Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 116, Issue 27, Pages 14610-14618Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp305247a
Keywords
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Funding
- Ministry of Education, Culture, Sports, Science, and Technology of Japan [19049004, 20550002]
- Ministry of Education, Culture, Sports, Science, and Technology of Japan in Global COE [B01]
- Grants-in-Aid for Scientific Research [20550002, 23681023, 23310079, 23340086, 23245004, 23654105] Funding Source: KAKEN
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Optical trapping of flexible polymer chains to a metallic nanostructured 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/cm(2), which was much lower by a factor of 10(4) 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 (Delta T) around the metallic nanostructure upon plasmonic excitation: Delta T approximate to 10 K at 1 kW/cm(2) excitation. This temperature rise was an origin of a repulsive force that blocked stable trapping. On the basis of 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 hi. such plasmon-enhanced optical trapping are discussed in detail. The smooth catch-and-release trapping (manipulation) of polymer chains was successfully demonstrated.
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