Nematic liquid crystals as sensitive layers for surface plasmon resonance sensors

Homogeneously aligned nematic liquid crystals have been tested for the sensing of volatile organic compounds using surface plasmon resonance (SPR). Oriented nematic liquid crystals are birefringent materials. A loss of birefringence of these nematic liquid crystals can be achieved by raising the temperature or by sorption of analyte. At a certain temperature, the so-called clearing point, or at a certain analyte concentration, a phase transition from the nematic to the isotropic state takes place, and the birefringence of the liquid crystal is completely lost. Within this transition, the sensor signal becomes extremely sensitive to small changes in analyteʹs concentration. Therefore the set-up can be used for threshold sensing.