Tunable gold-coated polymer gratings for surface plasmon resonance coupling and scanning

Abstract

We propose an surface plasmon resonance (SPR) coupling device that can tune the coupling condition by changing the pitch of an Au grating. A grating with a micrometer-sized pitch was produced on a flexible thin parylene membrane, making an 8 mm × 8 mm diaphragm. An SPR can be coupled to the Au grating surface by direct laser irradiation, and the dependence of the SPR angles (within 6° to 56°) on the grating pitch (ranging from 1000 to 1500 nm) shows good agreement with the SPR theory. We demonstrate that the SPR matching condition can be tuned by changes in pitch due to strain caused by membrane expansion. The SPR angle shift reached about 0.2°, corresponding to about 0.6% strain, by 15 kPa pressure application. The SPR angle shift sensitivity to the pressure was 0.015° kPa−1. This value is almost equal to that calculated from strain measurements (0.014° kPa−1), and we conclude that the SPR angle shift was caused by the grating pitch change due to the pressure application. Theoretical consideration indicates that a refractive index change of about 0.01 RIU is possible with this device near the refractive index of water.