田原分子分光研究室 Molecular Spectroscopy Laboratory



Development of novel single-molecule methods and application to elucidate complex behavior of biomolecular systems

Kunihiko Ishii

The single-molecule spectroscopy group is engaged in the development of new methods of single-molecule fluorescence spectroscopy and related photon data analysis. By utilizing the developed methods, we investigate the complex behavior of biomolecular systems, such as proteins, nucleic acids, and lipid membranes. Through the integrated approach of laser spectroscopy, biophysical chemistry, and statistical data analysis, we pursue creating a new field of molecular science.

Research outline

Biopolymers (e.g., proteins and nucleic acids) and biomolecular assemblies (e.g., lipid membranes) are important classes of molecular systems which constitute life. Since they consist of a large number of atoms and have a high structural degree of freedom, such complex biomolecular systems flexibly change their structures under room temperature. Behind this flexibility, there exists a structural hierarchy, and correspondingly, their dynamics reveals a broad range of characteristic time scales. This hierarchy leads to structural heterogeneity and complex dynamics of the biomolecular systems, which, in turn, plays crucial roles in the biological functions.
To examine the structural heterogeneity and spontaneous dynamics of complex biomolecular systems, an attractive and powerful way is to measure single molecules one by one, instead of observing the average response of many molecules. However, because in general, the spectroscopic signal emitted from a single molecule is extremely faint, it is not a simple task to know much about the molecular property through the observed single-molecule data. We are developing novel experimental and analytical tools having high information content based on time-resolved single-molecule fluorescence spectroscopy and photon correlation analysis. We aim at elucidating the complex behavior of biomolecular systems through making use of these original methods.


Development of a new correlation spectroscopy method for observing fluorescence lifetime fluctuations

Solvation and local motion of protein side chains studied by femto- and picosecond time-resolved fluorescence spectroscopy (collaboration)

Study of protein folding with a microsecond time resolution using two-dimensional fluorescence lifetime correlation spectroscopy


Kunihiko Ishii (group leader)

Miyuki Sakaguchi

Bidyut Sarkar

Kazuto Hasegawa

Selected publications

  1. T. Otosu; K. Ishii; H. Oikawa; M. Arai; S. Takahashi; T. Tahara
    Highly heterogeneous nature of the native and unfolded states of the B domain of protein A revealed by two-dimensional fluorescence lifetime correlation spectroscopy
    J. Phys. Chem. B 121, 5463-5473 (2017).
  2. T. Otosu; K. Ishii; T. Tahara
    Microsecond protein dynamics observed at the single molecule level
    Nat. Commun. 6, 7685 (2015).
  3. K. Ishii; T. Otosu; T. Tahara
    Lifetime-weighted FCS and 2D FLCS: Advanced application of time-tagged TCSPC
    In: P. Kapusta, M. Wahl, R. Erdmann (eds.), Advanced Photon Counting. Springer Series on Fluorescence (Methods and Applications), 15, Springer, Cham, 111-128 (2014).
  4. K. Ishii; T. Tahara
    Two-dimensional fluorescence lifetime correlation spectroscopy. 2. Application
    J. Phys. Chem. B 117, 11423-11432 (2013).
  5. K. Ishii; T. Tahara
    Two-dimensional fluorescence lifetime correlation spectroscopy. 1. Principle
    J. Phys. Chem. B 117, 11414-11422 (2013).