1
|
Barroso M, Monaghan MG, Niesner R, Dmitriev RI. Probing organoid metabolism using fluorescence lifetime imaging microscopy (FLIM): The next frontier of drug discovery and disease understanding. Adv Drug Deliv Rev 2023; 201:115081. [PMID: 37647987 PMCID: PMC10543546 DOI: 10.1016/j.addr.2023.115081] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Revised: 04/20/2023] [Accepted: 08/24/2023] [Indexed: 09/01/2023]
Abstract
Organoid models have been used to address important questions in developmental and cancer biology, tissue repair, advanced modelling of disease and therapies, among other bioengineering applications. Such 3D microenvironmental models can investigate the regulation of cell metabolism, and provide key insights into the mechanisms at the basis of cell growth, differentiation, communication, interactions with the environment and cell death. Their accessibility and complexity, based on 3D spatial and temporal heterogeneity, make organoids suitable for the application of novel, dynamic imaging microscopy methods, such as fluorescence lifetime imaging microscopy (FLIM) and related decay time-assessing readouts. Several biomarkers and assays have been proposed to study cell metabolism by FLIM in various organoid models. Herein, we present an expert-opinion discussion on the principles of FLIM and PLIM, instrumentation and data collection and analysis protocols, and general and emerging biosensor-based approaches, to highlight the pioneering work being performed in this field.
Collapse
Affiliation(s)
- Margarida Barroso
- Department of Molecular and Cellular Physiology, Albany Medical College, Albany, NY 12208, USA
| | - Michael G Monaghan
- Department of Mechanical, Manufacturing and Biomedical Engineering, Trinity College Dublin, Dublin 02, Ireland
| | - Raluca Niesner
- Dynamic and Functional In Vivo Imaging, Freie Universität Berlin and Biophysical Analytics, German Rheumatism Research Center, Berlin, Germany
| | - Ruslan I Dmitriev
- Tissue Engineering and Biomaterials Group, Department of Human Structure and Repair, Faculty of Medicine and Health Sciences, Ghent University, C. Heymanslaan 10, 9000 Ghent, Belgium; Ghent Light Microscopy Core, Ghent University, 9000 Ghent, Belgium.
| |
Collapse
|
2
|
Li H, Cao S, Zhang S, Chen J, Xu J, Knutson JR. Ultrafast Förster resonance energy transfer from tyrosine to tryptophan in monellin: potential intrinsic spectroscopic ruler. Phys Chem Chem Phys 2023; 25:7239-7250. [PMID: 36853740 DOI: 10.1039/d2cp05842a] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023]
Abstract
Ultrafast Förster Resonance Energy Transfer (FRET) between tyrosine (Tyr) and tryptophan (Trp) residues in the protein monellin has been investigated using picosecond and femtosecond time-resolved fluorescence spectroscopy. Decay associated spectra (DAS) and time-resolved emission spectra (TRES) taken with the different excitation wavelengths of 275, 290 and 295 nm were constructed via global analysis. At two of those three excitation loci (275 and 290 nm), earmarks of energy transfer from Tyr to Trp in monellin are seen, and particularly when the excitation is 275 nm, the energy transfer between Tyr and Trp clearly changes the signature emission DAS shape to that indicating excited state reaction (especially on the red side of fluorescence emission, near 380 nm). Those FRET signatures may overlap with the conventional signatory DAS in heterogeneous systems. When overlap and addition occur between FRET type DAS and "full positive" QSSQ (quasi-static self-quenching), mixed DAS shapes will emerge that still show "positive blue side and negative red sides", just with zero crossing shifted. In addition, excitation decay associated spectra (EDAS) taken with the different emission wavelengths of 330, 350 and 370 nm were constructed. In the study of protein dynamics, ultrafast FRET between Tyr and Trp could provide a basis for an intrinsic (non-perturbing) "spectroscopic ruler", potentially a powerful tool to detect even slight changes in protein structures.
Collapse
Affiliation(s)
- Haoyang Li
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Simin Cao
- Key Laboratory of 3D Micro/Nano Fabrication and Characterization of Zhejiang Province, School of Engineering, Westlake University, Hangzhou 310024, China
| | - Sanjun Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Jinquan Chen
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Jianhua Xu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Jay R Knutson
- Laboratory of Advanced Microscopy & Biophotonics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
| |
Collapse
|
3
|
Li H, Cao S, Chen J, Zhang S, Xu J, Knutson JR. Ultrafast fluorescence dynamics of NADH in aprotic solvents: Quasi-static self-quenching unmasked. J Photochem Photobiol A Chem 2023. [DOI: 10.1016/j.jphotochem.2022.114384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
|
4
|
Determination of fluorescence quantum yields and decay times of NADH and FAD in water-alcohol mixtures: The analysis of radiative and nonradiative relaxation pathways. J Photochem Photobiol A Chem 2022. [DOI: 10.1016/j.jphotochem.2022.114388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
|
5
|
Li H, Jiang G, Jia M, Cao S, Zhang S, Chen J, Sun H, Xu J, Knutson JR. Ultrafast Förster resonance energy transfer between tyrosine and tryptophan: potential contributions to protein-water dynamics measurements. Phys Chem Chem Phys 2022; 24:18055-18066. [PMID: 35861343 DOI: 10.1039/d2cp02139k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Ultrafast Förster Resonance Energy Transfer (FRET) between Tyrosine (Tyr, Y) and Tryptophan (Trp, W) in the model peptides Trp-(Pro)n-Tyr (WPnY) has been investigated using a femtosecond up-conversion spectrophotofluorometer. The ultrafast energy transfer process (<100 ps) in short peptides (WY, WPY and WP2Y) has been resolved. In fact, this FRET rate is found to be mixed with the rates of solvent relaxation (SR), ultrafast population decay (QSSQ) and other lifetime components. To further dissect and analyze the FRET, a spectral working model is constructed, and the contribution of a FRET lifetime is separated by reconciling the shapes of decay associated spectra (DAS). Surprisingly, FRET efficiency did not decrease monotonically with the growth of the peptide chain (as expected) but increased first and then decreased. The highest FRET efficiency occurred in peptide WPY. The kinetic results have been accompanied with molecular dynamics simulations that reconcile and explain this strange phenomenon: due to the strong interaction between amino acids, the distance between the donor and receptor in peptide WPY is actually closest, resulting in the fastest FRET. In addition, the FRET lifetimes (τcal) were estimated within the molecular dynamics simulations, and they were consistent with the lifetimes (τexp) separated out by the experimental measurements and the DAS working model. This benchmark study has implications for both previous and future studies of protein ultrafast dynamics. The approach taken can be generalized for the study of proximate tyrosine and tryptophan in proteins and it suggests spectral strategies for extracting mixed rates in other complex FRET problems.
Collapse
Affiliation(s)
- Haoyang Li
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Guanyu Jiang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Menghui Jia
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Simin Cao
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Sanjun Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Jinquan Chen
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Haitao Sun
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Jianhua Xu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
| | - Jay R Knutson
- Laboratory of Advanced Microscopy & Biophotonics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
| |
Collapse
|
6
|
Gorbunova IA, Sasin ME, Golyshev DP, Semenov AA, Smolin AG, Beltukov YM, Vasyutinskii OS. Two-Photon Excited Fluorescence Dynamics in Enzyme-Bound NADH: the Heterogeneity of Fluorescence Decay Times and Anisotropic Relaxation. J Phys Chem B 2021; 125:9692-9707. [PMID: 34410128 DOI: 10.1021/acs.jpcb.1c04226] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The dynamics of polarized fluorescence in NADH in alcohol dehydrogenase (ADH) in buffer solution has been studied using the TCSPC spectroscopy. A global fit procedure was used for determination of the fluorescence parameters from experiment. The interpretation of the results obtained was supported by ab initio calculations of the NADH structure. A theoretical model was developed describing the polarized fluorescence decay in ADH-NADH complexes that considered several interaction scenarios. A comparative analysis of the polarization-insensitive fluorescence decay using multiexponential fitting models has been carried out. As shown, the origin of a significant enhancement of the decay time in the ADH-NADH complex can be attributed to the decrease of nonradiative relaxation rates in the nicotinamide ring in the conditions of the apolar binding site environment. The existence of a single decay time in the ADH-NADH complex in comparison with two decay times observed in free NADH was attributed to a single NADH unfolded conformation in the ADH binding site. Comparison of the experimental data with the theoretical model suggested the existence of an anisotropic relaxation time of about 1 ns that is related with the rotation of fluorescence transition dipole moment due to the rearrangement of the excited state NADH nuclear configuration.
Collapse
Affiliation(s)
| | - Maxim E Sasin
- Ioffe Institute, 26 Polytekhnicheskaya, St. Petersburg, 194021, Russia
| | - Dmitrii P Golyshev
- Ioffe Institute, 26 Polytekhnicheskaya, St. Petersburg, 194021, Russia.,Peter the Great St.Petersburg Polytechnic University, 29 Polytechnicheskaya, St. Petersburg, 195251, Russia
| | | | - Andrey G Smolin
- Ioffe Institute, 26 Polytekhnicheskaya, St. Petersburg, 194021, Russia
| | | | | |
Collapse
|
7
|
Cao S, Li H, Zhao Z, Zhang S, Chen J, Xu J, Knutson JR, Brand L. Ultrafast Fluorescence Spectroscopy via Upconversion and Its Applications in Biophysics. Molecules 2021; 26:molecules26010211. [PMID: 33401638 PMCID: PMC7794851 DOI: 10.3390/molecules26010211] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Revised: 12/23/2020] [Accepted: 12/23/2020] [Indexed: 11/25/2022] Open
Abstract
In this review, the experimental set-up and functional characteristics of single-wavelength and broad-band femtosecond upconversion spectrophotofluorometers developed in our laboratory are described. We discuss applications of this technique to biophysical problems, such as ultrafast fluorescence quenching and solvation dynamics of tryptophan, peptides, proteins, reduced nicotinamide adenine dinucleotide (NADH), and nucleic acids. In the tryptophan dynamics field, especially for proteins, two types of solvation dynamics on different time scales have been well explored: ~1 ps for bulk water, and tens of picoseconds for “biological water”, a term that combines effects of water and macromolecule dynamics. In addition, some proteins also show quasi-static self-quenching (QSSQ) phenomena. Interestingly, in our more recent work, we also find that similar mixtures of quenching and solvation dynamics occur for the metabolic cofactor NADH. In this review, we add a brief overview of the emerging development of fluorescent RNA aptamers and their potential application to live cell imaging, while noting how ultrafast measurement may speed their optimization.
Collapse
Affiliation(s)
- Simin Cao
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China; (S.C.); (H.L.); (Z.Z.); (S.Z.); (J.C.)
| | - Haoyang Li
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China; (S.C.); (H.L.); (Z.Z.); (S.Z.); (J.C.)
| | - Zenan Zhao
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China; (S.C.); (H.L.); (Z.Z.); (S.Z.); (J.C.)
| | - Sanjun Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China; (S.C.); (H.L.); (Z.Z.); (S.Z.); (J.C.)
| | - Jinquan Chen
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China; (S.C.); (H.L.); (Z.Z.); (S.Z.); (J.C.)
| | - Jianhua Xu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China; (S.C.); (H.L.); (Z.Z.); (S.Z.); (J.C.)
- Correspondence: (J.X.); (J.R.K.); Tel.: +86-21-6223-3936 (J.X.); +1-301-496-2557 (J.R.K.)
| | - Jay R. Knutson
- Laboratory for Advanced Microscopy and Biophotonics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
- Correspondence: (J.X.); (J.R.K.); Tel.: +86-21-6223-3936 (J.X.); +1-301-496-2557 (J.R.K.)
| | - Ludwig Brand
- Department of Biology, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA;
| |
Collapse
|
8
|
Gorbunova IA, Sasin ME, Beltukov YM, Semenov AA, Vasyutinskii OS. Anisotropic relaxation in NADH excited states studied by polarization-modulation pump-probe transient spectroscopy. Phys Chem Chem Phys 2020; 22:18155-18168. [PMID: 32766648 DOI: 10.1039/d0cp02496a] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
We present the results of experimental and theoretical studies of fast anisotropic relaxation and rotational diffusion in the first electron excited state of biological coenzyme NADH in water-ethanol solutions. The experiments have been carried out by means of a novel polarization-modulation transient method and fluorescence polarization spectroscopy. For interpretation of the experimental results a model of the anisotropic relaxation in terms of scalar and vector properties of transition dipole moments has been developed based on the Born-Oppenheimer approximation. This model allows for the description of fast isotropic and anisotropic excited state relaxation under excitation of molecules by ultrafast laser pulses in transient absorption and upconversion experiments. The results obtained suggest that the dynamics of anisotropic rovibronic relaxation in NADH under excitation with 100 fs pump laser pulses can be characterised by a single vibrational relaxation time τv lying in the range of 2-15 ps and a single rotation diffusion time τr lying in the range of 100-450 ps, both depending on ethanol concentration. The dependence of the times τv and τr on the solution polarity (static permittivity) and viscosity has been determined and analyzed. Limiting values of the term P2(cos θ) describing the rotation of the transition dipole moment in the course of vibrational relaxation have been determined from experiments as a function of ethanol concentration and analyzed.
Collapse
Affiliation(s)
| | - Maxim E Sasin
- Ioffe Institute, Polytekhnicheskaya 26, St. Petersburg, Russia.
| | | | | | | |
Collapse
|
9
|
Gorbunova IA, Sasin ME, Rubayo-Soneira J, Smolin AG, Vasyutinskii OS. Two-Photon Excited Fluorescence Dynamics in NADH in Water-Methanol Solutions: The Role of Conformation States. J Phys Chem B 2020; 124:10682-10697. [PMID: 33175534 DOI: 10.1021/acs.jpcb.0c07620] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The dynamics of polarized fluorescence in reduced nicotinamide adenine dinucleotide (NADH) at 460 nm under two-photon excitation at 720 nm by femtosecond laser pulses in water-methanol solutions has been studied experimentally and theoretically as a function of methanol concentration. A number of fluorescence parameters have been determined from experiment by means of the global fit procedure and then compared with the results reported by other authors. A comprehensive analysis of experimental errors was made. Ab initio calculations of the structure of NADH in water and methanol and of β-nicotinamide mononucleotide (NMNH) in vacuum have been carried out for clarifying the role of decay time heterogeneity. The main results obtained are as follows. An explanation of the heterogeneity in the measured fluorescence decay times in NADH has been suggested based on the influence of the internal molecular electric field in the nicotinamide ring on nonradiative decay rates. We suggest that different charge distributions in the cis and trans configurations result in different internal electrostatic field distributions that lead to the decay time heterogeneity. A slight but noticeable rise of the fluorescence decay times τ1 and τ2 with methanol concentration was observed and treated as a minor effect of a nonradiative relaxation slowing due to the decrease in solution polarity. Relative concentrations of the folded and unfolded NADH conformations in solutions have been determined using a new method of analysis of the rotational diffusion time τr as a function of methanol concentration on the basis of the Stokes-Einstein-Debye equation. The analysis of the fluorescence anisotropy parameters obtained under linearly and circularly polarized excitation and the parameter Ω has been carried out and resulted in the determination of the two-photon excitation tensor components and suggested the existence of two excitation channels with comparable intensities. These were the longitudinal excitation channel dominated by the diagonal tensor component Szz and the mixed excitation channel dominated by the off-diagonal tensor components |Sxz2 + Syz2|1/2.
Collapse
Affiliation(s)
| | - Maxim E Sasin
- Ioffe Institute, 26 Polytekhnicheskaya, St.Petersburg 194021, Russia
| | - Jesus Rubayo-Soneira
- Universidad de La Habana, Instituto Superior de Tecnologías y Ciencias Aplicadas, La Habana 10400, Cuba
| | - Andrey G Smolin
- Ioffe Institute, 26 Polytekhnicheskaya, St.Petersburg 194021, Russia
| | | |
Collapse
|
10
|
Cao S, Li H, Liu Y, Wang M, Zhang M, Zhang S, Chen J, Xu J, Knutson JR, Brand L. Dehydrogenase Binding Sites Abolish the "Dark" Fraction of NADH: Implication for Metabolic Sensing via FLIM. J Phys Chem B 2020; 124:6721-6727. [PMID: 32660250 PMCID: PMC7477841 DOI: 10.1021/acs.jpcb.0c04835] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The fluorescence of dinucleotide NADH has been exploited for decades to determine the redox state of cells and tissues in vivo and in vitro. Particularly, nanosecond (ns) fluorescence lifetime imaging microscopy (FLIM) of NADH (in free vs bound forms) has recently offered a label-free readout of mitochondrial function and allowed the different "pools" of NADH to be distinguished in living cells. In this study, the ultrafast fluorescence dynamics of NADH-dehydrogenase (MDH/LDH) complexes have been investigated by using both a femtosecond (fs) upconversion spectrophotofluorometer and a picosecond (ps) time-correlated single photon counting (TCSPC) apparatus. With these enhanced time-resolved tools, a few-picosecond decay process with a signatory spectrum was indeed found for bound NADH, and it can best be ascribed to the solvent relaxation originating in "bulk water". However, it is quite unlike our previously discovered ultrafast "dark" component (∼26 ps) that is prominent in free NADH (Chemical Physics Letters 2019, 726, 18-21). For these two critical protein-bound NADH exemplars, the decay transients lack the ultrafast quenching that creates the "dark" subpopulation of free NADH. Therefore, we infer that the apparent ratio of free to bound NADH recovered by ordinary (>50 ps) FLIM methods may be low, since the "dark" molecule subpopulation (lifetime too short for conventional FLIM), which effectively hides about a quarter of free molecules, is not present in the dehydrogenase-bound state.
Collapse
Affiliation(s)
- Simin Cao
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Haoyang Li
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Yangyi Liu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Mengyu Wang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Mengjie Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Sanjun Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Jinquan Chen
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Jianhua Xu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Jay R Knutson
- Laboratory for Advanced Microscopy and Biophotonics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Ludwig Brand
- Department of Biology, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| |
Collapse
|
11
|
Cao S, Li H, Liu Y, Zhang M, Wang M, Zhou Z, Chen J, Zhang S, Xu J, Knutson JR. Femtosecond Fluorescence Spectra of NADH in Solution: Ultrafast Solvation Dynamics. J Phys Chem B 2020; 124:771-776. [PMID: 31941277 PMCID: PMC7477843 DOI: 10.1021/acs.jpcb.9b10656] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The ultrafast solvation dynamics of reduced nicotinamide adenine dinucleotide (NADH) free in solution has been investigated, using both a femtosecond upconversion spectrophotofluorometer and a picosecond time-correlated single-photon counting (TCSPC) apparatus. The familiar time constant of solvent relaxation originating in "bulk water" was found to be ∼1.4 ps, revealing ultrafast solvent reorientation upon excitation. We also found a slower spectral relaxation process with an apparent time of 27 ps, suggesting there could either be dissociable "biological water" hydration sites on the surface of NADH or internal dielectric rearrangements of the flexible solvated molecule on that timescale. In contrast, the femtosecond fluorescence anisotropy measurement revealed that rotational diffusion happened on two different timescales (3.6 ps (local) and 141 ps (tumbling)); thus, any dielectric rearrangement scenario for the 27 ps relaxation must occur without significant chromophore oscillator rotation. The coexistence of quasi-static self quenching (QSSQ) with the slower relaxation is also discussed.
Collapse
Affiliation(s)
- Simin Cao
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Haoyang Li
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Yangyi Liu
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Mengjie Zhang
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Mengyu Wang
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Zhongneng Zhou
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Jinquan Chen
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Sanjun Zhang
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Jianhua Xu
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Jay R Knutson
- Laboratory for Advanced Microscopy and Biophotonics, National Heart, Lung and Blood Institute , National Institutes of Health , Bethesda , Maryland 20892 , United States
| |
Collapse
|