Efficient Immobilization of Polymer Gels on Gold Substrate and Evaluation of Their Thermal Responses by Laser-Induced Surface Plasmon Resonance

The resonance excitation of a surface plasmon (SP) or surface plasmon resonance (SPR) occurs at a characteristic angle of incidence, which depends on the thicknesses and as on the dielectric permittivities of the layers and of the adjacent medium. Therefore, SPR techniques have been extensively investigated in the fields of bio-assay and gas sensor. However, to our knowledge, there are no experimental data of SPR in stimuli-response polymers. In this study, polymer gels were immobilized on gold substrates and their thermal responses were investigated by SPR. The gold surface was modified with silane-couplers having a mercptan group and a double bond. Polymerization on modified gold substrate was carried out to obtain polymer gels immobilized on the gold. SPR angle of poly (N-isoplopylacrylamide) (PNIPAAm) gel on gold substrate increases to high incident angle with increasing temperature up to 40r but decreases to low incident angel at 60°C. SPR angle of poly (acrylamid) (PAAm) gel and pristine gold substrate decrease to lower incident angles with increasing temperature. Thus, these SPR angle shifts were ascribed to the differences in the thermal responses of the polymers. Polymer gels are firmly fixed on a gold substrate and did not peel off after thermal tests. We succeeded in efficient immobilization of polymer gels on modified gold surfaces. Thermal-responses of polymer gels could be evaluated by SPR.