Liquid Sensor Based On Optical Surface Plasmon Resonance in a Dielectric Waveguide

In this work, we have demonstrated an optical surface Plasmon resonance (SPR) sensor head that is based on an inverted rib dielectric waveguide, in which the resonance wavelength of the surface plasmon excited at the gold metal-dielectric interface changes in relation to changes of the environment at the top metal surface. The inverted-rib waveguide of the SPR sensor head is made of a layer of SU-8 polymer with a refractive index of 1.5 while the lower cladding layer consists of silicon oxynitride (SiO Ny) with a refractive index of 1.526. The top surface is coated with a 50 nm thick layer of gold. The SPR sensor head was designed to allow monitoring of analyte media with a refractive index ranging from 1.44 to the 1.502. Using a set of reference liquids representing the analyte medium, the sensitivity of the SPR sensor was measured using a broadband light source and a optical spectrum analyzer. It was found that with a liquid of 1.442 refractive index in contact with the gold metal, a sharp resonance dip in the transmission spectrum occurred at 1525 nm and its position shifted to 1537 nm when a liquid of 1.502 was used. From these measurements, the sensitivity of the sensor devices wasdetermined to be S = 232 nm.RIU-1. We demonstrate that this device can potentially be totally integrated with a wavelength tunable light source, a photodetection unit as well as a liquid delivery system via microfluidic channels making it an extremely compact unit.