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Eremchev M, Roesel D, Dansette PM, Michailovas A, Roke S. High throughput wide field second harmonic imaging of giant unilamellar vesicles. Biointerphases 2023; 18:031202. [PMID: 37289033 DOI: 10.1116/6.0002640] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2023] [Accepted: 05/16/2023] [Indexed: 06/09/2023] Open
Abstract
Cell-sized giant unilamellar vesicles (GUVs) are an ideal tool for understanding lipid membrane structure and properties. Label-free spatiotemporal images of their membrane potential and structure would greatly aid the quantitative understanding of membrane properties. In principle, second harmonic imaging is a great tool to do so, but the low degree of spatial anisotropy that arises from a single membrane limits its application. Here, we advance the use of wide-field high throughput SH imaging by SH imaging with the use of ultrashort laser pulses. We achieve a throughput improvement of 78% of the maximum theoretical value and demonstrate subsecond image acquisition times. We show how the interfacial water intensity can be converted into a quantitative membrane potential map. Finally, for GUV imaging, we compare this type of nonresonant SH imaging to resonant SH imaging and two photon imaging using fluorophores.
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Affiliation(s)
- M Eremchev
- Laboratory for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), School of Engineerinsg (STI), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - D Roesel
- Laboratory for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), School of Engineerinsg (STI), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - P-M Dansette
- Ekspla Ltd., Savanoriu Ave. 237, LT-02300 Vilnius, Lithuania
| | - A Michailovas
- Ekspla Ltd., Savanoriu Ave. 237, LT-02300 Vilnius, Lithuania
- Center for Physical Sciences and Technology, Savanoriu Ave. 231, LT-02300 Vilnius, Lithuania
| | - S Roke
- Laboratory for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), School of Engineerinsg (STI), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Institute of Materials Science and Engineering (IMX), School of Engineering (STI), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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2
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Eremchev M, Roesel D, Poojari CS, Roux A, Hub JS, Roke S. Passive transport of Ca 2+ ions through lipid bilayers imaged by widefield second harmonic microscopy. Biophys J 2023; 122:624-631. [PMID: 36659849 PMCID: PMC9989880 DOI: 10.1016/j.bpj.2023.01.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 01/04/2023] [Accepted: 01/17/2023] [Indexed: 01/21/2023] Open
Abstract
In biology, release of Ca2+ ions in the cytosol is essential to trigger or control many cell functions. Calcium signaling acutely depends on lipid membrane permeability to Ca2+. For proper understanding of membrane permeability to Ca2+, both membrane hydration and the structure of the hydrophobic core must be taken into account. Here, we vary the hydrophobic core of bilayer membranes and observe different types of behavior in high-throughput wide-field second harmonic imaging. Ca2+ translocation is observed through mono-unsaturated (DOPC:DOPA) membranes, reduced upon the addition of cholesterol, and completely inhibited for branched (DPhPC:DPhPA) and poly-unsaturated (SLPC:SLPA) lipid membranes. We propose, using molecular dynamics simulations, that ion transport occurs through ion-induced transient pores, which requires nonequilibrium membrane restructuring. This results in different rates at different locations and suggests that the hydrophobic structure of lipids plays a much more sophisticated regulating role than previously thought.
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Affiliation(s)
- Maksim Eremchev
- Laboratory for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), School of Engineering (STI), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - David Roesel
- Laboratory for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), School of Engineering (STI), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Chetan S Poojari
- Theoretical Physics and Center for Biophysics, Saarland University, Saarbrücken, Germany
| | - Aurélien Roux
- Biochemistry Department, University of Geneva, Geneva, Switzerland; Swiss National Centre for Competence in Research Programme Chemical Biology, Geneva, Switzerland; School of Chemistry and Biochemistry, University of Geneva, Geneva, Switzerland
| | - Jochen S Hub
- Theoretical Physics and Center for Biophysics, Saarland University, Saarbrücken, Germany
| | - Sylvie Roke
- Laboratory for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), School of Engineering (STI), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; Institute of Materials Science and Engineering (IMX), School of Engineering (STI), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
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3
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Roesel D, Eremchev M, Poojari CS, Hub JS, Roke S. Ion-Induced Transient Potential Fluctuations Facilitate Pore Formation and Cation Transport through Lipid Membranes. J Am Chem Soc 2022; 144:23352-23357. [PMID: 36521841 PMCID: PMC9801421 DOI: 10.1021/jacs.2c08543] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Indexed: 12/23/2022]
Abstract
Unassisted ion transport through lipid membranes plays a crucial role in many cell functions without which life would not be possible, yet the precise mechanism behind the process remains unknown due to its molecular complexity. Here, we demonstrate a direct link between membrane potential fluctuations and divalent ion transport. High-throughput wide-field non-resonant second harmonic (SH) microscopy of membrane water shows that membrane potential fluctuations are universally found in lipid bilayer systems. Molecular dynamics simulations reveal that such variations in membrane potential reduce the free energy cost of transient pore formation and increase the ion flux across an open pore. These transient pores can act as conduits for ion transport, which we SH image for a series of divalent cations (Cu2+, Ca2+, Ba2+, Mg2+) passing through giant unilamellar vesicle (GUV) membranes. Combining the experimental and computational results, we show that permeation through pores formed via an ion-induced electrostatic field is a viable mechanism for unassisted ion transport.
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Affiliation(s)
- David Roesel
- Laboratory
for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI),
School of Engineering (STI), École
Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Maksim Eremchev
- Laboratory
for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI),
School of Engineering (STI), École
Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Chetan S. Poojari
- Theoretical
Physics and Center for Biophysics, Saarland
University, 66123 Saarbrücken, Germany
| | - Jochen S. Hub
- Theoretical
Physics and Center for Biophysics, Saarland
University, 66123 Saarbrücken, Germany
| | - Sylvie Roke
- Laboratory
for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI),
School of Engineering (STI), École
Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Institute
of Materials Science and Engineering (IMX), School of Engineering
(STI), École Polytechnique Fédérale
de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Lausanne
Centre for Ultrafast Science, École
Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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4
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de Coene Y, Jooken S, Deschaume O, Van Steenbergen V, Vanden Berghe P, Van den Haute C, Baekelandt V, Callewaert G, Van Cleuvenbergen S, Verbiest T, Bartic C, Clays K. Label-Free Imaging of Membrane Potentials by Intramembrane Field Modulation, Assessed by Second Harmonic Generation Microscopy. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2200205. [PMID: 35355419 DOI: 10.1002/smll.202200205] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Revised: 03/03/2022] [Indexed: 06/14/2023]
Abstract
Optical interrogation of cellular electrical activity has proven itself essential for understanding cellular function and communication in complex networks. Voltage-sensitive dyes are important tools for assessing excitability but these highly lipophilic sensors may affect cellular function. Label-free techniques offer a major advantage as they eliminate the need for these external probes. In this work, it is shown that endogenous second-harmonic generation (SHG) from live cells is highly sensitive to changes in transmembrane potential (TMP). Simultaneous electrophysiological control of a living human embryonic kidney (HEK293T) cell, through a whole-cell voltage-clamp reveals a linear relation between the SHG intensity and membrane voltage. The results suggest that due to the high ionic strengths and fast optical response of biofluids, membrane hydration is not the main contributor to the observed field sensitivity. A conceptual framework is further provided that indicates that the SHG voltage sensitivity reflects the electric field within the biological asymmetric lipid bilayer owing to a nonzero χeff(2) tensor. Changing the TMP without surface modifications such as electrolyte screening offers high optical sensitivity to membrane voltage (≈40% per 100 mV), indicating the power of SHG for label-free read-out. These results hold promise for the design of a non-invasive label-free read-out tool for electrogenic cells.
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Affiliation(s)
- Yovan de Coene
- Laboratory of Molecular Imaging and Photonics, Department of Chemistry, KU Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium
| | - Stijn Jooken
- Laboratory of Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium
| | - Olivier Deschaume
- Laboratory of Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium
| | - Valérie Van Steenbergen
- Laboratory for Enteric NeuroScience (LENS), TAGRID, Department of Chronic Diseases Metabolism and Ageing, Ku Leuven, ON I Herestraat 49, Leuven, 3000, Belgium
| | - Pieter Vanden Berghe
- Laboratory for Enteric NeuroScience (LENS), TAGRID, Department of Chronic Diseases Metabolism and Ageing, Ku Leuven, ON I Herestraat 49, Leuven, 3000, Belgium
| | - Chris Van den Haute
- Laboratory for Neurobiology and Gene Therapy, Department of Neurosciences, Ku Leuven, RK-Herestraat 49, Leuven, 3000, Belgium
| | - Veerle Baekelandt
- Laboratory for Neurobiology and Gene Therapy, Department of Neurosciences, Ku Leuven, RK-Herestraat 49, Leuven, 3000, Belgium
| | - Geert Callewaert
- Department of Cellular and Molecular Medicine, Ku Leuven, KULAK Kortrijk Campus, Etienne Sabbelaan 53, Kortrijk, 8500, Belgium
| | - Stijn Van Cleuvenbergen
- Laboratory of Molecular Imaging and Photonics, Department of Chemistry, KU Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium
| | - Thierry Verbiest
- Laboratory of Molecular Imaging and Photonics, Department of Chemistry, KU Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium
| | - Carmen Bartic
- Laboratory of Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium
| | - Koen Clays
- Laboratory of Molecular Imaging and Photonics, Department of Chemistry, KU Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium
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Sly KL, Conboy JC. Second Harmonic Correlation Spectroscopy: Theory and Principles for Determining Surface Binding Kinetics. APPLIED SPECTROSCOPY 2017; 71:1368-1379. [PMID: 28534678 DOI: 10.1177/0003702816681797] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A novel application of second harmonic correlation spectroscopy (SHCS) for the direct determination of molecular adsorption and desorption kinetics to a surface is discussed in detail. The surface-specific nature of second harmonic generation (SHG) provides an efficient means to determine the kinetic rates of adsorption and desorption of molecular species to an interface without interference from bulk diffusion, which is a significant limitation of fluorescence correlation spectroscopy (FCS). The underlying principles of SHCS for the determination of surface binding kinetics are presented, including the role of optical coherence and optical heterodyne mixing. These properties of SHCS are extremely advantageous and lead to an increase in the signal-to-noise (S/N) of the correlation data, increasing the sensitivity of the technique. The influence of experimental parameters, including the uniformity of the TEM00 laser beam, the overall photon flux, and collection time are also discussed, and are shown to significantly affect the S/N of the correlation data. Second harmonic correlation spectroscopy is a powerful, surface-specific, and label-free alternative to other correlation spectroscopic methods for examining surface binding kinetics.
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Affiliation(s)
- Krystal L Sly
- Department of Chemistry, University of Utah, Utah, USA
| | - John C Conboy
- Department of Chemistry, University of Utah, Utah, USA
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Macias-Romero C, Didier MEP, Jourdain P, Marquet P, Magistretti P, Tarun OB, Zubkovs V, Radenovic A, Roke S. High throughput second harmonic imaging for label-free biological applications. OPTICS EXPRESS 2014; 22:31102-31112. [PMID: 25607059 DOI: 10.1364/oe.22.031102] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Second harmonic generation (SHG) is inherently sensitive to the absence of spatial centrosymmetry, which can render it intrinsically sensitive to interfacial processes, chemical changes and electrochemical responses. Here, we seek to improve the imaging throughput of SHG microscopy by using a wide-field imaging scheme in combination with a medium-range repetition rate amplified near infrared femtosecond laser source and gated detection. The imaging throughput of this configuration is tested by measuring the optical image contrast for different image acquisition times of BaTiO₃ nanoparticles in two different wide-field setups and one commercial point-scanning configuration. We find that the second harmonic imaging throughput is improved by 2-3 orders of magnitude compared to point-scan imaging. Capitalizing on this result, we perform low fluence imaging of (parts of) living mammalian neurons in culture.
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