The response of semiconductor-based adsorption modified photosensitive sensor is based on the dye-enhanced photoconductivity of a CdS semiconducting film. The change in this photoconductivity is brought about when organic molecules are sorbed onto the dye-coated surface. The response is related to the overlap in the infrared spectrum of the dye with that of the analyte.

This research was carried out to study the response of the sensor to a typical hydrocarbon, toluene. The sensor was tested for its response to concentrations of toluene ranging from 2.6 ppm to 200 PPM in nitrogen. The sensor was tested under non-flow conditions and in the absence of oxygen and water vapor. Under these conditions, the Rhodamine B dye coated sensor was found to respond to changes in toluene concentration. The photoresistance of the sensor decreased as the concentration of toluene increased. The sensor showed high changes in photoresistance for lower toluene concentrations. Also, the rate of change of photoresistance was higher for higher concentrations of toluene. The sensor itself was very stable to long exposures to light but showed poor desorption characteristics. The sensor had to be flushed with nitrogen for extended periods to ensure complete desorption of adsorbed toluene.

This study forms the basis of future testing to be performed under more practical conditions, in the presence of water vapor and oxygen.