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Kumar A, Bharadwaj A, Choudhury P, Mathew SP, Jaganathan BG, Boruah BR. Tuning the excitation laser power in a stochastic optical reconstruction microscope for Alexa Fluor 647 dye in Vectashield mounting media. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2024; 95:083701. [PMID: 39087814 DOI: 10.1063/5.0217409] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2024] [Accepted: 07/14/2024] [Indexed: 08/02/2024]
Abstract
Super-resolution imaging techniques have fundamentally changed our understanding of cellular architecture and dynamics by surpassing the diffraction limit and enabling the visualization of subcellular details. The popular super-resolution method known as stochastic optical reconstruction microscopy (STORM) relies on the exact localization of single fluorescent molecules. The significance of employing Vectashield as a mounting medium for the super-resolution imaging scheme called direct STORM has recently been explored. Alexa Fluor 647 (AF647), one of the most popular dyes, shows significant blinking in Vectashield. However, to observe prominent blinking of the fluorophore for the reconstruction of super-resolved images, the power of the excitation laser needs to be tuned. This work demonstrates the tuning of excitation power density in the sample plane for superior imaging performance using AF647 in Vectashield. Samples comprising MDA-MB-231 breast cancer cell line are used for the experiments. The actin filaments of the cell are stained with phalloidin-conjugated AF647 dye. For the experiment, we employ a low-cost openFrame-based STORM system equipped with a programmable Arduino-regulated laser source emitting at 638 nm. An excitation power density of 0.60 kW/cm2 at 638 nm in the sample plane is observed to maximize the signal-to-noise ratio, the number of switching events, and the number of photons detected per event during image acquisition, thereby leading to the best imaging performance in terms of resolution. The outcome of this work will promote further STORM-based super-resolved imaging applications in cell biology using Alexa Fluor 647 in Vectashield.
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Affiliation(s)
- Amalesh Kumar
- Department of Physics, IIT Guwahati, Guwahati 781039, Assam, India
| | - Anupam Bharadwaj
- Department of Physics, IIT Guwahati, Guwahati 781039, Assam, India
| | | | - Sam P Mathew
- Department of Bioscience and Bioengineering, IIT Guwahati, Guwahati 781039, Assam, India
| | - Bithiah Grace Jaganathan
- Department of Bioscience and Bioengineering, IIT Guwahati, Guwahati 781039, Assam, India
- Jyoti and Bhupat Mehta School of Health Sciences and Technology, IIT Guwahati, Guwahati 781039, Assam, India
| | - Bosanta R Boruah
- Department of Physics, IIT Guwahati, Guwahati 781039, Assam, India
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2
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Saladin L, Breton V, Le Berruyer V, Nazac P, Lequeu T, Didier P, Danglot L, Collot M. Targeted Photoconvertible BODIPYs Based on Directed Photooxidation-Induced Conversion for Applications in Photoconversion and Live Super-Resolution Imaging. J Am Chem Soc 2024; 146:17456-17473. [PMID: 38861358 DOI: 10.1021/jacs.4c05231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2024]
Abstract
Photomodulable fluorescent probes are drawing increasing attention due to their applications in advanced bioimaging. Whereas photoconvertible probes can be advantageously used in tracking, photoswitchable probes constitute key tools for single-molecule localization microscopy to perform super-resolution imaging. Herein, we shed light on a red and far-red BODIPY, namely, BDP-576 and BDP-650, which possess both properties of conversion and switching. Our study demonstrates that these pyrrolyl-BODIPYs convert into typical green- and red-emitting BODIPYs that are perfectly adapted to microscopy. We also showed that this pyrrolyl-BODIPYs undergo Directed Photooxidation Induced Conversion, a photoconversion mechanism that we recently introduced, where the pyrrole moiety plays a central role. These unique features were used to develop targeted photoconvertible probes toward different organelles or subcellular units (plasma membrane, mitochondria, nucleus, actin, Golgi apparatus, etc.) using chemical targeting moieties and a Halo tag. We notably showed that BDP-650 could be used to track intracellular vesicles over more than 20 min in two-color imagings with laser scanning confocal microscopy, demonstrating its robustness. The switching properties of these photoconverters were studied at the single-molecule level and were then successfully used in live single-molecule localization microscopy in epithelial cells and neurons. Both membrane- and mitochondria- targeted probes could be used to decipher membrane 3D architecture and mitochondrial dynamics at the nanoscale. This study builds a bridge between the photoconversion and photoswitching properties of probes undergoing directed photooxidation and shows the versatility and efficacy of this mechanism in advanced live imaging.
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Affiliation(s)
- Lazare Saladin
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, CNRS/Université de Strasbourg, 74 route du Rhin, 67401 Illkirch-Graffenstaden, France
| | - Victor Breton
- Université Paris Cité, Institute of Psychiatry and Neuroscience of Paris (IPNP), INSERM U1266, Membrane Traffic in Healthy and Diseased Brain team; NeurImag core facility scientific director, 75014 Paris, France
| | - Valentine Le Berruyer
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, CNRS/Université de Strasbourg, 74 route du Rhin, 67401 Illkirch-Graffenstaden, France
- Chemistry of Photoresponsive Systems, Laboratoire de Chémo-Biologie Synthétique et Thérapeutique (CBST) UMR 7199, CNRS, Université de Strasbourg, F-67400 Illkirch, France
| | - Paul Nazac
- Université Paris Cité, Institute of Psychiatry and Neuroscience of Paris (IPNP), INSERM U1266, Membrane Traffic in Healthy and Diseased Brain team; NeurImag core facility scientific director, 75014 Paris, France
| | - Thiebault Lequeu
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, CNRS/Université de Strasbourg, 74 route du Rhin, 67401 Illkirch-Graffenstaden, France
| | - Pascal Didier
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, CNRS/Université de Strasbourg, 74 route du Rhin, 67401 Illkirch-Graffenstaden, France
| | - Lydia Danglot
- Université Paris Cité, Institute of Psychiatry and Neuroscience of Paris (IPNP), INSERM U1266, Membrane Traffic in healthy and Diseased brain team; NeurImag core facility scientific director, 75014 Paris, France
| | - Mayeul Collot
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, CNRS/Université de Strasbourg, 74 route du Rhin, 67401 Illkirch-Graffenstaden, France
- Chemistry of Photoresponsive Systems, Laboratoire de Chémo-Biologie Synthétique et Thérapeutique (CBST) UMR 7199, CNRS, Université de Strasbourg, F-67400 Illkirch, France
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3
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Seabury AG, Khodabocus AJ, Kogan IM, Hoy GR, DeSalvo GA, Wustholz KL. Blinking characteristics of organic fluorophores for blink-based multiplexing. Commun Chem 2024; 7:18. [PMID: 38280979 PMCID: PMC10821931 DOI: 10.1038/s42004-024-01106-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Accepted: 01/12/2024] [Indexed: 01/29/2024] Open
Abstract
Single-molecule fluorescence experiments have transformed our understanding of complex materials and biological systems. Whether single molecules are used to report on their nano-environment or provide for localization, understanding their blinking dynamics (i.e., stochastic fluctuations in emission intensity under continuous illumination) is paramount. We recently demonstrated another use for blinking dynamics called blink-based multiplexing (BBM), where individual emitters are classified using a single excitation laser based on blinking dynamics, rather than color. This study elucidates the structure-activity relationships governing BBM performance in a series of model rhodamine, BODIPY, and anthraquinone fluorophores that undergo different photo-physical and-chemical processes during blinking. Change point detection and multinomial logistic regression analyses show that BBM can leverage spectral fluctuations, electron and proton transfer kinetics, as well as photostability for molecular classification-even within the context of a shared blinking mechanism. In doing so, we demonstrate two- and three-color BBM with ≥ 93% accuracy using spectrally-overlapped fluorophores.
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Affiliation(s)
| | | | | | - Grayson R Hoy
- Chemistry Department, William & Mary, Williamsburg, VA, USA
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4
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Hoy GR, DeSalvo GA, Haile SH, Smith EN, Wustholz KL. Rapid, Accurate Classification of Single Emitters in Various Conditions and Environments for Blinking-Based Multiplexing. J Phys Chem A 2023; 127:3518-3525. [PMID: 37023466 DOI: 10.1021/acs.jpca.3c00917] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/08/2023]
Abstract
Although single-molecule imaging is widely applied in biology and materials science, most studies are limited by their reliance on spectrally distinct fluorescent probes. We recently introduced blinking-based multiplexing (BBM), a simple approach to differentiate spectrally overlapped single emitters based solely on their intrinsic blinking dynamics. The original proof-of-concept study implemented two methods for emitter classification: an empirically derived metric and a deep learning algorithm, both of which have significant drawbacks. Here, a multinomial logistic regression (LR) classification is applied to rhodamine 6G (R6G) and CdSe/ZnS quantum dots (QDs) in various experimental conditions (i.e., excitation power and bin time) and environments (i.e., glass versus polymer). We demonstrate that LR analysis is rapid and generalizable, and classification accuracies of 95% are routinely observed, even within a complex polymer environment where multiple factors contribute to blinking heterogeneity. In doing so, this study (1) reveals the experimental conditions (i.e., Pexc = 1.2 μW and tbin = 10 ms) that optimize BBM for QD and R6G and (2) demonstrates that BBM via multinomial LR can accurately classify both emitter and environment, opening the door to new opportunities in single-molecule imaging.
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Affiliation(s)
- Grayson R Hoy
- Department of Chemistry, William & Mary, P.O. Box 8795, Williamsburg, Virginia 23187, United States
| | - Grace A DeSalvo
- Department of Chemistry, William & Mary, P.O. Box 8795, Williamsburg, Virginia 23187, United States
| | - Sophia H Haile
- Department of Chemistry, William & Mary, P.O. Box 8795, Williamsburg, Virginia 23187, United States
| | - Emma N Smith
- Department of Chemistry, William & Mary, P.O. Box 8795, Williamsburg, Virginia 23187, United States
| | - Kristin L Wustholz
- Department of Chemistry, William & Mary, P.O. Box 8795, Williamsburg, Virginia 23187, United States
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5
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Choosing the Probe for Single-Molecule Fluorescence Microscopy. Int J Mol Sci 2022; 23:ijms232314949. [PMID: 36499276 PMCID: PMC9735909 DOI: 10.3390/ijms232314949] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 11/18/2022] [Accepted: 11/24/2022] [Indexed: 12/03/2022] Open
Abstract
Probe choice in single-molecule microscopy requires deeper evaluations than those adopted for less sensitive fluorescence microscopy studies. Indeed, fluorophore characteristics can alter or hide subtle phenomena observable at the single-molecule level, wasting the potential of the sophisticated instrumentation and algorithms developed for advanced single-molecule applications. There are different reasons for this, linked, e.g., to fluorophore aspecific interactions, brightness, photostability, blinking, and emission and excitation spectra. In particular, these spectra and the excitation source are interdependent, and the latter affects the autofluorescence of sample substrate, medium, and/or biological specimen. Here, we review these and other critical points for fluorophore selection in single-molecule microscopy. We also describe the possible kinds of fluorophores and the microscopy techniques based on single-molecule fluorescence. We explain the importance and impact of the various issues in fluorophore choice, and discuss how this can become more effective and decisive for increasingly demanding experiments in single- and multiple-color applications.
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6
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7
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Varga D, Majoros H, Ujfaludi Z, Erdélyi M, Pankotai T. Quantification of DNA damage induced repair focus formation via super-resolution dSTORM localization microscopy. NANOSCALE 2019; 11:14226-14236. [PMID: 31317161 DOI: 10.1039/c9nr03696b] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
In eukaryotic cells, each process, in which DNA is involved, should take place in the context of a chromatin structure. DNA double-strand breaks (DSBs) are one of the most deleterious lesions often leading to chromosomal rearrangement. In response to environmental stresses, cells have developed repair mechanisms to eliminate the DSBs. Upon DSB induction, several factors play roles in chromatin relaxation by catalysing the appropriate histone posttranslational modification (PTM) steps, therefore promoting the access of the repair factors to the DSBs. Among these PTMs, the phosphorylation of the histone variant H2AX at its Ser139 residue (also known as γH2AX) could be observed at the break sites. The structure of a DNA double-strand break induced repair focus has to be organized during the repair as it contributes to the accessibility of specific repair proteins to the damaged site. Our aim was to develop a quantitative approach to analyse the morphology of single repair foci by super-resolution dSTORM microscopy to gain insight into chromatin organization in DNA repair. We have established a specific dSTORM measurement process by developing a new analytical algorithm for gaining quantitative information about chromatin morphology and repair foci topology at an individual γH2AX enriched repair focus. Using this method we quantified single repair foci to show the distribution of γH2AX. The image of individual γH2AX referred to as the Single target Molecule response scatter Plot (SMPlot) was obtained by using high lateral resolution dSTORM images. Determination of the average localization numbers in an SMPlot was one of the key steps of quantitative dSTORM. A repair focus is made up of nanofoci. Such a substructure of repair foci can only be resolved and detected with super-resolution microscopy. Determination of the number of γH2AXs in the nanofoci was another key step of quantitative dSTORM. Additionally, based on our new analysis method, we were able to show the number of nucleosomes in each nanofocus that could allow us to define the possible chromatin structure and the nucleosome density around the break sites. This method is one of the first demonstrations of a single-cell based quantitative measurement of a discrete repair focus, which could provide new opportunities to categorize the spatial organization of nanofoci by parametric determination of topological similarity.
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Affiliation(s)
- Dániel Varga
- University of Szeged, Department of Optics and Quantum Electronics, Hungary.
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8
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Ye Z, Yu H, Yang W, Zheng Y, Li N, Bian H, Wang Z, Liu Q, Song Y, Zhang M, Xiao Y. Strategy to Lengthen the On-Time of Photochromic Rhodamine Spirolactam for Super-resolution Photoactivated Localization Microscopy. J Am Chem Soc 2019; 141:6527-6536. [PMID: 30938994 DOI: 10.1021/jacs.8b11369] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Rhodamine derivatives and analogues have been widely used for different super-resolution imaging techniques, including photoactivated localization microscopy (PALM). Among them, rhodamine spirolactams exhibit great superiority for PALM imaging due to a desirable bright-dark contrast during the photochromic switching process. Although considerable attention has been paid to the chemical modifications on rhodamine spirolactams, the on-time of photochromic switching, one of the key characteristics for PALM imaging, has never been optimized in previous developments. In this study, we proposed that simply installing a carboxyl group close to the lactam site could impose an intramolecular acidic environment, stabilize the photoactivated zwitterionic structure, and thus effectively increase the on-time. On the basis of this idea, we have synthesized a new rhodamine spirolactam, Rh-Gly, that demonstrated considerably longer on-time than the other tested analogues, as well as an enhancement of single-molecule brightness, an improvement on signal-to-noise ratio and an enlargement of total collected photons of a single molecule before photobleaching. Finally, super-resolution images of live cell mitochondria stained with Rh-Gly have been obtained with a good temporal resolution of 10 s, as well as a satisfactory localization precision of ∼25 nm. Through self-labeling protein tags, Rh-Gly modified with a HaloTag ligand enabled super-resolution imaging of histone H2B proteins in live HeLa cells; through immunostaining antibodies labeled with an isothiocyanate-substituted Rh-Gly, super-resolution imaging of microtubules was achieved in fixed cells. Therefore, our simple and effective strategy provides novel insight for developing further enhanced rhodamine spirolactams recommendable for PALM imaging.
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Affiliation(s)
- Zhiwei Ye
- College of Environmental Sciences , Liaoning University , Shenyang 110036 , People's Republic of China.,State Key Laboratory of Fine Chemicals , Dalian University of Technology , Dalian 116024 , People's Republic of China
| | - Haibo Yu
- College of Environmental Sciences , Liaoning University , Shenyang 110036 , People's Republic of China
| | - Wei Yang
- State Key Laboratory of Fine Chemicals , Dalian University of Technology , Dalian 116024 , People's Republic of China.,Chemical Analysis and Research Center , Dalian University of Technology , Dalian 116024 , People's Republic of China
| | - Ying Zheng
- State Key Laboratory of Fine Chemicals , Dalian University of Technology , Dalian 116024 , People's Republic of China
| | - Ning Li
- State Key Laboratory of Fine Chemicals , Dalian University of Technology , Dalian 116024 , People's Republic of China
| | - Hui Bian
- State Key Laboratory of Fine Chemicals , Dalian University of Technology , Dalian 116024 , People's Republic of China
| | - Zechen Wang
- College of Environmental Sciences , Liaoning University , Shenyang 110036 , People's Republic of China
| | - Qiang Liu
- College of Environmental Sciences , Liaoning University , Shenyang 110036 , People's Republic of China
| | - Youtao Song
- College of Environmental Sciences , Liaoning University , Shenyang 110036 , People's Republic of China
| | - Mingyan Zhang
- Liaoning Center of Disease Prevention and Control , Shenyang 110001 , People's Republic of China
| | - Yi Xiao
- State Key Laboratory of Fine Chemicals , Dalian University of Technology , Dalian 116024 , People's Republic of China
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9
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Halabi EA, Pinotsi D, Rivera-Fuentes P. Photoregulated fluxional fluorophores for live-cell super-resolution microscopy with no apparent photobleaching. Nat Commun 2019; 10:1232. [PMID: 30874551 PMCID: PMC6420572 DOI: 10.1038/s41467-019-09217-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 02/25/2019] [Indexed: 01/13/2023] Open
Abstract
Photoswitchable molecules have multiple applications in the physical and life sciences because their properties can be modulated with light. Fluxional molecules, which undergo rapid degenerate rearrangements in the electronic ground state, also exhibit switching behavior. The stochastic nature of fluxional switching, however, has hampered its application in the development of functional molecules and materials. Here we combine photoswitching and fluxionality to develop a fluorophore that enables very long (>30 min) time-lapse single-molecule localization microscopy in living cells with minimal phototoxicity and no apparent photobleaching. These long time-lapse experiments allow us to track intracellular organelles with unprecedented spatiotemporal resolution, revealing new information of the three-dimensional compartmentalization of synaptic vesicle trafficking in live human neurons. Super-resolution microscopy with spontaneously blinking dyes is dependent on pH and polarity of the medium. Here the authors introduce a photoactivatable fluxional fluorophore for live cell imaging that allows control over the fraction of spontaneously blinking molecules independently of medium properties.
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Affiliation(s)
- Elias A Halabi
- Laboratory of Organic Chemistry, ETH Zurich, Zurich, 8093, Switzerland
| | - Dorothea Pinotsi
- Scientific Center for Optical and Electron Microscopy, ETH Zurich, Zurich, 8093, Switzerland
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10
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Bittel AM, Saldivar IS, Dolman NJ, Nan X, Gibbs SL. Superresolution microscopy with novel BODIPY-based fluorophores. PLoS One 2018; 13:e0206104. [PMID: 30366346 PMCID: PMC6203453 DOI: 10.1371/journal.pone.0206104] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Accepted: 10/05/2018] [Indexed: 01/19/2023] Open
Abstract
Multicolor single-molecule localization microscopy (SMLM) expands our understanding of subcellular details and enables the study of biomolecular interactions through precise visualization of multiple molecules in a single sample with resolution of ~10–20 nm. Probe selection is vital to multicolor SMLM, as the fluorophores must not only exhibit minimal spectral crosstalk, but also be compatible with the same photochemical conditions that promote fluorophore photoswitching. While there are numerous commercially available photoswitchable fluorophores that are optimally excited in the standard Cy3 channel, they are restricted to short Stokes shifts (<30 nm), limiting the number of colors that can be resolved in a single sample. Furthermore, while imaging buffers have been thoroughly examined for commonly used fluorophore scaffolds including cyanine, rhodamine, and oxazine, optimal conditions have not been found for the BODIPY scaffold, precluding its routine use for multicolor SMLM. Herein, we screened common imaging buffer conditions including seven redox reagents with five additives, resulting in 35 overall imaging buffer conditions to identify compatible combinations for BODIPY-based fluorophores. We then demonstrated that novel, photoswitchable BODIPY-based fluorophores with varied length Stokes shifts provide additional color options for SMLM using a combination of BODIPY-based and commercially available photoswitchable fluorophores.
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Affiliation(s)
- Amy M. Bittel
- Biomedical Engineering Department, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Isaac S. Saldivar
- Biomedical Engineering Department, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Nick J. Dolman
- Thermo Fisher Scientific, Pittsburg, Pennsylvania, United States of America
| | - Xiaolin Nan
- Biomedical Engineering Department, Oregon Health & Science University, Portland, Oregon, United States of America
- Knight Cancer Institute, Oregon Health & Science University, Portland, Oregon, United States of America
- OHSU Center for Spatial Systems Biomedicine, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Summer L. Gibbs
- Biomedical Engineering Department, Oregon Health & Science University, Portland, Oregon, United States of America
- Knight Cancer Institute, Oregon Health & Science University, Portland, Oregon, United States of America
- OHSU Center for Spatial Systems Biomedicine, Oregon Health & Science University, Portland, Oregon, United States of America
- * E-mail:
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11
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Abstract
The past decade has witnessed an explosion in the use of super-resolution fluorescence microscopy methods in biology and other fields. Single-molecule localization microscopy (SMLM) is one of the most widespread of these methods and owes its success in large part to the ability to control the on-off state of fluorophores through various chemical, photochemical, or binding-unbinding mechanisms. We provide here a comprehensive overview of switchable fluorophores in SMLM including a detailed review of all major classes of SMLM fluorophores, and we also address strategies for labeling specimens, considerations for multichannel and live-cell imaging, potential pitfalls, and areas for future development.
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Affiliation(s)
- Honglin Li
- Department of Chemistry, University of Washington, Seattle, Washington, USA, 98195
| | - Joshua C. Vaughan
- Department of Chemistry, University of Washington, Seattle, Washington, USA, 98195
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington, USA, 98195
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12
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A Theoretical High-Density Nanoscopy Study Leads to the Design of UNLOC, a Parameter-free Algorithm. Biophys J 2018; 115:565-576. [PMID: 30029772 DOI: 10.1016/j.bpj.2018.06.024] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Revised: 05/17/2018] [Accepted: 06/27/2018] [Indexed: 11/23/2022] Open
Abstract
Single-molecule localization microscopy (SMLM) enables the production of high-resolution images by imaging spatially isolated fluorescent particles. Although challenging, the result of SMLM analysis lists the position of individual molecules, leading to a valuable quantification of the stoichiometry and spatial organization of molecular actors. Both the signal/noise ratio and the density (Dframe), i.e., the number of fluorescent particles per μm2 per frame, have previously been identified as determining factors for reaching a given SMLM precision. Establishing a comprehensive theoretical study relying on these two parameters is therefore of central interest to delineate the achievable limits for accurate SMLM observations. Our study reports that in absence of prior knowledge of the signal intensity α, the density effect on particle localization is more prominent than that anticipated from theoretical studies performed at known α. A first limit appears when, under a low-density hypothesis (i.e., one-Gaussian fitting hypothesis), any fluorescent particle distant by less than ∼600 nm from the particle of interest biases its localization. In fact, all particles should be accounted for, even those dimly fluorescent, to ascertain unbiased localization of any surrounding particles. Moreover, even under a high-density hypothesis (i.e., multi-Gaussian fitting hypothesis), a second limit arises because of the impossible distinction of particles located too closely. An increase in Dframe is thus likely to deteriorate the localization precision, the image reconstruction, and more generally the quantification accuracy. Our study firstly provides a density-signal/noise ratio space diagram for use as a guide in data recording toward reaching an achievable SMLM resolution. Additionally, it leads to the identification of the essential requirements for implementing UNLOC, a parameter-free and fast computing algorithm approaching the Cramér-Rao bound for particles at high-density per frame and without any prior knowledge of their intensity. UNLOC is available as an ImageJ plugin.
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13
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Thédié D, Berardozzi R, Adam V, Bourgeois D. Photoswitching of Green mEos2 by Intense 561 nm Light Perturbs Efficient Green-to-Red Photoconversion in Localization Microscopy. J Phys Chem Lett 2017; 8:4424-4430. [PMID: 28850784 DOI: 10.1021/acs.jpclett.7b01701] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Green-to-red photoconvertible fluorescent proteins (PCFPs) such as mEos2 and its derivatives are widely used in PhotoActivated Localization Microscopy (PALM). However, the complex photophysics of these genetically encoded markers complicates the quantitative analysis of PALM data. Here, we show that intense 561 nm light (∼1 kW/cm2) typically used to localize single red molecules considerably affects the green-state photophysics of mEos2 by populating at least two reversible dark states. These dark states retard green-to-red photoconversion through a shelving effect, although one of them is rapidly depopulated by 405 nm light illumination. Multiple mEos2 switching and irreversible photobleaching is thus induced by yellow/green and violet photons before green-to-red photoconversion occurs, contributing to explain the apparent limited signaling efficiency of this PCFP. Our data reveals that the photophysics of PCFPs of anthozoan origin is substantially more complex than previously thought, and suggests that intense 561 nm laser light should be used with care, notably for quantitative or fast PALM approaches.
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Affiliation(s)
- Daniel Thédié
- Institut de Biologie Structurale, CNRS, Université Grenoble Alpes, CEA, IBS, 38044 Grenoble, France
| | - Romain Berardozzi
- Institut de Biologie Structurale, CNRS, Université Grenoble Alpes, CEA, IBS, 38044 Grenoble, France
| | - Virgile Adam
- Institut de Biologie Structurale, CNRS, Université Grenoble Alpes, CEA, IBS, 38044 Grenoble, France
| | - Dominique Bourgeois
- Institut de Biologie Structurale, CNRS, Université Grenoble Alpes, CEA, IBS, 38044 Grenoble, France
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14
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Jenkinson DR, Cadby AJ, Jones S. The Synthesis and Photophysical Analysis of a Series of 4-Nitrobenzochalcogenadiazoles for Super-Resolution Microscopy. Chemistry 2017; 23:12585-12592. [PMID: 28703339 DOI: 10.1002/chem.201702289] [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] [Received: 05/19/2017] [Indexed: 11/07/2022]
Abstract
A series of 4-nitrobenzodiazoles with atomic substitution through the chalcogen group were synthesised and their photophysical properties analysed with a view for use in single-molecule localisation microscopy. Sub-diffraction resolution imaging was achieved for silica nanoparticles coated with each dye. Those containing larger atoms were favoured for super-resolution microscopy due to a reduced blink rate (required for stochastic events to be localised). The sulfur-containing molecule was deemed most amenable for widespread use due to the ease of synthetic manipulation compared to the selenium-containing derivative.
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Affiliation(s)
- Daniel Ray Jenkinson
- Department of Chemistry, University of Sheffield, Dainton Building, Brook Hill, Sheffield, S3 7HF, UK.,Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK
| | - Ashley James Cadby
- Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK
| | - Simon Jones
- Department of Chemistry, University of Sheffield, Dainton Building, Brook Hill, Sheffield, S3 7HF, UK
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