Development of highly sensitive sensing techniques is needed for the analysis of biological functions of biomaterials such as DNAs and proteins. We have been developing biosensors by using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). MIR-IRAS provides us with valuable information about chemical states of biomolecules, biomaterials and cells. In this report, we describe some experimental techniques that would be helpful in performing MIR-IRAS measurements.