Recent developments in liquid phase mid-infrared sensor technology

The potential of mid-infrared optical sensing technology for liquid phase applications is tightly related to the implementation of appropriate chemical modifications of the sensing surface. Besides recognition and enrichment of analyte molecules, suppression of interfering water absorptions is of substantial interest. Utilizing the principle of evanescent wave spectroscopy for the signal generation is the basis for the realization of powerful spectroscopic sensing systems, which provide access to molecule specific vibrations of organic analytes. With the availability of mid-infrared transparent fiberoptic materials, access to the mid-infrared spectral region from 2-20 mum is gained enabling remote qualitative and quantitative analysis. Besides polymeric molecular recognition and enrichment layers, sol-gel films are among the most promising surface modification. This highly reproducible process allows detailed control on the surface properties of the sol-gel layer formed at the waveguide surface. Due to the inertness and robustness of sol-gel coatings they can be considered among the most promising surface modification materials for optical sensors applied in the biomedical and biological field.