Solid-state optical coupling for surface plasmon resonance sensors

An optical coupling methodology using a removable and strippable polymer is reported. Poly(dimethylsiloxane) films (PDMS) are used to bond two optical components and are compared to the coupling provided by conventional refractive index matching oils and gels. The detection limit and sensitivity of the solid-state PDMS coupled optical components are investigated, using a commercially available surface plasmon resonance (SPR) instrument. Films are prepared either by an in situ curing of the PDMS pre-polymer and cast between the prism and the gold-coated glass slide of an SPR sensor or using a self standing thin film of pre-cured PDMS sandwiched between the two optical components. Both approaches lead to an efficient optical and mechanical coupling. The PDMS films may be stripped and removed very easily from the optical component surfaces after usage, due to their very low surface adhesion characteristics, reducing the messiness of the conventional optical oils and gels. The response of the PDMS-coupled SPR sensors is validated with calibration curves for both increasing sucrose and ethanol/water mass fractions. This work presents the first application of an all solid-state polymer film as an optical coupling medium in SPR and may find applications in other optical networks.