Mariko Toshimitsu, Yuriko Matsumura, Tatsuya Shoji, Noboru Kitamura, Mai Takase, Kei Murakoshi, Hiroaki Yamauchi, Syoji Ito, Hiroshi Miyasaka, Atsushi Nobuhiro, Yoshihiko Mizumoto, Hajime Ishihara, and Yasuyuki Tsuboi
Optical trapping of flexible polymer chains to a metallic nano-structured surface was explored by microscopic imaging and confocal fluorescence spectroscopy. A fluorescence-labeled poly(N-isopropylacrylamide) was targeted, being a representative thermo-responsive polymer. Upon resonant plasmonic excitation, it was clearly observed that polymers were assembled into the excitation area to form molecular assemblies. Simultaneously, fluorescence from the area was obviously intensified, indicating an increase in the number of polymer chains at the area. The excitation threshold of light intensity that was required for obvious trapping was 1 kW/cm2, which was much lower by a factor of 104 than that for conventional trapping using a focused laser beam. The morphology of the assemblies was sensitive to excitation intensity. We precisely evaluated temperature rise (
T) around the metallic nanostructure upon plasmonic excitation: T ~ 10 K at 1 kW/cm2 excitation. This temperature rise was an origin of a repulsive force that blocked stable trapping. Based on experimental observations and theoretical calculations, we quantitatively evaluated the plasmon-enhanced trapping force and the thermal repulsive force (Soret effect). The overall mechanisms that were involved in such plasmon-enhanced optical trapping are discussed in detail. The smooth catch-and-release trapping (manipulation) of polymer chains was successfully demonstrated.
DOI
Optical trapping of flexible polymer chains to a metallic nano-structured surface was explored by microscopic imaging and confocal fluorescence spectroscopy. A fluorescence-labeled poly(N-isopropylacrylamide) was targeted, being a representative thermo-responsive polymer. Upon resonant plasmonic excitation, it was clearly observed that polymers were assembled into the excitation area to form molecular assemblies. Simultaneously, fluorescence from the area was obviously intensified, indicating an increase in the number of polymer chains at the area. The excitation threshold of light intensity that was required for obvious trapping was 1 kW/cm2, which was much lower by a factor of 104 than that for conventional trapping using a focused laser beam. The morphology of the assemblies was sensitive to excitation intensity. We precisely evaluated temperature rise (
DOI
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