1. Current Research and Principal Research Interests

Raman Microspectroscopy combined with Optical Tweezers

Thermo-responsive polymers have attracted much attention in the field of organic functional material science over the past 40 years since the first discovery of the phenomenon; thermo-responsive phase separation in solution. Poly-(N-isopropylacrylamide) (PNIPAM) is a representative water-soluble thermo-responsive polymer. PNIPAM can homogeneously dissolve in water at room temperature, taking a hydrated random-coiled structure. Upon raising temperature above a lower critical solution temperature (LCST = 32 °C), the polymer exhibits coil-to-globule structural transition accompanied by dehydration of the polymer chains. The dehydrated globules aggregate with each other due to hydrophobic interactions, and consequently forming polymer-rich domains in solution (phase separation). Quantitative analysis of a single polymer-rich domain is a challenging task for deeper understanding of the phenomena. Raman microspectroscopy would be a powerful candidate for evaluating it. In this case, it is necessary to selectively obtain precise Raman spectra only of a polymer-rich domain that is micron-sized and continuously fluctuated by the Brownian motion in solution. Confocal Raman microspectroscopy combined with optical trapping technique is a powerful tool for such purpose.

A recent work found that a confocal Raman microspectroscope combined with optical tweezers is a promising technique to estimate polymer concentration in polymer-rich domain in phase-separated-aqueous polymer solution. Optical tweezers can selectively trap the polymer-rich domain at the focal point in non-contact and non-intrusive modes. Such situation allows us to determine polymer concentration in the domain, which has been unclear due to a lack of appropriate analytical technique. It is applicable for a variety of other thermo-responsive polymers.

from Anal. Chim. Acta (2015)

2. Selected Publications

  1. A method for an approximate determination of a polymer-rich-domain concentration in phase-separated poly(N-isopropylacrylamide) aqueous solution by means of confocal Raman microspectroscopy combined with optical tweezers
    • Tatsuya Shoji, Riku Nohara, Noboru Kitamura and Yasuyuki Tsuboi
    • Anal. Chim. Acta, Vol. 854 (2015), pp. 118-121.
  2. Plasmonic Optical Tweezers toward Molecular Manipulation: Tailoring Plasmonic Nanostructure, Light Source, and Resonant Trapping
    • Tatsuya Shoji, Yasuyuki Tsuboi
    • J. Phys. Chem. Lett., Vol. 5 (2014), pp. 2957-2967.
  3. Permanent Fixing or Reversible Trapping and Release of DNA Micropatterns on a Gold Nanostructure Using Continuous-Wave or Femtosecond-Pulsed Near-Infrared Laser Light
    • Tatsuya Shoji, Junki Saito, Noboru Kitamura, Fumika Nagasawa, Kei Murakoshi, and Yasuyuki Tsuboi
    • J. Am. Chem. Soc., Vol. 135 (2013), pp. 6643-6648.
  4. Resonant Excitation Effect on Optical Trapping of Myoglobin: The Important Role of a Heme Cofactor
    • Tatsuya Shoji Noboru Kitamura, and Yasuyuki Tsuboi
    • J. Phys. Chem. C, Vol. 117 (2013), pp. 10691-10697
  5. Reversible Photoinduced-Formation and Manipulation of a Two-dimensional Closely Packed Assembly of Polystyrene Nanospheres on a Metallic Nanostructure
    • Tatsuya Shoji Noboru Kitamura, Fumika Nagasawa, Kei Murakoshi, Hajime Ishihara, and Yasuyuki Tsuboi
    • J. Phys. Chem. C, Vol. 117 (2013), pp. 2500-2506.
  6. Plasmon-Based Optical Trapping of Polymer Nano-Spheres as Explored by Confocal Fluorescence Microspectroscopy: A Possible Mechanism of a Resonant Excitation Effect
    • Shoji, Tatsuya; Mizumoto, Yoshihiko; Ishihara, Hajime; Kitamura, Noboru; Takase, Mai; Murakoshi, Kei; Tsuboi, Yasuyuki
    • Jpn. J. Appl. Phys., Vol. 51 (2012), 092001.
  7. Plasmon-Based Optical Trapping of Polymer Nano-Spheres as Explored by Confocal Fluorescence Microspectroscopy: A Possible Mechanism of a Resonant Excitation Effect
    • Shoji, Tatsuya; Mizumoto, Yoshihiko; Ishihara, Hajime; Kitamura, Noboru; Takase, Mai; Murakoshi, Kei; Tsuboi, Yasuyuki
    • Jpn. J. Appl. Phys., Vol. 51 (2012), 092001.
  8. Metallic-Nanostructure-Enhanced Optical Trapping of Flexible Polymer Chains in Aqueous Solution as Revealed by Confocal Fluorescence Microspectroscopy
    • Toshimitsu, Mariko; Matsumura, Yuriko; Shoji, Tatsuya; Kitamura, Noboru; Takase, Mai; Murakoshi, Kei; Yamauchi, Hiroaki; Ito, Syoji; Miyasaka, Hiroshi; Nobuhiro, Atsushi; Mizumoto, Yoshihiko; Ishihara, Hajime; Tsuboi, Yasuyuki
    • J. Phys. Chem. C, Vol. 116 (2012), pp. 14610-14618.
  9. Nano Porous Films Processing of Polymer Films Based on Localized Surface Plasmon Resonance of Au Nanoparticles
    • Muraoka, Keita; Yamada, Kazushi; Shoji, Tatsuya; Sugimura, Hiroyuki; Kitamura, Noboru; Tsuboi, Yasuyuki
    • J. Laser Micro. Nanoen., Vol. 7 (2012), pp. 260-263.
  10. Optical trapping of amino acids in aqueous solutions
    • Tsuboi, Yasuyuki; Shoji, Tatsuya; Kitamura, Noboru
    • J. Phys. Chem. C, Vol. 114 (2010), pp. 5589-5593.