Surface plasmon resonance sensor based on a new opto-mechanical scanning mechanism

Abstract

Surface plasmon resonance (SPR) is employed as one of the key phenomena in biological, chemical and gas sensors. In this paper, we report development of a Kretschmann configuration based SPR sensing instrument by adopting a unique opto-mechanical scanning mechanism. The new scanning mechanism ensures portable, very low-cost and sensitive SPR sensor. In contrary to the traditional scanning mechanism, we utilized a rotating mirror for changing angle of incidence, and a quadrant photodiode (QPD) for recording reflected intensity. In order to achieve constant spot measurement on the sensing area (gold surface) for a fixed referencing, the prism-sensor assembly is translated vertically in a highly controlled manner governed by a feedback mechanism. In the feedback mechanism, the deflection of reflected beam is quantified by the QPD, and the prism-sensor assembly is translated vertically so as to regain the original set point. The SPR spectra of different materials deposited onto the gold surface using different techniques were collected and studied. Using the developed SPR instrument with pure gold sensing surface, the lowest detectable concentration of the sucrose in aqueous medium was found to be 100 femto-molar. The sensitivity of the instrument was estimated using the different concentration of aqueous solutions of sucrose with known refractive indices, and it was found to be around 52.6°/RIU. These studies indicate a high resolution and good sensitivity of the instrument.