*4.3. OWLS Immunosensor Measurements*

OWLS sensoric determinations were carried out in a flow-through cell of the OWLS 210 instrument. The optical grating of the sensor surface is illuminated with a polarised He-Ne laser light (632.8 nm), and the sensor chip is rotated along its axis in a narrow angle range (±7 ◦ ). The laser beam is diffracted on the grating, and enters the waveguide at the characteristic incoupling angles, where it propagates by total internal reflection, and is detected by photodiodes at the ends of the waveguide layer. Incoupling of the incident laser

beam occurs at two well-defined angles of incidence: one for transverse electric (TE) and one for transverse magnetic (TM) mode. Rotating the cuvette with ±7 degrees, effective refractive indices (NTE and NTM) are monitored, and four characteristic photocurrent peaks (TE and TM peaks on both, positive and negative sides) can be detected at the incoupling angles αTE and αTM. Apparent incoupling angles can be measured with 10−<sup>4</sup> degree accuracy, and signal resolution relative to the effective refraction index is ∆N~10−<sup>6</sup> . The mass of the deposited material absorbed on the waveguide surface from the continuous-flow medium can be calculated from the effective refractive indices (NTE and NTM), expressed as thickness of the protein layer deposited (nm) or surface coverage (ng cm−<sup>2</sup> ). All determinations were carried out at room temperature in a flow-injection analyser system at a flow rate of 200 µl/min and with injection volumes of 200 µL.
