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  • 1.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Ability of gas modulation to reduce the pickup of drifts in refractometry2021In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 38, no 8, p. 2419-2436Article in journal (Refereed)
    Abstract [en]

    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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  • 2.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Ability of gas modulation to reduce the pickup of fluctuations in refractometry2020In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 37, no 7, p. 1956-1965Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Assessment of gas molar density by gas modulation refractometry: A review of its basic operating principles and extraordinary performance2021In: Spectrochimica Acta Part B - Atomic Spectroscopy, ISSN 0584-8547, E-ISSN 1873-3565, Vol. 179, article id 106121Article, review/survey (Refereed)
    Abstract [en]

    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.

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  • 4.
    Enevold, Jenny
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Realizing large-area arrays of semiconducting fullerene nanostructures with direct laser interference patterning2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 1, p. 540-545Article in journal (Refereed)
  • 5.
    Forssén, Clayton
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Amer, E.
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Szabo, D.
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Bock, T.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Kussicke, A.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Rubin, T.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Mari, D.
    Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy.
    Pasqualin, S.
    Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy.
    Silvestri, Z.
    LNE-Cnam, Paris, France.
    Bentouati, D.
    Laboratoire National de Métrologie et d'Essais, (LNE), Paris, France.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, M.
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Circular comparison of conventional pressure standards using a transportable optical refractometer: preparation and transportation2022In: 6th TC16 Conference on Pressure and Vacuum Measurement 2022, Together with the 24th TC3 Conference on the Measurement of Force, Mass and Torque, the 14th TC5 Conference on the Measurement of Hardness, and the 5th TC22 Conference on Vibration Measurement, International Measurement Confederation (IMEKO) , 2022Conference paper (Refereed)
    Abstract [en]

    Using a transportable Fabry-Pérot cavity refractometer, a circular comparison of existing primary standards at several national metrology institutes is currently underway. This paper provides information about the refractometer, the preparation for the comparison, and the transportation procedure.

  • 6.
    Forssén, Clayton
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Amer, Eynas
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Szabo, David
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Bock, Thomas
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Kussicke, André
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Rubin, Tom
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Mari, Domenico
    Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy.
    Pasqualin, Stefano
    Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy.
    Silvestri, Zaccaria
    Conservatoire national des arts et métiers (CNAM), LNE-CNAM, Paris, France.
    Bentouati, Djilali
    Laboratoire National de Métrologie et d'Essais, (LNE), Paris, France.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Demonstration of a transportable Fabry–Pérot refractometer by a ring-type comparison of dead-weight pressure balances at four European national metrology institutes2024In: Sensors, E-ISSN 1424-8220, Vol. 24, no 1, article id 7Article in journal (Refereed)
    Abstract [en]

    Fabry–Pérot-based refractometry has demonstrated the ability to assess gas pressure with high accuracy and has been prophesized to be able to realize the SI unit for pressure, the pascal, based on quantum calculations of the molar polarizabilities of gases. So far, the technology has mostly been limited to well-controlled laboratories. However, recently, an easy-to-use transportable refractometer has been constructed. Although its performance has previously been assessed under well-controlled laboratory conditions, to assess its ability to serve as an actually transportable system, a ring-type comparison addressing various well-characterized pressure balances in the 10–90 kPa range at several European national metrology institutes is presented in this work. It was found that the transportable refractometer is capable of being transported and swiftly set up to be operational with retained performance in a variety of environments. The system could also verify that the pressure balances used within the ring-type comparison agree with each other. These results constitute an important step toward broadening the application areas of FP-based refractometry technology and bringing it within reach of various types of stakeholders, not least within industry.

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  • 7.
    Forssén, Clayton
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    The short-term performances of two independent gas modulated refractometers for pressure assessments2021In: Sensors, E-ISSN 1424-8220, Vol. 21, no 18, article id 6272Article in journal (Refereed)
    Abstract [en]

    Refractometry is a powerful technique for pressure assessments that, due to the recent redefinition of the SI system, also offers a new route to realizing the SI unit of pressure, the Pascal. Gas modulation refractometry (GAMOR) is a methodology that has demonstrated an outstanding ability to mitigate the influences of drifts and fluctuations, leading to long-term precision in the 10−7 region. However, its short-term performance, which is of importance for a variety of applications, has not yet been scrutinized. To assess this, we investigated the short-term performance (in terms of precision) of two similar, but independent, dual Fabry–Perot cavity refractometers utilizing the GAMOR methodology. Both systems assessed the same pressure produced by a dead weight piston gauge. That way, their short-term responses were assessed without being compromised by any pressure fluctuations produced by the piston gauge or the gas delivery system. We found that the two refractometer systems have a significantly higher degree of concordance (in the 10−8 range at 1 s) than what either of them has with the piston gauge. This shows that the refractometry systems under scrutiny are capable of assessing rapidly varying pressures (with bandwidths up to 2 Hz) with precision in the 10−8 range.

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  • 8.
    Forssén, Clayton
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, Rise Research Institutes of Sweden, Borås, Sweden.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, M.
    Measurement Science and Technology, Rise Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    An optical pascal in Sweden2022In: Journal of Optics, ISSN 2040-8978, E-ISSN 2040-8986, Vol. 24, no 3, article id 033002Article, review/survey (Refereed)
    Abstract [en]

    By measuring the refractivity and the temperature of a gas, its pressure can be assessed from fundamental principles. The highest performing instruments are based on Fabry-Perot cavities where a laser is used to probe the frequency of a cavity mode, which is shifted in relation to the refractivity of the gas in the cavity. Recent activities have indicated that such systems can demonstrate an extended uncertainty in the 10 ppm (parts-per-million or 10-6) range. As a means to reduce the influence of various types of disturbances (primarily drifts and fluctuations) a methodology based on modulation, denoted gas modulation refractometry (GAMOR), has recently been developed. Systems based on this methodology are in general high-performance, e.g. they have demonstrated precision in the sub-ppm range, and they are sturdy. They can also be made autonomous, allowing for automated and unattended operation for virtually infinite periods of time. To a large degree, the development of such instruments depends on the access to modern photonic components, e.g. narrow line-width lasers, electro-and acousto-optic components, and various types of fiber components. This work highlights the role of such modern devices in GAMOR-based instrumentation and provides a review on the recent development of such instruments in Sweden that has been carried out in a close collaboration between a research institute and the Academy. It is shown that the use of state-of-the-art photonic devices allows sturdy, automated and miniaturized instrumentation that, for the benefit of industry, can serve as standards for pressure and provide fast, unattended, and calibration-free pressure assessments at a fraction of the present cost.

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  • 9.
    Forssén, Clayton
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, M.
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fabry-Perot-cavity-based refractometry without influence of mirror penetration depth2021In: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, ISSN 2166-2746, E-ISSN 2166-2754, Vol. 39, no 6, article id 065001Article in journal (Refereed)
    Abstract [en]

    Assessments of refractivity in a Fabry-Perot (FP) cavity by refractometry often encompass a step in which the penetration depth of the light into the mirrors is estimated to correct for the fraction of the cavity length into which no gas can penetrate. However, as it is currently carried out, this procedure is not always coherently performed. Here, we discuss a common pitfall that can be a reason for this and provide a recipe on how to perform FP-cavity-based refractometry without any influence of mirror penetration depth.

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  • 10.
    Mortezaei, Narges
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Singh, Bhupender
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bullitt, Esther
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Epler, Chelsea
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Structural and biophysical comparison of UPEC and ETEC adhesion fimbriae2015In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 108, no 2, suppl 1, p. 527A-527AArticle in journal (Refereed)
    Abstract [en]

    Adhesion fimbriae (pili) of uropathogenic and enterotoxigenic Escherichia coli (UPEC and ETEC, respectively) facilitate adherence of the bacteria to target cells. Fimbriae are absolutely necessary for colonization and biofilm formation in the initiation of disease. The types of fimbriae expressed on the bacterial surface vary with the preferred environmental niche of the bacterial strain. For example, UPEC that express P-pili are most frequently associated pyelonephritis, an infection in the upper urinary tract, whereas bacteria that express type 1 fimbriae commonly cause cystitis through infection of the lower urinary tract. In contrast, ETEC expressing CFA/I and CS2 pili are associated with diarrheal diseases, initiating disease in the small intestines.

    Although expressed in different enviroments, these fimbriae share basic structural and biomechanical features. Structurally, they are all long (1-4 μm), thin (7-8 nm diameter) helix-like filaments that extend from the bacterial surface. Biomechanically, they share the ability to be extended into a thinner filament (2-3 nm diameter) by unwinding of the helical filament under a constant force. However, the force required to unwind is specific to each fimbrial type. In addition, the dependence of the force required to unwind a fimbria on the velocity of this unwinding, (that is, the kinetics of unwinding), is also type-specific and highly variable. These biomechanical parameters are dissimilar for UPEC and ETEC expressed fimbriae, separating them into two distinct groups. Using force spectroscopy data, helical reconstructions from electron microscopy data, and computational simulations, we show in this work how these pronounced biomechanical differences may be beneficial for bacterial survival in a given environment.

  • 11.
    Mortezaei, Narges
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Singh, Bhupender
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bullitt, Esther
    Boston University School of Medicine, Boston, Massachusetts, USA.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Biomechanical and Structural features of CS2 fimbriae of Enterotoxigenic Escherichia coli 2015In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 109, no 1, p. 49-56Article in journal (Refereed)
    Abstract [en]

    Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrhea worldwide, and infection of children in underdeveloped countries often leads to high mortality rates. Isolated ETEC express a plethora of colonization factors (fimbriae/pili), of which CFA/I and CFA/II that are assembled via the alternate chaperone pathway (ACP), are amongst the most common. Fimbriae are filamentous structures, whose shafts are primarily composed of helically arranged single pilin-protein subunits, with a unique biomechanical capability allowing them to unwind and rewind. A sustained ETEC infection, under adverse conditions of dynamic shear forces, is primarily attributed to this biomechanical feature of ETEC fimbriae. Recent understandings about the role of fimbriae as virulence factors are pointing to an evolutionary adaptation of their structural and biomechanical features. In this work, we investigated the biophysical properties of CS2 fimbriae from the CFA/II group. Homology modelling its major structural subunit CotA reveals structural clues and these are related to the niche in which they are expressed. Using optical tweezers force spectroscopy we found that CS2 fimbriae unwind at a constant force of 10 pN and have a corner velocity of 1300 nm/s, i.e., the velocity at which the force required for unwinding rises exponentially with increased speed. The biophysical properties of CS2 fimbriae assessed in this work classify them into a low-force unwinding group of fimbriae together with the CFA/I and CS20 fimbriae expressed by ETEC strains. The three fimbriae are expressed by ETEC, colonize in similar gut environments, and exhibit similar biophysical features, but differ in their biogenesis. Our observation suggests that the environment has a strong impact on the biophysical characteristics of fimbriae expressed by ETEC.

  • 12.
    Rubin, T.
    et al.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Amer, E.
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Szabo, D.
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Bock, T.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Kussicke, A.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Günz, C.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Mari, D.
    Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy.
    Gavioso, R.M.
    Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy.
    Pisani, M.
    Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy.
    Ripa, D. Madonna
    Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy.
    Silvestri, Z.
    Laboratoire National de Métrologie et d'Essais (LNE), Conservatoire National des Arts et Métiers (CNAM), Paris, France.
    Gambette, P.
    Laboratoire National de Métrologie et d'Essais (LNE), Conservatoire National des Arts et Métiers (CNAM), Paris, France.
    Bentouati, D.
    Laboratoire National de Métrologie et d'Essais (LNE), Conservatoire National des Arts et Métiers (CNAM), Paris, France.
    Garberoglio, G.
    European Centre for Theoretical Studies in Nuclear Physics and Related Areas (FBK-ECT*), Trento Institute for Fundamental Physics and Applications (TIFPA-INFN), Trento, Italy.
    Lesiuk, M.
    Faculty of Chemistry, University of Warsaw and Pasteura 1, Warsaw, Poland.
    Przybytek, M.
    Faculty of Chemistry, University of Warsaw and Pasteura 1, Warsaw, Poland.
    Jeziorski, B.
    Faculty of Chemistry, University of Warsaw and Pasteura 1, Warsaw, Poland.
    Setina, J.
    IMT Institute of Metals and Technology, Lepi Pot, Ljubljana, Slovenia.
    Zelan, M.
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    'Quantum-based realizations of the pascal' status and progress of the empir-project: quantumpascal2022In: 6th TC16 Conference on Pressure and Vacuum Measurement 2022, Together with the 24th TC3 Conference on the Measurement of Force, Mass and Torque, the 14th TC5 Conference on the Measurement of Hardness, and the 5th TC22 Conference on Vibration Measurement, International Measurement Confederation (IMEKO) , 2022Conference paper (Refereed)
    Abstract [en]

    The QuantumPascal (QP) project combines the capabilities of 12 European institutions to enable traceable pressure measurements utilizing quantum-based methods that evaluate the number density instead of force per area to target the wide pressure range between 1 Pa and 3 MPa. This article summarizes the goals and results since the project start in June 2019.

  • 13.
    Rubin, T.
    et al.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hao, M.
    School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Asbahr, P.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Bernien, M.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Kussicke, A.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Liu, K.
    School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China.
    Zelan, M.
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thermodynamic effects in a gas modulated Invar-based dual Fabry-Pérot cavity refractometer2022In: Metrologia, ISSN 0026-1394, E-ISSN 1681-7575, Vol. 59, no 3, article id 035003Article in journal (Refereed)
    Abstract [en]

    By measuring the refractivity and the temperature of a gas, its pressure can be assessed from fundamental principles. The highest performing instruments are based on Fabry-Perot cavities (FPC). Gas modulation refractometry (GAMOR) is a methodology that has the ability to reduce the influence of disturbances to such an extent that high-precision (sub-parts-per-million) assessments of pressure can be made by the use of FPCs of Invar. To allow for high accuracy assessments, it is of importance to assess the uncertainty contribution from the thermodynamic effects that are associated with the gas filling and emptying of the cavity (pV-work). This paper presents a detailed scrutiny of the influence of the gas exchange process on the assessment of gas temperature on an Invar-based dual-FPC (DFPC) instrumentation. It is shown that by virtue of a combination of a number of carefully selected design entities (a small cavity volume with a bore radius of 3 mm, a spacer material with high heat capacitance, large thermal conductivity, and no regions that are connected with low thermal conductance, i.e. no heat islands, and a continuous assessment of temperature of the cavity spacer) the system is not significantly affected by pV-work. Simulations show that 10 s after the filling all temperature gradients in the system are well into the sub-mK range. Experiments support that refractivity assessments initiated after 40 s are not significantly affected by the pV-work. The analysis given in this work indicates that an upper limit for the influence of pV-work on the Invar-based DFPC system using 100 s long gas modulation cycles is 0.5 mK/100 kPa (or 1.8 ppm/100 kPa). Consequently, thermodynamic effects will not be a limiting factor when the Invar-based DFPC GAMOR system is used for assessments of pressure or as a primary pressure standard up to atmospheric pressures.

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  • 14.
    Rubin, T.
    et al.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hao, M.
    School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Asbahr, P.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Bernien, M.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Kussicke, A.
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Liu, K.
    School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China.
    Zelan, M.
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thermodynamic effects in a gas modulated Invar-based dual Fabry-Pérot cavity refractometer addressing 100 kpa of nitrogen2022In: 6th TC16 Conference on Pressure and Vacuum Measurement 2022, Together with the 24th TC3 Conference on the Measurement of Force, Mass and Torque, the 14th TC5 Conference on the Measurement of Hardness, and the 5th TC22 Conference on Vibration Measurement, International Measurement Confederation (IMEKO) , 2022Conference paper (Refereed)
    Abstract [en]

    An Invar-based dual Fabry-Pérot cavity refractometer used for assessments of pressure by the gas modulation refractometry (GAMOR) methodology has been scrutinized with respect to the influence of thermodynamic effects (pV-work) that originates from the gas exchange process when 100 kPa of nitrogen is addressed. It is shown that the actual temperature variation of the cavity spacer solely is a fraction of the previously assessed upper limits (0.5 mK/100 kPa), limited to sub-parts-per-million (ppm) levels. This finding additionally supports the conclusion that the thermodynamic effects will not be a limiting factor when the system is used for assessments of pressure.

  • 15.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Measurement Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    An invar-based fabry-perot cavity refractometer with a gallium fixed-point cell for assessment of pressure2020In: Acta IMEKO, ISSN 0237-028X, Vol. 9, no 5, p. 293-298Article in journal (Refereed)
    Abstract [en]

    An Invar-based Fabry-Perot cavity refractometer equipped with an automated, miniaturized gallium fixed-point cell for assessment of pressure is presented. The use of an Invar cavity spacer has previously demonstrated pressure assessments with sub-0.1 ppm precision. The fixed-point cell, whose design and implementation are presented here, provides a reference for temperature assessment of the gas inside the cavity with an uncertainty of 4 ppm. This opens up for a self-contained system for realization of the Pascal with an accuracy in the low ppm range. This is an important step towards disseminating the Pascal through fundamental principles.

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  • 16.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Invar-based refractometer for pressure assessments2020In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 45, no 9, p. 2652-2655Article in journal (Refereed)
    Abstract [en]

    Gas modulation refractometry (GAMOR) is a methodology that can mitigate fluctuations and drifts in refractometry. This can open up for the use of non-conventional cavity spacer materials. In this paper, we report a dual-cavity system based on Invar that shows better precision for assessment of pressure than a similar system based on Zerodur. This refractometer shows for empty cavity measurements, up to 10(4) s, a white noise response (for N-2) of 3 mPa s(1/2). At 4303 Pa, the system has a minimum Allan deviation of 0.34 mPa (0.08 ppm) and a long-term stability (24 h) of 0.7 mPa. This shows that the GAMOR methodology allows for the use of alternative cavity materials.

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  • 17.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Optical realization of the pascal—Characterization of two gas modulated refractometers2021In: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, ISSN 2166-2746, E-ISSN 2166-2754, Vol. 39, no 4, article id 044201Article in journal (Refereed)
    Abstract [en]

    By measuring the refractivity and the temperature of a gas, its pressure can be calculated from fundamental principles. The most sensitive instruments are currently based on Fabry-Perot cavities where a laser is used to probe the frequency of a cavity mode. However, for best accuracy, the realization of such systems requires exceptional mechanical stability. Gas modulation refractometry (GAMOR) has previously demonstrated an impressive ability to mitigate the influence of fluctuations and drifts whereby it can provide high-precision (sub-ppm, i.e., sub-parts-per-million or sub-) assessment of gas refractivity and pressure. In this work, two independent GAMOR-based refractometers are individually characterized, compared to each other, and finally compared to a calibrated dead weight piston gauge with respect to their abilities to assess pressure in the 4-25 kPa range. The first system, referred to as the stationary optical pascal (SOP), uses a miniature fixed point gallium cell to measure the temperature. The second system, denoted the transportable optical pascal (TOP), relies on calibrated Pt-100 sensors. The expanded uncertainty for assessment of pressure () was estimated to, for the SOP and TOP, and , respectively. While the uncertainty of the SOP is mainly limited by the uncertainty in the molar polarizability of nitrogen (8 ppm), the uncertainty of the TOP is dominated by the temperature assessment (26 ppm). To verify the long-term stability, the systems were compared to each other over a period of 5 months. It was found that all measurements fell within the estimated expanded uncertainty () for comparative measurements (27 ppm). This verified that the estimated error budget for the uncorrelated errors holds over this extensive period of time.

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  • 18.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silva de Oliveira, Vinicius
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rubin, Tom
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Zelan, Martin
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    In situ determination of the penetration depth of mirrors in Fabry-Perot refractometers and its influence on assessment of refractivity and pressure2022In: Optics Express, E-ISSN 1094-4087, Vol. 30, no 14, p. 25891-25906Article in journal (Refereed)
    Abstract [en]

    A procedure is presented for in situ determination of the frequency penetration depth of coated mirrors in Fabry-Perot (FP) based refractometers and its influence on the assessment of refractivity and pressure. It is based on assessments of the absolute frequency of the laser and the free spectral range of the cavity. The procedure is demonstrated on an Invar-based FP cavity system with high-reflection mirrors working at 1.55 µm. The influence was assessed with such a low uncertainty that it does not significantly contribute to the uncertainties (k = 2) in the assessment of refractivity (<8 × 10−13) or pressure of nitrogen (<0.3 mPa).

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  • 19.
    Stangner, Tim
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dahlberg, Tobias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Svenmarker, Pontus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Oddershede, Lene B.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cooke-Triplet-Tweezers: More compact, robust and efficient optical tweezers2018In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 43, no 9, p. 1990-1993Article in journal (Refereed)
    Abstract [en]

    We present a versatile three-lens optical design to improve the overall compactness, efficiency, and robustness for optical tweezers based applications. The design, inspired by the Cooke–Triplet configuration, allows for continuous beam magnifications of 2–10× , and axial as well as lateral focal shifts can be realized without switching lenses or introducing optical aberrations. We quantify the beam quality and trapping stiffness and compare the Cooke–Triplet design with the commonly used double Kepler design through simulations and direct experiments. Optical trapping of 1 and 2 μm beads shows that the Cooke–Triplet possesses an equally strong optical trap stiffness compared to the double Kepler lens design but reduces its lens system length by a factor of 2.6. Finally, we demonstrate how a Twyman–Green interferometer integrated in the Cooke–Triplet optical tweezers setup provides a fast and simple method to characterize the wavefront aberrations in the lens system and how it can help in aligning the optical components perfectly.

  • 20.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    The mechanics of adhesion polymers and their role in bacterial attachment2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Bacterial resistance to antibiotics is increasing at a high rate in both developing and developed countries. To circumvent the problem of drug-resistant bacterial pathogens, we need to develop new effective methods, substances, and materials that can disarm and prevent them from causing infections. However, to do this we first need to find new possible targets in bacteria to approach and novel strategies to apply.Escherichia coli (E. coli) bacteria is a normal member of the intestinal microflora of humans and mammals, but frequently cause diverse intestinal and external diseases by means of virulence factors, which leads to hundreds of million sick people each year with a high mortality rate. An E. coli bacterial infection starts with adhesion to a host cell using cell surface expressed adhesion polymers, called adhesion pili. Depending on the local environment different types of pili are expressed by the bacteria. For example, bacteria found in the gastrointestinal tract commonly express different pili in comparison to those found in the urinary tract and respiratory tract. These pili, which are vital for bacterial adhesion, thereby serve as a new possible approach in the fight against bacterial infections by targeting and disabling these structures using novel chemicals. However, in order to develop such chemicals, better understanding of these pili is needed.Optical tweezers (OT) can measure and apply forces up to a few hundred pN with sub-pN force resolution and have shown to be an excellent tool for investigating mechanical properties of adhesion pili. It has been found that pili expressed by E. coli have a unique and complex force-extension response that is assumed to be important for the ability of bacteria to initiate and maintain attachment to the host cells. However, their mechanical functions and the advantage of specific mechanical functions, especially in the initial attachment process, have not yet been fully understood.In this work, a detailed description of the pili mechanics and their role during cell adhesion is presented. By using results from optical tweezers force spectroscopy experiments in combination with physical modeling and numerical simulations, we investigated how pili can act as “shock absorbers” through uncoiling and thereby lower the fluid force acting on a bacterium. Our result demonstrate that the dynamic uncoiling capability of the helical part of the adhesion pili modulate the force to fit the optimal lifetime of its adhesin (the protein that binds to the receptor on the host cell), ensuring a high survival probability of the bond.iiiSince the attachment process is in proximity of a surface we also investigated the influence of tether properties and the importance of different surface corrections and additional force components to the Stokes drag force during simulations. The investigation showed that the surface corrections to the Stokes drag force and the Basset force cannot be neglected when simulating survival probability of a bond, since that can overestimate the probability by more than an order of magnitude.Finally, a theoretical and experimental framework for two separate methods was developed. The first method can detect the presence of pili on single cells using optical tweezers. We verified the method using silica microspheres coated with a polymer brush and E. coli bacteria expressing; no pili, P pili, and type 1 pili, respectively. The second method was based on digital holography microscopy. Using the diffraction of semi-transparent object such as red blood cells, we showed that this method can reconstruct the axial position and detect morphological changes of cells.

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    The mechanics of adhesion polymers and their role in bacterial attachment
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  • 21.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cell shape identification using digital holographic microscopy2015In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 54, no 24, p. 7442-7448Article in journal (Refereed)
    Abstract [en]

    We present a cost-effective, simple and fast digital holographic microscopy method based upon Rayleigh-Sommerfeld back propagation for identification of the geometrical shape of a cell. The method was tested using synthetic hologram images generated by ray-tracing software and from experimental images of semi-transparent spherical beads and living red blood cells. Our results show that by only using the real part of the back-reconstructed amplitude the proposed method can provide information of the geometrical shape of the object and at the same time accurately determine the axial position of the object under study. The proposed method can be used in flow chamber assays for pathophysiological studies where fast morphological changes of cells are studied in high numbers and at different heights.

  • 22.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silvestri, Zaccaria
    LNE-Cnam, 61 rue du Landy, La Plaine Saint-Denis, France.
    Mari, D.
    INRiM, National Institute of Metrological Research, Strada delle cacce, 91, Torino, Italy.
    Pasqualin, S.
    INRiM, National Institute of Metrological Research, Strada delle cacce, 91, Torino, Italy.
    Kussicke, Andre
    Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, Berlin, Germany.
    Asbahr, Patrick
    Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, Berlin, Germany.
    Rubin, Tom
    Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, Berlin, Germany.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Simulation of pressure-induced cavity deformation: the 18SIB04 Quantumpascal EMPIR project2020In: Acta IMEKO, ISSN 0237-028X, Vol. 9, no 5, p. 281-286Article in journal (Refereed)
    Abstract [en]

    The 18SIB04 QuantumPascal EMPIR project aims for development of photon-based standards that can replace primary standards of the SI unit of pressure, the Pascal. In this project, four partners simulated the pressure-induced deformation of a given Fabry-Pérot cavity, using various versions of two types of software, COMSOL Multiphysics® and ANSYS Workbench. It was demonstrated that, for a given geometry and set of material parameters, simulations of the deformation could be performed by the various partners with such small discrepancies that methodological mistakes of the simulation procedures will solely contribute to a sub-ppm uncertainty in the assessments of refractivity of N2.

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  • 23.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Zelan, Martin
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Procedure for robust assessment of cavity deformation in Fabry-Perot based refractometers2020In: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, ISSN 2166-2746, E-ISSN 2166-2754, Vol. 38, no 5, article id 054202Article in journal (Refereed)
    Abstract [en]

    A novel procedure for a robust assessment of cavity deformation in Fabry-Perot (FP) refractometers is presented. It is based on scrutinizing the difference between two pressures: one assessed by the uncharacterized refractometer and the other provided by an external pressure reference system, at a series of set pressures for two gases with dissimilar refractivity (here, He and N2). By fitting linear functions to these responses and extracting their slopes, it is possible to construct two physical entities of importance: one representing the cavity deformation and the other comprising a combination of the systematic errors of a multitude of physical entities, viz., those of the assessed temperature, the assessed or estimated penetration depth of the mirror, the molar polarizabilities, and the set pressure. This provides a robust assessment of cavity deformation with small amounts of uncertainties. A thorough mathematical description of the procedure is presented that serves as a basis for the evaluation of the basic properties and features of the procedure. The analysis indicates that the cavity deformation assessments are independent of systematic errors in both the reference pressure and the assessment of gas temperature and when the gas modulation refractometry methodology is used that they are insensitive to gas leakages and outgassing into the system. It also shows that when a high-precision (sub-ppm) refractometer is characterized according to the procedure, when high purity gases are used, the uncertainty in the deformation contributes to the uncertainty in the assessment of pressure of N-2 with solely a fraction (13%) of the uncertainty of its molar polarizability, presently to a level of a few ppm. This implies, in practice, that cavity deformation is no longer a limiting factor in FP-based refractometer assessments of pressure of N-2.

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  • 24.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silva de Oliveira, Vinicius
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hjältén, Adrian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rosina, Andrea
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rubin, Tom
    Physikalisch-Technische Bundesanstalt (PTB), Abbestr 2-12, Berlin, Germany.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Procedure for automated low uncertainty assessment of empty cavity mode frequencies in Fabry-Pérot cavity based refractometry2024In: Optics Express, E-ISSN 1094-4087, Vol. 32, no 3, p. 3959-3973Article in journal (Refereed)
    Abstract [en]

    A procedure for automated low uncertainty assessment of empty cavity mode frequencies in Fabry-Pérot cavity based refractometry that does not require access to laser frequency measuring instrumentation is presented. It requires a previously well-characterized system regarding mirror phase shifts, Gouy phase, and mode number, and is based on the fact that the assessed refractivity should not change when mode jumps take place. It is demonstrated that the procedure is capable of assessing mode frequencies with an uncertainty of 30 MHz, which, when assessing pressure of nitrogen, corresponds to an uncertainty of 0.3 mPa.

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  • 25.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Singh, Bhupender
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Svenmarker, Pontus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hakobyan, Shoghik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Detecting the presence of surface organelles at the single cell level, a novel cell sorting approachManuscript (preprint) (Other academic)
  • 26.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Singh, Bhupender
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Svenmarker, Pontus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhang, Hanqing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hakobyan, Shoghik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Detecting Bacterial Surface Organelles on Single Cells using Optical Tweezers2016In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 18, p. 4521-4529Article in journal (Refereed)
    Abstract [en]

    Bacterial cells display a diverse array of surface organelles that are important for a range of processes such as: intercellular communication, motility and adhesion leading to biofilm formation, infections and bacterial spread. More specifically, attachment to host cells by Gram-negative bacteria are mediated by adhesion pili, which are nm wide and µm long fibrous organelles. Since these pili are significantly thinner than the wavelength of visible light, they cannot be detected using standard light microscopy techniques. At present, there is no fast and simple method available to investigate if a single cell expresses pili while keeping the cell alive for further studies. In this study, we present a method to determine the presence of pili on a single bacterium. The protocol involves imaging the bacterium to measure its size, followed by predicting the fluid drag based on its size using an analytical model, and thereafter oscillating the sample while a single bacterium is trapped by an optical tweezer to measure its effective fluid drag. Comparison between the predicted and the measured fluid drag thereby indicate the presence of pili. Herein, we verify the method using polymer coated silica microspheres and Escherichia coli bacteria expressing adhesion pili. Our protocol, can in real time and within seconds assist single cell studies by distinguishing between piliated and non-piliated bacteria.

  • 27.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Helix-like bio-polymers can act as effective dampers for bacteria in flows2012In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 41, no 6, p. 551-560Article in journal (Refereed)
    Abstract [en]

    Biopolymers are vital structures for many liv- ing organisms; for a variety of bacteria, adhesion polymers play a crucial role for the initiation of colonization. Some bacteria express, on their surface, attachment organelles (pili) that comprise subunits formed into stiff helix-like structures that possess unique biomechanical properties. These helix-like structures possess a high degree of flexi- bility that gives the biopolymers a unique extendibility. This has been considered beneficial for piliated bacteria adhering to host surfaces in the presence of a fluid flow. We show in this work that helix-like pili have the ability to act as efficient dampers of force that can, for a limited time, lower the load on the force-mediating adhesin-receptor bond on the tip of an individual pilus. The model presented is applied to bacteria adhering with a single pilus of either of the two most common types expressed by uropathogenic Escherichia coli, P or type 1 pili, subjected to realistic flows. The results indicate that for moderate flows (~25 mm/s) the force experienced by the adhesin-receptor interaction at the tip of the pilus can be reduced by a factor of ~6 and ~4, respectively. The uncoiling ability pro- vides a bacterium with a ‘‘go with the flow’’ possibility that acts as a damping. It is surmised that this can be an important factor for the initial part of the adhesion process, in particular in turbulent flows, and thereby be of use for bacteria in their striving to survive a natural defense such as fluid rinsing actions.

  • 28.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Tethered cells in fluid flows: beyond the Stokes’ drag force approach2015In: Physical Biology, ISSN 1478-3967, E-ISSN 1478-3975, Vol. 12, article id 056006Article in journal (Refereed)
    Abstract [en]

    Simulations of tethered cells in viscous sub-layers are frequently performed using the Stokes' drag force, but without taking into account contributions from surface corrections, lift forces, buoyancy, the Basset force, the cells' finite inertia, or added mass. In this work, we investigate to what extent such contributions, under a variety of hydrodynamic conditions, influence the force at the anchor point of a tethered cell and the survival probability of a bacterium that is attached to a host by either a slip or a catch bond via a tether with a few different biomechanical properties. We show that a consequence of not including some of these contributions is that the force to which a bond is exposed can be significantly underestimated; in general by similar to 32-46%, where the influence of the surface corrections dominate ( the parallel and normal correction coefficients contribute similar to 5-8 or similar to 23-26%, respectively). The Basset force is a major contributor, up to 20%, for larger cells and shear rates. The lift force and inertia contribute when cells with radii >3 mu m have shear rates>2000 s(-1). Buoyancy contributes significantly for cells with radii > 3 mu m for shear rates<10 s(-1). Since the lifetime of a bond depends strongly on the force, both the level of approximation and the biomechanical model of the tether significantly affect the survival probability of tethered bacteria. For a cell attached by a FimH-mannose bond and an extendable tether with a shear rate of 3000 s(-1), neglecting the surface correction coefficients or the Basset force can imply that the survival probability is overestimated by more than an order of magnitude. This work thus shows that in order to quantitatively assess bacterial attachment forces and survival probabilities, both the fluid forces and the tether properties need to be modeled accurately.

  • 29.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    The shaft of the type 1 fimbriae regulates an externalforce to match the FimH catch bond2013In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 104, no 10, p. 2137-2148Article in journal (Refereed)
    Abstract [en]

    Type 1 fimbriae mediate adhesion of uropathogenic Escherichia coli to host cells. It has been hypothesized that due to their ability to uncoil under exposure to force, fimbriae can reduce fluid shear stress on the adhesin-receptor interaction by which the bacterium adheres to the surface. In this work, we develop a model that describes how the force on the adhesin-receptor interaction of a type 1 fimbria varies as a bacterium is affected by a time-dependent fluid flow mimicking in vivo conditions. The model combines in vivo hydrodynamic conditions with previously assessed biomechanical properties of the fimbriae. Numerical methods are used to solve for the motion and adhesion force under the presence of time-dependent fluid profiles. It is found that a bacterium tethered with a type 1 pilus will experience significantly reduced shear stress for moderate to high flow velocities and that the maximum stress the adhesin will experience is limited to ∼120 pN, which is sufficient to activate the conformational change of the FimH adhesin into its stronger state but also lower than the force required for breaking it under rapid loading. Our model thus supports the assumption that the type 1 fimbria shaft and the FimH adhesin-receptor interaction are optimized to each other, and that they give piliated bacteria significant advantages in rapidly changing fluidic environments.

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    The Shaft of the Type 1 Fimbriae Regulates an External Force to Match the FimH Catch Bond
  • 30.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Lacoursiere, Claude
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Rigid multibody simulation of a helix-like structure: the dynamics of bacterial adhesion pili2015In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 44, no 5, p. 291-300Article in journal (Refereed)
    Abstract [en]

    We present a coarse-grained rigid multibody model of a subunit assembled helix-like polymer, e.g., adhesion pili expressed by bacteria, that is capable of describing the polymer's force-extension response. With building blocks representing individual subunits, the model appropriately describes the complex behavior of pili expressed by the gram-negative uropathogenic Escherichia coli bacteria under the action of an external force. Numerical simulations show that the dynamics of the model, which include the effects of both unwinding and rewinding, are in good quantitative agreement with the characteristic force-extension response as observed experimentally for type 1 and P pili. By tuning the model, it is also possible to reproduce the force-extension response in the presence of anti-shaft antibodies, which dramatically changes the mechanical properties. Thus, the model and results in this work give enhanced understanding of how a pilus unwinds under the action of external forces and provide a new perspective of the complex bacterial adhesion processes.

  • 31.
    Zelan, Martin
    et al.
    Measurement Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Technology, RISE Research Institutes of Sweden, SE-501 15 Borås, Sweden.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Recent advances in Fabry-Péro-based refractometry utilizing gas modulation for assessment of pressure2020In: Acta IMEKO, ISSN 0237-028X, Vol. 9, no 5, p. 299-304Article in journal (Refereed)
    Abstract [en]

    Gas modulation refractometry (GAMOR) is a methodology that can mitigate the influence of fluctuations and drifts in Fabry-Pérot cavity–based refractometry. This paper presents a thorough description of its principles, what it enables, and its applicability. An overview of the latest results is presented, including the realization of a system based upon a cavity spacer made of Invar that allows for detection of N2 with sub-ppm precision, and a characterization procedure that allows for assessment of N2 with an accuracy at low-ppm levels.

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