MIS10-03

日本地球惑星科学連合2019年大会

プラズモン光ピンセットによる有機分子の結晶化操作と二段階溶解過程の発見“Manipulated” Organic Crystallization and Two-step Dissolution
Process Attained by Plasmonic Optical Tweezers*新家 寛正1、杉山 輝樹2,3,4、田川 美穂5、宇治原 徹5、宮本 克彦6,7、尾松 考茂6,7、野澤 純1、岡田 純
平1、宇田 聡1
*Hiromasa Niinomi1, Teruki Sugiyama2,3,4, Miho Tagawa5, Toru Ujihara5, Katsuhiko Miyamoto6,7,
Takashige Omatsu6,7, Jun Nozawa1, Junpei Okada1, Satoshi Uda1
1. 東北大学金属材料研究所、2. 国立交通大学応用化学系、3. 国立交通大学新世代効能性物質研究中心、4. 奈良先端科学技術大学院大学物質創生科学領域、5. 名古屋大学未来材料・システム研究所、6. 千葉大学分子キラリティー研究セン
ター、7. 千葉大学大学院工学研究院
1. Institute for Materials Research, Tohoku University, 2. Department of Applied Chemistry, National Chiao TungUniversity, 3. Center for Emergent Functional Matter Science, National Chiao Tung University, 4. Division of Materials
Science, Nara Institute of Science and Technology, 5. Institute of Materials and Systems for Sustainability (IMaSS),
Nagoya University, 6. Molecular Chirality Research Center (MCRC), Chiba University, 7. Graduate School ofEngineering, Chiba University

Spatiotemporal control of crystallization from a solution is often required for detailed exploration onmechanism of early stage of crystallization because the stochastic nature of nucleation process hinders us
to chase its early stage. Recently, laser trapping-induced crystallization technique has received increasing
attention as a possible candidate to realize spatiotemporally controllable crystallization.[1] In thetechnique, the crystallization is induced by trapping molecular clusters in a solution with optical tweezers,in which dielectric tiny particles are captured by electrical field gradient force generated by tightly
focusing laser light by optical lens. This technique has actually demonstrated forced nucleation of variousorganic molecules from an unsaturated mother solution at the focal spot. Although recent progress ofnanoscience including research on nucleation dynamics demands precise manipulation of nanoscopicobjects, the conventional optical tweezers, electrical field gradient force of which relies on the focusing
the laser by optical lens, has a limitation of diffraction limit on focusing the light. To overcome the limit,
the use of near-field generated by localized surface plasmon resonance, which is collective oscillation offree electrons on surfaces of metal nanoparticles when light impinges on the nanoparticle, has been
proposed. [2] Because the near-field is confined in nanoscale, the light focusing beyond the diffraction
limit can be achieved consequently, allowing us to capture the smaller particles much tightly than theconventional method. However, the plasmonic optical tweezers has never been applied to crystallization.
Here we applied plasmonic optical tweezers to crystallization of acetaminophen molecule from anaqueous solution.
Figure 1 shows schematic illustration of experimental setup. Periodic Au nanolattice the unit structure ofwhich is gammadion with the size of 500 nm was fabricated on a cover glass by electron beamlithography. An aqueous solution of acetaminophen saturated at room temperature (24oC) was dropped
on the Au nanolattice, and then solution thin layer supported by the nanolattice was formed by capillarity.
Near-infrared continuous-wave left-handed circularly polarized laser (1064 nm, 6.4×109 W/m2) was
focused to the nanolattice supporting the solution thin layer by passing through an objective lensequipped on an inverted polarized-light optical microscope. In-situ microscopic observation for thevicinity of the focal spot was also performed simultaneous with the laser irradiation.

©2019. Japan Geoscience Union. All Right Reserved.

- MIS10-03 -MIS10-03

日本地球惑星科学連合2019年大会

Figure 2 shows time-lapse micrographs of the in-situ observation in the vicinity of the focal spot. After thelaser irradiation, crystals with the size of 1000 ~ 2000 nm were precipitated 19 mm away from the focal
spot in annular pattern. The position of the annular pattern moved while following the change of in-plane
position of the focal spot via dissolution/precipitation process, indicating that position of the crystal ismanipulatable. When the plasmon excitation by laser irradiation was stopped, the crystals weredisappeared via two-step dissolution process; the crystals first transformed to dense liquid droplets, andthen the dense droplet disappeared through molecular diffusion.
Generally, large temperature gradient generates in the vicinity of the focal spot when localized surface
plasmon resonance was excited, because of the heat generation through electron-phonon scattering.
Thus, the large temperature gradient exerts thermophoretic force outward from the focal spot on
acetaminophen molecules. Since the electrical field gradient force attracts the molecules towards thefocal spot, the annular-patterned precipitation can be interpreted as the consequence of the balancing
the electrical field gradient force as attractive force and the thermophoretic force as repulsive force.
Therefore, our observation strongly suggested that plasmonic optical tweezers can precisely control
crystallization.
[1] T. Sugiyama et al., Acc. Chem. Res. 2012, 45(11), 1946-1954.
[2] T. Shoji et al., J. Phys. Chem. Lett. 2014, 5(17), 2957–2967.
キーワード：プラズモンピンセット、有機分子結晶化、二段階溶解過程
Keywords: Plasmonic Optical Tweezres, Crystallization of Organic Molecule, Two-step Dissolution Process©2019. Japan Geoscience Union. All Right Reserved.

- MIS10-03 -