PDMS prism-glass optical coupling for surface plasmon resonance sensors based on MEMS technology

A miniaturized surface plasmon resonance （SPR） chip has been developed for biomedical and chemical analysis with low cost and high performance. The techniques of bulk silicon micromachining and polymer replication were used to fabricate the Kretschmann SPR sensor composed of a Polydimethylsiloxane （PDMS） prism, a coupling glass and microchannels. The plasmon properties of thin metal films were investigated theoretically based on Fresnel analysis, with optical boundary conditions pertaining to the surface plasmon resonance at the gold/water and gold/air interfaces. The theoretical results show that difference in the refractive index （RI） between the PDMS prism and the coupling glass layer affect the precision of the SPR angle and the SPR curve. Meanwhile, the period of the interference fringe attaching on the SPR curve increases with an increase in wavelength and a decrease in the refractive index of the coupling glass layer. The gold thickness of 50 nm is required while employing a fixed incident wavelength of 650 nm, to achieve optimum SPR excitation conditions and the sensor sensitivity. The characteristics of this SPR sensor were evaluated in the angular interrogation mode of employing the incident wavelength of 650 nm in air and water media, respectively. The obtained SPR angles were approximately consistent with the theoretical ones.