Design and fabrication of an alternating dielectric multi-layer device for surface plasmon resonance sensor

An alternating dielectric multi-layer device was fabricated and tested in the laboratory to show that dielectric mirrors of alternating high/low refractive index materials, based on the design of distributed Bragg reflector (DBR) for vertical cavity surface emission lasers (VCSELs), can be used in designing SPR biochemical sensors. The thickness, number of layers, and other design parameters of the device used were optimized using optical admittance loci analysis. The proof-of-concept device was fabricated with a symmetrical structure using Au/(SiO₂/TiO₂)₄/Au. Using a 632 nm-wavelength light source on a BK7 coupling prism, our laboratory tests showed that, under water, there was an 11.5° shift in resonant peak position towards the critical angle (from 74° in a conventional single-layer Au film), and a 3.25 times decrease in FWHM (the half-peak width). Our design also resulted in a wider dynamic range of up to a 1.50 refractive index unit (RIU), compared to 1.38 RIU in a conventional single-layer Au film. Using glucose solutions in ddH₂O, the calculated resolution was 1.28 × 10^-5. The calculated intensity sensitivity was 10 000 a.u./RIU, about twice the improvement over the conventional single-layer Au film.