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Reyes Garza R, Kyriakopoulos N, Cenev ZM, Rigoni C, Timonen JVI. Magnetic Quincke rollers with tunable single-particle dynamics and collective states. SCIENCE ADVANCES 2023; 9:eadh2522. [PMID: 37390203 DOI: 10.1126/sciadv.adh2522] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Accepted: 05/25/2023] [Indexed: 07/02/2023]
Abstract
Electrohydrodynamically driven active particles based on Quincke rotation have quickly become an important model system for emergent collective behavior in nonequilibrium colloidal systems. Like most active particles, Quincke rollers are intrinsically nonmagnetic, preventing the use of magnetic fields to control their complex dynamics on the fly. Here, we report on magnetic Quincke rollers based on silica particles doped with superparamagnetic iron oxide nanoparticles. We show that their magnetic nature enables the application of both externally controllable forces and torques at high spatial and temporal precision, leading to several versatile control mechanisms for their single-particle dynamics and collective states. These include tunable interparticle interactions, potential energy landscapes, and advanced programmable and teleoperated behaviors, allowing us to discover and probe active chaining, anisotropic active sedimentation-diffusion equilibria, and collective states in various geometries and dimensionalities.
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Affiliation(s)
- Ricardo Reyes Garza
- Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, Espoo FI-02150, Finland
| | - Nikos Kyriakopoulos
- Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, Espoo FI-02150, Finland
| | - Zoran M Cenev
- Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, Espoo FI-02150, Finland
| | - Carlo Rigoni
- Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, Espoo FI-02150, Finland
| | - Jaakko V I Timonen
- Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, Espoo FI-02150, Finland
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2
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Direct Measurement of the Stall Torque of the Flagellar Motor in Escherichia coli with Magnetic Tweezers. mBio 2022; 13:e0078222. [PMID: 35699374 PMCID: PMC9426426 DOI: 10.1128/mbio.00782-22] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The flagellar motor drives the rotation of flagellar filaments, propelling the swimming of flagellated bacteria. The maximum torque the motor generates, the stall torque, is a key characteristic of the motor function. Direct measurements of the stall torque carried out 3 decades ago suffered from large experimental uncertainties, and subsequently there were only indirect measurements. Here, we applied magnetic tweezers to directly measure the stall torque in E. coli. We precisely calibrated the torsional stiffness of the magnetic tweezers and performed motor resurrection experiments at stall, accomplishing a precise determination of the stall torque per torque-generating unit (stator unit). From our measurements, each stator passes 2 protons per step, indicating a tight coupling between motor rotation and proton flux. IMPORTANCE The maximum torque the bacterial flagellar motor generates, the stall torque, is a critical parameter that describes the motor energetics. As the motor operates in equilibrium near stall, from the stall torque one can determine how many protons each torque-generating unit (stator) of the motor passes per revolution and then test whether motor rotation and proton flux are tightly or loosely coupled, which has been controversial in recent years. Direct measurements performed 3 decades ago suffered from large uncertainties, and subsequently, only indirect measurements were attempted, obtaining a range of values inconsistent with the previous direct measurements. Here, we developed a method that used magnetic tweezers to perform motor resurrection experiments at stall, resulting in a direct precise measurement of the stall torque per stator. Our study resolved the previous inconsistencies and provided direct experimental support for the tight coupling mechanism between motor rotation and proton flux.
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3
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Abstract
Bacteria thrive both in liquids and attached to surfaces. The concentration of bacteria on surfaces is generally much higher than in the surrounding environment, offering bacteria ample opportunity for mutualistic, symbiotic, and pathogenic interactions. To efficiently populate surfaces, they have evolved mechanisms to sense mechanical or chemical cues upon contact with solid substrata. This is of particular importance for pathogens that interact with host tissue surfaces. In this review we discuss how bacteria are able to sense surfaces and how they use this information to adapt their physiology and behavior to this new environment. We first survey mechanosensing and chemosensing mechanisms and outline how specific macromolecular structures can inform bacteria about surfaces. We then discuss how mechanical cues are converted to biochemical signals to activate specific cellular processes in a defined chronological order and describe the role of two key second messengers, c-di-GMP and cAMP, in this process.
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Affiliation(s)
| | - Urs Jenal
- Biozentrum, University of Basel, CH-4056 Basel, Switzerland; ,
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4
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Velho Rodrigues MF, Lisicki M, Lauga E. The bank of swimming organisms at the micron scale (BOSO-Micro). PLoS One 2021; 16:e0252291. [PMID: 34111118 PMCID: PMC8191957 DOI: 10.1371/journal.pone.0252291] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Accepted: 05/13/2021] [Indexed: 12/24/2022] Open
Abstract
Unicellular microscopic organisms living in aqueous environments outnumber all other creatures on Earth. A large proportion of them are able to self-propel in fluids with a vast diversity of swimming gaits and motility patterns. In this paper we present a biophysical survey of the available experimental data produced to date on the characteristics of motile behaviour in unicellular microswimmers. We assemble from the available literature empirical data on the motility of four broad categories of organisms: bacteria (and archaea), flagellated eukaryotes, spermatozoa and ciliates. Whenever possible, we gather the following biological, morphological, kinematic and dynamical parameters: species, geometry and size of the organisms, swimming speeds, actuation frequencies, actuation amplitudes, number of flagella and properties of the surrounding fluid. We then organise the data using the established fluid mechanics principles for propulsion at low Reynolds number. Specifically, we use theoretical biophysical models for the locomotion of cells within the same taxonomic groups of organisms as a means of rationalising the raw material we have assembled, while demonstrating the variability for organisms of different species within the same group. The material gathered in our work is an attempt to summarise the available experimental data in the field, providing a convenient and practical reference point for future studies.
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Affiliation(s)
- Marcos F. Velho Rodrigues
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom
| | - Maciej Lisicki
- Faculty of Physics, University of Warsaw, Warsaw, Poland
| | - Eric Lauga
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom
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5
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Wang X, Law J, Luo M, Gong Z, Yu J, Tang W, Zhang Z, Mei X, Huang Z, You L, Sun Y. Magnetic Measurement and Stimulation of Cellular and Intracellular Structures. ACS NANO 2020; 14:3805-3821. [PMID: 32223274 DOI: 10.1021/acsnano.0c00959] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
From single-pole magnetic tweezers to robotic magnetic-field generation systems, the development of magnetic micromanipulation systems, using electromagnets or permanent magnets, has enabled a multitude of applications for cellular and intracellular measurement and stimulation. Controlled by different configurations of magnetic-field generation systems, magnetic particles have been actuated by an external magnetic field to exert forces/torques and perform mechanical measurements on the cell membrane, cytoplasm, cytoskeleton, nucleus, intracellular motors, etc. The particles have also been controlled to generate aggregations to trigger cell signaling pathways and produce heat to cause cancer cell apoptosis for hyperthermia treatment. Magnetic micromanipulation has become an important tool in the repertoire of toolsets for cell measurement and stimulation and will continue to be used widely for further explorations of cellular/intracellular structures and their functions. Existing review papers in the literature focus on fabrication and position control of magnetic particles/structures (often termed micronanorobots) and the synthesis and functionalization of magnetic particles. Differently, this paper reviews the principles and systems of magnetic micromanipulation specifically for cellular and intracellular measurement and stimulation. Discoveries enabled by magnetic measurement and stimulation of cellular and intracellular structures are also summarized. This paper ends with discussions on future opportunities and challenges of magnetic micromanipulation in the exploration of cellular biophysics, mechanotransduction, and disease therapeutics.
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Affiliation(s)
- Xian Wang
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario M5S 3G9, Canada
| | - Junhui Law
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
| | - Mengxi Luo
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
| | - Zheyuan Gong
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
| | - Jiangfan Yu
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
| | - Wentian Tang
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
| | - Zhuoran Zhang
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
| | - Xueting Mei
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario M5S 3G9, Canada
| | - Zongjie Huang
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
| | - Lidan You
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario M5S 3G9, Canada
| | - Yu Sun
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario M5S 3G9, Canada
- Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario M5S 3G4, Canada
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6
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Lak A, Kahmann T, Schaper SJ, Obel J, Ludwig F, Müller-Buschbaum P, Lipfert J. The Dissociation Rate of Acetylacetonate Ligands Governs the Size of Ferrimagnetic Zinc Ferrite Nanocubes. ACS APPLIED MATERIALS & INTERFACES 2020; 12:217-226. [PMID: 31804796 DOI: 10.1021/acsami.9b17714] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Magnetic nanoparticles are critical to a broad range of applications from medical diagnostics and therapeutics to biotechnological processes and single-molecule manipulation. To advance these applications, facile and robust routes to synthesize highly magnetic nanoparticles over a wide size range are needed. Here, we demonstrate that changing the degassing temperature of thermal decomposition of metal acetylacetonate precursors from 90 to 25 °C tunes the size of ferrimagnetic ZnxFe3-xO4 nanocubes from 25 to 100 nm, respectively. We show that degassing at 90 °C nearly entirely removes acetylacetone ligands from the reaction, which results in an early formation of monomers and a reaction-controlled growth following LaMer's model toward small nanocubes. In contrast, degassing at 25 °C only partially dissociates acetylacetone ligands from the metal center and triggers a delayed formation of monomers, which leads to intermediate assembled structures made of tiny irregular crystallites and an eventual formation of large nanocubes via a diffusion-controlled growth mechanism. Using complementary techniques, we determine the substitution fraction x of Zn2+ to be in the range of 0.35-0.37. Our method reduces the complexity of the thermal decomposition method by narrowing the synthesis parameter space to a single physical parameter and enables fabrication of highly magnetic and uniform zinc ferrite nanocubes over a broad size range. The resulting particles are promising for a range of applications from magnetic fluid hyperthermia to actuation of macromolecules.
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Affiliation(s)
- Aidin Lak
- Department of Physics and Center for NanoScience , LMU Munich , Amalienstr. 54 , 80799 Munich , Germany
| | - Tamara Kahmann
- Institute for Electrical Measurement Science and Fundamental Electrical Engineering , Technische Universität Braunschweig , Hans-Sommer-Str. 66 , 38106 Braunschweig , Germany
| | - Simon Jakob Schaper
- Lehrstuhl für Funktionelle Materialien, Physik-Department , Technische Universität München , James-Franck-Str. 1 , 85748 Garching , Germany
| | - Jaroslava Obel
- Department of Chemistry and Pharmacy, Analytical Division , LMU Munich , Butenandtstr. 5-13 , 81377 Munich , Germany
| | - Frank Ludwig
- Institute for Electrical Measurement Science and Fundamental Electrical Engineering , Technische Universität Braunschweig , Hans-Sommer-Str. 66 , 38106 Braunschweig , Germany
| | - Peter Müller-Buschbaum
- Lehrstuhl für Funktionelle Materialien, Physik-Department , Technische Universität München , James-Franck-Str. 1 , 85748 Garching , Germany
| | - Jan Lipfert
- Department of Physics and Center for NanoScience , LMU Munich , Amalienstr. 54 , 80799 Munich , Germany
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7
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Nord AL, Pedaci F. Mechanisms and Dynamics of the Bacterial Flagellar Motor. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1267:81-100. [PMID: 32894478 DOI: 10.1007/978-3-030-46886-6_5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Many bacteria are able to actively propel themselves through their complex environment, in search of resources and suitable niches. The source of this propulsion is the Bacterial Flagellar Motor (BFM), a molecular complex embedded in the bacterial membrane which rotates a flagellum. In this chapter we review the known physical mechanisms at work in the motor. The BFM shows a highly dynamic behavior in its power output, its structure, and in the stoichiometry of its components. Changes in speed, rotation direction, constituent protein conformations, and the number of constituent subunits are dynamically controlled in accordance to external chemical and mechanical cues. The mechano-sensitivity of the motor is likely related to the surface-sensing ability of bacteria, relevant in the initial stage of biofilm formation.
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Affiliation(s)
- A L Nord
- Centre de Biochimie Structurale (CBS), INSERM, CNRS, University of Montpellier, Montpellier, France
| | - F Pedaci
- Centre de Biochimie Structurale (CBS), INSERM, CNRS, University of Montpellier, Montpellier, France.
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8
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Martínez-Santiago CJ, Quiñones E. On matching the magnetic torque exerted by a rotating magnetic field to the torsional stiffness of braided DNA molecules for torque estimations. Chem Phys 2019. [DOI: 10.1016/j.chemphys.2018.12.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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9
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Zhang S, Shakiba N, Chen Y, Zhang Y, Tian P, Singh J, Chamberlain MD, Satkauskas M, Flood AG, Kherani NP, Yu S, Zandstra PW, Wheeler AR. Patterned Optoelectronic Tweezers: A New Scheme for Selecting, Moving, and Storing Dielectric Particles and Cells. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2018; 14:e1803342. [PMID: 30307718 DOI: 10.1002/smll.201803342] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Indexed: 06/08/2023]
Abstract
Optical micromanipulation has become popular for a wide range of applications. In this work, a new type of optical micromanipulation platform, patterned optoelectronic tweezers (p-OET), is introduced. In p-OET devices, the photoconductive layer (that is continuous in a conventional OET device) is patterned, forming regions in which the electrode layer is locally exposed. It is demonstrated that micropatterns in the photoconductive layer are useful for repelling unwanted particles/cells, and also for keeping selected particles/cells in place after turning off the light source, minimizing light-induced heating. To clarify the physical mechanism behind these effects, systematic simulations are carried out, which indicate the existence of strong nonuniform electric fields at the boundary of micropatterns. The simulations are consistent with experimental observations, which are explored for a wide variety of geometries and conditions. It is proposed that the new technique may be useful for myriad applications in the rapidly growing area of optical micromanipulation.
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Affiliation(s)
- Shuailong Zhang
- Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON, M5S 3E1, Canada
- Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada
- Institute for Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, M5S 3G9, Canada
| | - Nika Shakiba
- Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON, M5S 3E1, Canada
- Institute for Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, M5S 3G9, Canada
| | - Yujie Chen
- State Key Laboratory of Optoelectronic Materials and Technologies, School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou, 510275, China
| | - Yanfeng Zhang
- State Key Laboratory of Optoelectronic Materials and Technologies, School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou, 510275, China
| | - Pengfei Tian
- Institute for Electric Light Sources, Fudan University, Shanghai, 200433, China
| | - Jastaranpreet Singh
- Institute for Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, M5S 3G9, Canada
| | - M Dean Chamberlain
- Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON, M5S 3E1, Canada
- Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada
- Institute for Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, M5S 3G9, Canada
| | - Monika Satkauskas
- Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON, M5S 3E1, Canada
- Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada
| | - Andrew G Flood
- Department of Electrical and Computer Engineering, University of Toronto, Toronto, ON, M5S 3G4, Canada
| | - Nazir P Kherani
- Department of Electrical and Computer Engineering, University of Toronto, Toronto, ON, M5S 3G4, Canada
- Department of Materials Science and Engineering, University of Toronto, Toronto, ON, M5S 3E4, Canada
| | - Siyuan Yu
- State Key Laboratory of Optoelectronic Materials and Technologies, School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou, 510275, China
- Photonics Group, Merchant Venturers School of Engineering, University of Bristol, Bristol, BS81UB, UK
| | - Peter W Zandstra
- Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON, M5S 3E1, Canada
- Institute for Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, M5S 3G9, Canada
- Medicine by Design, University of Toronto, Toronto, ON, M5S 3G9, Canada
- School of Biomedical Engineering, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada
- Michael Smith Laboratories, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada
| | - Aaron R Wheeler
- Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON, M5S 3E1, Canada
- Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada
- Institute for Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, M5S 3G9, Canada
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10
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Abstract
The rotary motor of bacteria is a natural nano-technological marvel that enables cell locomotion by powering the rotation of semi-rigid helical flagellar filaments in fluid environments. It is well known that the motor operates essentially at constant torque in counter-clockwise direction but past work have reported a large range of values of this torque. Focusing on Escherichia coli cells that are swimming and cells that are stuck on a glass surface for which all geometrical and environmental parameters are known (N. C. Darnton et al., J. Bacteriol., 2007, 189, 1756-1764), we use two validated numerical methods to compute the value of the motor torque consistent with experiments. Specifically, we use (and compare) a numerical method based on the boundary integral representation of Stokes flow and also develop a hybrid method combining boundary element and slender body theory to model the cell body and flagellar filament, respectively. Using measured rotation speed of the motor, our computations predict a value of the motor torque in the range 440 pN nm to 829 pN nm, depending critically on the distance between the flagellar filaments and the nearby surface.
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Affiliation(s)
- Debasish Das
- Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK.
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11
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Martínez-Santiago CJ, Quiñones E. Magnetic modulation of the unbraiding dynamics of pairs of DNA molecules to model the system as an intermittent oscillator. Chem Phys 2018. [DOI: 10.1016/j.chemphys.2017.12.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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12
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Kriegel F, Vanderlinden W, Nicolaus T, Kardinal A, Lipfert J. Measuring Single-Molecule Twist and Torque in Multiplexed Magnetic Tweezers. Methods Mol Biol 2018; 1814:75-98. [PMID: 29956228 DOI: 10.1007/978-1-4939-8591-3_6] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Magnetic tweezers permit application of precisely calibrated stretching forces to nucleic acid molecules tethered between a surface and superparamagnetic beads. In addition, magnetic tweezers can control the tethers' twist. Here, we focus on recent extensions of the technique that expand the capabilities of conventional magnetic tweezers by enabling direct measurements of single-molecule torque and twist. Magnetic torque tweezers (MTT) still control the DNA or RNA tether's twist, but directly measure molecular torque by monitoring changes in the equilibrium rotation angle upon overwinding and underwinding of the tether. In freely orbiting magnetic tweezers (FOMT), one end of the tether is allowed to rotate freely, while still applying stretching forces and monitoring rotation angle. Both MTT and FOMT have provided unique insights into the mechanical properties, structural transitions, and interactions of DNA and RNA. Here, we provide step-by-step protocols to carry out FOMT and MTT measurements. In particular, we focus on multiplexed measurements, i.e., measurements that record data for multiple nucleic acid tethers at the same time, to improve statistics and to facilitate the observation of rare events.
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Affiliation(s)
- Franziska Kriegel
- Department of Physics, Nanosystems Initiative Munich, and Center for Nanoscience, LMU Munich, Munich, Germany
| | - Willem Vanderlinden
- Department of Physics, Nanosystems Initiative Munich, and Center for Nanoscience, LMU Munich, Munich, Germany.,Division of Molecular Imaging and Photonics, Department of Chemistry, KU Leuven-University of Leuven, Leuven, Belgium
| | - Thomas Nicolaus
- Department of Physics, Nanosystems Initiative Munich, and Center for Nanoscience, LMU Munich, Munich, Germany
| | - Angelika Kardinal
- Department of Physics, Nanosystems Initiative Munich, and Center for Nanoscience, LMU Munich, Munich, Germany
| | - Jan Lipfert
- Department of Physics, Nanosystems Initiative Munich, and Center for Nanoscience, LMU Munich, Munich, Germany.
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