article (peer-reviewed)abstract
- Uropathogenic Escherichia coli (UPEC) expressvarious kinds of organelles, so-called pili or fimbriae, thatmediate adhesion to host tissue in the urinary tract throughspecific receptor-adhesin interactions. The biomechanicalproperties of these pili have been considered important forthe ability of bacteria to withstand shear forces from rinsingurine flows. Force-measuring optical tweezers have beenused to characterize individual organelles of F1C typeexpressed by UPEC bacteria with respect to such properties.Qualitatively, the force-versus-elongation response wasfound to be similar to that of other types of helix-like piliexpressed by UPEC, i.e., type 1, P, and S, with force-inducedelongation in three regions, one of which represents theimportant uncoiling mechanism of the helix-like quaternarystructure. Quantitatively, the steady-state uncoiling forcewas assessed as 26.4 ±1.4 pN, which is similar to those ofother pili (which range from 21 pN for SI to 30 pN for type 1).The corner velocity for dynamic response (1,400 nm/s) wasfound to be larger than those of the other pili (400–700 nm/sfor S and P pili, and 6 nm/s for type 1). The kinetics werefound to be faster, with a thermal opening rate of 17 Hz, afew times higher than S and P pili, and three orders ofmagnitude higher than type 1. These data suggest that F1Cpili are, like P and S pili, evolutionarily selected to primarilywithstand the conditions expressed in the upper urinary tract.
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| 46. |
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| 47. |
- Centeno, R., et al.
(author)
-
External cavity diode laser-based detection of trace gases with NICE-OHMS using current modulation
- 2015
-
In: Optics Express. - 1094-4087. ; 23:5, s. 6277-6282
-
Journal article (peer-reviewed)abstract
- We combine an external cavity diode laser with noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) using current modulation. With a finesse of 1600, we demonstrate noise equivalent absorption sensitivities of 4.1 x 10(-10) cm(-1) Hz(-1/2), resulting in sub-ppbv detection limits for Doppler-broadened transitions of CH4 at 6132.3 cm(-1), C2H2 at 6578.5 cm(-1) and HCN at 6541.7 cm(-1). The system is used for hydrogen cyanide detection from sweet almonds.
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| 48. |
- Chekalin, Nikolai, et al.
(author)
-
Laser-induced fluorescence in graphite furnaces under low pressure conditions as a powerful technique for studies of atomization mechanisms : investigation of Ag
- 1994
-
In: Spectrochimica Acta Part B - Atomic Spectroscopy. - : Elsevier. - 0584-8547 .- 1873-3565. ; 49:12-14, s. 1411-1435
-
Journal article (peer-reviewed)abstract
- A new method for accurate studies of atomization processes of various elements in graphite furnaces has been developed. It utilizes the highly sensitive Laser-Induced Fluorescence spectrometry technique for detection of atoms in Graphite Furnaces under Low Pressure conditions (LIF-GF-LP). The high sensitivity of the LIF technique enables the study of atomization processes at low pressures under true analytical conditions (i.e. for low analyte mass) with a minimum of influences from diffusion processes. This first work is concerned with an investigation of the atomization mechanisms of Ag. It was found that the LIF-GF signal area was linear with pressure for virtually all pressures. The LIF-GF signal shape (versus time as well as versus 1/T) was found to vary with both pressure and concentration. The signals were, in general, found to have a shorter duration and higher appearance and peak temperatures, the higher the pressure. Activation energies could be evaluated from the LIF-GF-LP curves very accurately by the Smets method. Excellent agreements with the predicted linear relationship were obtained for a major part of the signal curve (> 50%) under many sample and furnace conditions. Studies of the activation energy dependence on pressure, analyte mass and heating rate gave valuable information about the atomization mechanisms of Ag in graphite furnaces. The findings support a picture that Ag atomizes as individual adatoms under low pressure and low analyte mass conditions. Under atmospheric conditions, repeated desorption and adsorption processes delay the appearance of the signal in time as well as being responsible for formation of 2-D and 3-D microstructures on the surface.
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| 49. |
- Chekalin, N. V., et al.
(author)
-
Investigation of evaporation and atomization processes in a variable-pressure electrothermal atomizer by laser spectroscopy using gallium as an example
- 2000
-
In: Journal of Analytical Chemistry. - : Maik Nauka/Interperiodica. - 1061-9348 .- 1608-3199. ; 55:6, s. 561-566
-
Journal article (peer-reviewed)abstract
- A new approach to studying the evaporation and atomization of elements in graphite furnaces has been developed that combines a highly sensitive technique of laser-induced fluorescence and variable-pressure atomization. This approach allows one to work with low concentrations of analytes corresponding to real analytical conditions, to separate concurrent processes of evaporation and atomization, and to determine their parameters. The approach has been used for studying the evaporation and atomization of gallium in isothermal graphite furnaces.
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| 50. |
- Chekalin, N. V., et al.
(author)
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Studying element vaporization and atomization processes in electrothermal atomizers by laser-excited atomic fluorescence spectrometry: indium, matrix effects
- 2000
-
In: Journal of Analytical Chemistry. - : Maik Nauka/Interperiodica. - 1061-9348 .- 1608-3199. ; 55:10, s. 964-971
-
Journal article (peer-reviewed)abstract
- Indium vaporization and atomization processes were studied in a variable-pressure atomizer by laser-excited fluorescence spectrometry for various analyte masses over a wide range of buffer-gas pressures. It was found that the atomization processes are of intricate nature and depend on the element mass, pressure, and heating rate. Based on the data obtained over a wide range of pressures, individual atomization processes were singled out and their parameters were determined. The effects of KCl and CuCl2 matrices on the kinetics and other characteristics of the processes were investigated. Possible mechanisms of indium vaporization and atomization under various experimental conditions and mechanisms of matrix effects on the analytical signals of indium and gallium are discussed.
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