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    Sensitive detection of a pseudo-polyrotaxane ultrathin film by SPR and QCM-D methods

    Year: 2009

    Journal: Sensors and Actuators B: Chemical, 138 (1), 24 April 2009, Pages 126-133, 20100827

    Authors: Tawa K. 1, Kuboyama N. 1 3, Ahmed S.A. 1 4, Tanaka M. 2, Nakaoki T. 3

    Last authors: Takahiko Nakaokic

    Organizations: 1 Research Institute for Cell Engineering, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan 2 Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan 3 Department of Materials Chemistry, Ryukoku University, Seta, Otsu 520-2194, Japan

    Country: Japan

    Surface plasmon resonance spectroscopy (SPR) and quartz crystal microbalance with dissipation (QCM-D) are powerful techniques to analyze structure of a thin film in sub-nanometer thickness and 10 ng cm−2 mass per area level, respectively. In this study, the pseudo-polyrotaxane in the film state was detected by both methods. The pseudo-polyrotaxane ultrathin film was composed of α-CD molecules and a self-assembled-monolayer (SAM) in which the SAM was fabricated with chains consisting of alkane thiol, a PEG chain, and an azobenzene derivative (MeAzoPEGn; PEG chain length n = 6-, 10-, and 16-mer). Though polyethylene glycol (PEG) is known to form a polyrotaxane with α-cyclodextrin (α-CD) in aqueous solution and the structure of polyrotaxane was investigated in detail, the pseudo-polyrotaxane in the film state was not studied well. SPR measurement in situ indicated resulting increases in layer thickness for a longer PEG chain in a state of equilibrium between the α-CD and the SAM. The results detected by QCM-D, showed that the film mass and rigidity increased with PEG chain length. They also provide evidence for pseudo-polyrotaxane formation. To evaluate it quantitatively, titration of the MeAzoPEGn SAMs with α-CD was measured by SPR. The increase in film thickness was found to depend on the mth order of the α-CD concentration in equilibrium state. SPR and QCM-D were found to be useful to detect the pseudo-polyrotaxane in the film state.