4.2.   SPR Setup

The SPR device used for the measurements of this work is a single sensor device, which is based on the resonance of surface plasmons as detection principle. The setup, which is shown in figure 11 and which was assembled by Dr. Birgit Kieser [171], was initially suggested by Kretschmann in 1968 [172]:

At constant angle, parallel-polarized white light is focused through a glass prism onto a silver film on condition of total reflection. The surface plasmons are excited at the back surface of the silver layer, which is evaporated onto the glass prism. The reflected light is coupled into a multimode fiber and detected by a diode array spectrometer. A sensitive polymer layer is coated onto the top of the silver film. The resonance wavelength of the surface plasmons is influenced mainly by the refractive index n and partly by the thickness d of the sensitive layer (for all sensitive layers used in this work practically only changes of the refractive index n play a role [173]). Due to a high temperature dependency of the refractive index, the temperature was kept constant by a thermo-regulator. More details of the setup can be found in literature [174].

figure 11:  Schematic of the RIfS array setup. The yellow bubbles show the effects when analyte sorbs into the polymer layer (magenta).