Since CO2 has gotten a lot of attention in the past (climate change for example), there is a lot of interest in reducing the size and cost of CO2 sensors and subsequently allow a mass production of these sensors. As semiconductor technology allows for a realization of these requirements, a project was initiated by Infineon. A team at the JKU-Linz, led by Prof. Jakoby, made the theoretical design of this sensor. The working principle of these sensors is the absorbance of the evanescent field of a sub-wavelength waveguide, as I will explain in the talk. Part of my thesis was the design of a test bench used for an optical and electrical characterization of the waveguides and measurements of the absorbance of CO2 and Chloroform with the waveguide sensors. I will also talk about advantages and disadvantages of the waveguiding technology and give a future outlook on the project.