Surface plasmon resonance based refractive index sensor for liquids

Abstract

A surface plasmon resonance (SPR) refractive index sensor for liquids was fabricated and characterized. A thin silver (Ag) film (545A) was deposited on a prism face and surface plasmon modes were excited along the interfaces of Ag and air, Ag and water and Ag and sugar solutions by prism-coupling using a He-Ne laser. The experimental SPR reflectance curves shifted continuously with increase in sugar concentration. Theoretical fitting of the SPR dip angles yielded the dielectric constant of Ag and refractive indices of water and sugar solutions. A maximum sensitivity of 1.4×10 - 4 R.I.U. (refractive index units) was achieved with SPR dip angle as variable parameter. With SPR reflectance as variable parameter at a fixed angle, the maximum sensitivity was 3.9×10 - 5 R.I.U. in a selected narrow range of refractive index.