Design Features of Surface Plasmon Resonance Sensors

Abstract

The two sensing modes under consideration, the angular (AIM) and spectral (WIM) modes, exhibit advantages and disadvantages in terms of technical complexity, data processing and operating conditions. Schematics of the AIM and WIM optical set-up are shown in Fig. 3.1a, b, respectively. Each setup comprises a flat dove type prism chip. The design route allows the construction of compact instruments and avoids implementation of a bulky optical prism. The optical function of SPR prism chip is similar to a waveguide. In the AIM, incident radiation is a spectrally narrow band, while the angle range is wide and the resonance angle is recorded. In the WIM, the incident radiation is spectrally broadband, the incident angle range is narrow, comprising a collimated light beam, and a spectrometer tracks the resonance wavelength. A third-less popular-hybrid sensor configuration is the Intensity Mode (IM), as shown in Fig. 3.1c, where a collimated beam at a fixed (resonance) angle and wavelength is employed. The temperature coefficient of the refractive index of water at ambient T, with -1.2 × 10-4 RIU/˚C, is quite high and exceeds those of the optical components, typically used in the optics design. Hence, it should be recalled that SPR sensors are particularly sensitive to temperature fluctuations. They are also sensitive to mechanical vibrations or thermal distortions in the optical path, down to the micrometer or even sub-micrometer levels. A rigid mechanical design is therefore beneficial. Surface conditions, preparation and functionalization, as well as long term temporal stability and signal drift effects are further important issues, since recordings may last for several hours.