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Barulin A, Wenger J. Ultraviolet Photostability Improvement for Autofluorescence Correlation Spectroscopy on Label-Free Proteins. J Phys Chem Lett 2020; 11:2027-2035. [PMID: 32083877 DOI: 10.1021/acs.jpclett.0c00209] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The poor photostability and low brightness of protein autofluorescence have been major limitations preventing the detection of label-free proteins at the single-molecule level. Overcoming these issues, we report here a strategy to promote the photostability of proteins and use their natural tryptophan autofluorescence in the ultraviolet (UV) for fluorescence correlation spectroscopy (FCS). Combining enzymatic oxygen scavengers with antioxidants and triplet-state quenchers greatly promotes the protein photostability, reduces the photobleaching probability, and improves the net autofluorescence detection rate. Our results show that the underlying photochemical concepts initially derived for organic visible fluorescent dyes are quite general. Using this approach, we achieved UV fluorescence correlation spectroscopy on label-free streptavidin proteins containing only 24 tryptophan residues, 6.5× fewer than the current state-of-the-art. This strategy greatly extends the possibility of detecting single label-free proteins with the versatility of single-molecule fluorescence without requiring the presence of a potentially disturbing external fluorescent marker. It also opens new perspectives to improve the UV durability of organic devices.
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Affiliation(s)
- Aleksandr Barulin
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, 13013 Marseille, France
| | - Jérôme Wenger
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, 13013 Marseille, France
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Barulin A, Claude JB, Patra S, Bonod N, Wenger J. Deep Ultraviolet Plasmonic Enhancement of Single Protein Autofluorescence in Zero-Mode Waveguides. NANO LETTERS 2019; 19:7434-7442. [PMID: 31526002 DOI: 10.1021/acs.nanolett.9b03137] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Single molecule detection provides detailed information about molecular structures and functions but it generally requires the presence of a fluorescent marker which can interfere with the activity of the target molecule or complicate the sample production. Detecting a single protein with its natural UV autofluorescence is an attractive approach to avoid all the issues related to fluorescence labeling. However, the UV autofluorescence signal from a single protein is generally extremely weak. Here, we use aluminum plasmonics to enhance the tryptophan autofluorescence emission of single proteins in the UV range. Zero-mode waveguide nanoapertures enable the observation of the UV fluorescence of single label-free β-galactosidase proteins with increased brightness, microsecond transit times, and operation at micromolar concentrations. We demonstrate quantitative measurements of the local concentration, diffusion coefficient, and hydrodynamic radius of the label-free protein over a broad range of zero-mode waveguide diameters. Although the plasmonic fluorescence enhancement has generated a tremendous interest in the visible and near-infrared parts of the spectrum, this work pushes further the limits of plasmonic-enhanced single molecule detection into the UV range and constitutes a major step forward in our ability to interrogate single proteins in their native state at physiological concentrations.
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Affiliation(s)
- Aleksandr Barulin
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel , 13013 Marseille , France
| | - Jean-Benoît Claude
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel , 13013 Marseille , France
| | - Satyajit Patra
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel , 13013 Marseille , France
| | - Nicolas Bonod
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel , 13013 Marseille , France
| | - Jérôme Wenger
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel , 13013 Marseille , France
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Nobis D, Fisher RS, Simmermacher M, Hopkins PA, Tor Y, Jones AC, Magennis SW. Single-Molecule Detection of a Fluorescent Nucleobase Analogue via Multiphoton Excitation. J Phys Chem Lett 2019; 10:5008-5012. [PMID: 31397575 PMCID: PMC7024020 DOI: 10.1021/acs.jpclett.9b02108] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The ability to routinely detect fluorescent nucleobase analogues at the single-molecule level would create a wealth of opportunities to study nucleic acids. We report the multiphoton-induced fluorescence and single-molecule detection of a dimethylamine-substituted extended-6-aza-uridine (DMAthaU). We show that DMAthaU can exist in a highly fluorescent form, emitting strongly in the visible region (470-560 nm). Using pulse-shaped broadband Ti:sapphire laser excitation, DMAthaU undergoes two-photon (2P) absorption at low excitation powers, switching to three-photon (3P) absorption at high incident intensity. The assignment of a 3P process is supported by cubic response calculations. Under both 2P and 3P excitation, the single-molecule brightness was over an order of magnitude higher than reported previously for any fluorescent base analogue, which facilitated the first single-molecule detection of an emissive nucleoside with multiphoton excitation.
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Affiliation(s)
- David Nobis
- WestCHEM School of Chemistry, University of Glasgow, Joseph Black Building, University Avenue, Glasgow G12 8QQ, U.K
| | - Rachel S. Fisher
- EaStCHEM School of Chemistry, The University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
| | - Mats Simmermacher
- EaStCHEM School of Chemistry, The University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
| | - Patrycja A. Hopkins
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Yitzhak Tor
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Anita C. Jones
- EaStCHEM School of Chemistry, The University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
- Corresponding Authors (A.C.J.)., (S.W.M.)
| | - Steven W. Magennis
- WestCHEM School of Chemistry, University of Glasgow, Joseph Black Building, University Avenue, Glasgow G12 8QQ, U.K
- Corresponding Authors (A.C.J.)., (S.W.M.)
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Fisher RS, Nobis D, Füchtbauer AF, Bood M, Grøtli M, Wilhelmsson LM, Jones AC, Magennis SW. Pulse-shaped two-photon excitation of a fluorescent base analogue approaches single-molecule sensitivity. Phys Chem Chem Phys 2018; 20:28487-28498. [PMID: 30412214 DOI: 10.1039/c8cp05496g] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Fluorescent nucleobase analogues (FBAs) have many desirable features in comparison to extrinsic fluorescent labels, but they are yet to find application in ultrasensitive detection. Many of the disadvantages of FBAs arise from their short excitation wavelengths (often in the ultraviolet), making two-photon excitation a potentially attractive approach. Pentacyclic adenine (pA) is a recently developed FBA that has an exceptionally high two-photon brightness. We have studied the two-photon-excited fluorescence properties of pA and how they are affected by incorporation in DNA. We find that pA is more photostable under two-photon excitation than via resonant absorption. When incorporated in an oligonucleotide, pA has a high two-photon cross section and emission quantum yield, varying with sequence context, resulting in the highest reported brightness for such a probe. The use of a two-photon microscope with ultrafast excitation and pulse shaping has allowed the detection of pA-containing oligonucleotides in solution with a limit of detection of ∼5 molecules, demonstrating that practical single-molecule detection of FBAs is now within reach.
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Affiliation(s)
- Rachel S Fisher
- EaStCHEM School of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, UK.
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Lane RSK, Jones R, Sinkeldam RW, Tor Y, Magennis SW. Two-photon-induced fluorescence of isomorphic nucleobase analogs. Chemphyschem 2014; 15:867-71. [PMID: 24604669 DOI: 10.1002/cphc.201400031] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2014] [Indexed: 11/06/2022]
Abstract
Five isomorphic fluorescent uridine mimics have been subjected to two-photon (2P) excitation analysis to investigate their potential applicability as non-perturbing probes for the single-molecule detection of nucleic acids. We find that small structural differences can cause major changes in the 2P excitation probability, with the 2P cross sections varying by over one order of magnitude. Two of the probes, both thiophene-modified uridine analogs, have the highest 2P cross sections (3.8 GM and 7.6 GM) reported for nucleobase analogs, using a conventional Ti:sapphire laser for excitation at 690 nm; they also have the lowest emission quantum yields. In contrast, the analogs with the highest reported quantum yields have the lowest 2P cross sections. The structure-photophysical property relationship presented here is a first step towards the rational design of emissive nucleobase analogs with controlled 2P characteristics. The results demonstrate the potential for major improvements through judicious structural modifications.
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Affiliation(s)
- Richard S K Lane
- School of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL (UK)
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Lane RSK, Magennis SW. Two-photon excitation of the fluorescent nucleobase analogues 2-AP and tC. RSC Adv 2012. [DOI: 10.1039/c2ra21881j] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
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Electrostatic interactions of fluorescent molecules with dielectric interfaces studied by total internal reflection fluorescence correlation spectroscopy. Int J Mol Sci 2010; 11:386-406. [PMID: 20386645 PMCID: PMC2852845 DOI: 10.3390/ijms11020386] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Revised: 01/17/2010] [Accepted: 01/21/2010] [Indexed: 01/24/2023] Open
Abstract
Electrostatic interactions between dielectric surfaces and different fluorophores used in ultrasensitive fluorescence microscopy are investigated using objective-based Total Internal Reflection Fluorescence Correlation Spectroscopy (TIR-FCS). The interfacial dynamics of cationic rhodamine 123 and rhodamine 6G, anionic/dianionic fluorescein, zwitterionic rhodamine 110 and neutral ATTO 488 are monitored at various ionic strengths at physiological pH. As analyzed by means of the amplitude and time-evolution of the autocorrelation function, the fluorescent molecules experience electrostatic attraction or repulsion at the glass surface depending on their charges. Influences of the electrostatic interactions are also monitored through the triplet-state population and triplet relaxation time, including the amount of detected fluorescence or the count-rate-per-molecule parameter. These TIR-FCS results provide an increased understanding of how fluorophores are influenced by the microenvironment of a glass surface, and show a promising approach for characterizing electrostatic interactions at interfaces.
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Sahoo B, Balaji J, Nag S, Kaushalya SK, Maiti S. Protein aggregation probed by two-photon fluorescence correlation spectroscopy of native tryptophan. J Chem Phys 2009; 129:075103. [PMID: 19044804 DOI: 10.1063/1.2969110] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Fluorescence correlation spectroscopy (FCS) has proven to be a powerful tool for the study of a range of biophysical problems including protein aggregation. However, the requirement of fluorescent labeling has been a major drawback of this approach. Here we show that the intrinsic tryptophan fluorescence, excited via a two-photon mechanism, can be effectively used to study the aggregation of tryptophan containing proteins by FCS. This method can also yield the tryptophan fluorescence lifetime in parallel, which provides a complementary parameter to understand the aggregation process. We demonstrate that the formation of soluble aggregates of barstar at pH 3.5 shows clear signatures both in the two-photon tryptophan FCS data and in the tryptophan lifetime analysis. The ability to probe the soluble aggregates of unmodified proteins is significant, given the major role played by this species in amyloid toxicity.
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Affiliation(s)
- Bankanidhi Sahoo
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
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Li Q, Seeger S. Label-free detection of single protein molecules using deep UV fluorescence lifetime microscopy. Anal Chem 2007; 78:2732-7. [PMID: 16615786 DOI: 10.1021/ac052166u] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We present the detection of single beta-galactosidase molecules from Escherichia coli (Ecbeta Gal) using deep UV laser-based fluorescence lifetime microscopy. The native fluorescence from intrinsic tryptophan emission has been observed after one-photon excitation at 266 nm. Applying the time-resolved single-photon counting method, we investigated the fluorescence lifetime distribution and the bursts of autofluorescence photons from tryptophan residues in Ecbeta Gal protein as well as fluorescence correlation spectroscopy of Ecbeta Gal. The results demonstrate that deep UV laser-based fluorescence lifetime microscopy is useful for identification of biological macromolecules at the single-molecule level using intrinsic fluorescence.
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Affiliation(s)
- Qiang Li
- Physikalisch-Chemisches Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
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Katilius E, Woodbury NW. Multiphoton excitation of fluorescent DNA base analogs. JOURNAL OF BIOMEDICAL OPTICS 2006; 11:044004. [PMID: 16965161 DOI: 10.1117/1.2337521] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Multiphoton excitation was used to investigate properties of the fluorescent DNA base analogs, 2-aminopurine (2AP) and 6-methylisoxanthopterin (6MI). 2-aminopurine, a fluorescent analog of adenine, was excited by three-photon absorption. Fluorescence correlation measurements were attempted to evaluate the feasibility of using three-photon excitation of 2AP for DNA-protein interaction studies. However, high excitation power and long integration times needed to acquire high signal-to-noise fluorescence correlation curves render three-photon excitation FCS of 2AP not very useful for studying DNA base dynamics. The fluorescence properties of 6-methylisoxanthopterin, a guanine analog, were investigated using two-photon excitation. The two-photon absorption cross-section of 6MI was estimated to be about 2.5 x 10(-50) cm(4)s (2.5 GM units) at 700 nm. The two-photon excitation spectrum was measured in the spectral region from 700 to 780 nm; in this region the shape of the two-photon excitation spectrum is very similar to the shape of single-photon excitation spectrum in the near-UV spectral region. Two-photon excitation of 6MI is suitable for fluorescence correlation measurements. Such measurements can be used to study DNA base dynamics and DNA-protein interactions over a broad range of time scales.
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Affiliation(s)
- Evaldas Katilius
- Arizona State University, Biodesign Institute, Department of Chemistry and Biochemistry and the Center for BioOptical Nanotechnology, Tempe, Arizona 85287-5201, USA.
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Eggeling C, Volkmer A, Seidel CAM. Molecular photobleaching kinetics of Rhodamine 6G by one- and two-photon induced confocal fluorescence microscopy. Chemphyschem 2006; 6:791-804. [PMID: 15884061 DOI: 10.1002/cphc.200400509] [Citation(s) in RCA: 207] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Under high-excitation irradiance conditions in one- and two-photon induced fluorescence microscopy, the photostability of fluorescent dyes is of crucial importance for the detection sensitivity of single molecules and for the contrast in fluorescence imaging. Herein, we report on the dependence of photobleaching on the excitation conditions, using the dye Rhodamine 6G as a typical example. The different excitation modes investigated include 1) one-photon excitation into the first-excited singlet state in the range of 500 to 528 nm by continuous wave and picosecond-pulsed lasers and 2) two- and one-photon excitation to higher-excited singlet states at 800 and 350 nm, respectively, by femtosecond pulses. Experimental strategies are presented, which allow resolving the photophysics. From single-molecule trajectories and fluorescence correlation spectroscopy, as well as with a simple theoretical model based on steady-state solutions of molecular rate equation analysis, we determined the underlying photobleaching mechanisms and quantified the photokinetic parameters describing the dependence of the fluorescence signal on the excitation irradiance. The comparison with experimental data and an exact theoretical model show that only minor deviations between the different theoretical approaches can be observed for high-pulsed excitation irradiances. It is shown that fluorescence excitation is in all cases limited by photolysis from higher-excited electronic states. In contrast to picosecond-pulsed excitation, this is extremely severe for both one- and two-photon excitation with femtosecond pulses. Furthermore, the photostability of the higher-excited electronic states is strongly influenced by environmental conditions, such as polarity and temperature.
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Affiliation(s)
- Christian Eggeling
- Max-Planck-Institute for Biophysical Chemistry, Department of Nanobiophotonics, Am Fassberg 11, 37077 Göttingen, Germany.
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Sanabia JE, Goldner LS, Lacaze PA, Hawkins ME. On the Feasibility of Single-Molecule Detection of the Guanosine-Analogue 3-MI. J Phys Chem B 2004. [DOI: 10.1021/jp049901a] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jason E. Sanabia
- Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 and Pediatric Oncology Branch, National Cancer Institute, Bethesda, Maryland 20892
| | - Lori S. Goldner
- Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 and Pediatric Oncology Branch, National Cancer Institute, Bethesda, Maryland 20892
| | - Pierre-Antoine Lacaze
- Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 and Pediatric Oncology Branch, National Cancer Institute, Bethesda, Maryland 20892
| | - Mary E. Hawkins
- Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 and Pediatric Oncology Branch, National Cancer Institute, Bethesda, Maryland 20892
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Li Q, Ruckstuhl T, Seeger S. Deep-UV Laser-Based Fluorescence Lifetime Imaging Microscopy of Single Molecules. J Phys Chem B 2004. [DOI: 10.1021/jp0375160] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Qiang Li
- Physikalisch-Chemisches Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
| | - Thomas Ruckstuhl
- Physikalisch-Chemisches Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
| | - Stefan Seeger
- Physikalisch-Chemisches Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
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Lippitz M, Erker W, Decker H, van Holde KE, Basché T. Two-photon excitation microscopy of tryptophan-containing proteins. Proc Natl Acad Sci U S A 2002; 99:2772-7. [PMID: 11880629 PMCID: PMC122423 DOI: 10.1073/pnas.052662999] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have examined the feasibility of observing single protein molecules by means of their intrinsic tryptophan emission after two-photon excitation. A respiratory protein from spiders, the 24-meric hemocyanin, containing 148 tryptophans, was studied in its native state under almost in vivo conditions. In this specific case, the intensity of the tryptophan emission signals the oxygen load, allowing one to investigate molecular cooperativity. As a system with even higher tryptophan content, we also investigated latex spheres covered with the protein avidin, resulting in 340 tryptophans per sphere. The ratio of the fluorescence quantum efficiency to the bleaching efficiency was found to vary between 2 and 180 after two-photon excitation for tryptophan free in buffer solution, in hemocyanin, and in avidin-coated spheres. In the case of hemocyanin, this ratio leads to about four photons detected before photobleaching. Although this number is quite small, the diffusion of individual protein molecules could be detected by fluorescence correlation spectroscopy. In avidin-coated spheres, the tryptophans exhibit a higher photostability, so that even imaging of single spheres becomes possible. As an unexpected result of the measurements, it was discovered that the population of the oxygenated state of hemocyanin can be changed by means of a one-photon process with the same laser source that monitors this population in a two-photon process.
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Affiliation(s)
- M Lippitz
- Institute of Physical Chemistry, Jakob-Welder-Weg 11, and Institute of Molecular Biophysics, Jakob-Welder-Weg 26, University of Mainz, 55099 Mainz, Germany
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