The Mid-infrared (MID-IR) wavelength range has been of great interest in regard to sensing and spectroscopic applications. This wavelength range carries an absorption band for various gases, bio-materials as well as lots of molecules. It also overlaps with the atmosphere transparent windows of 3-5 μm and 8-13 μm, which is an important figure-of merit to fabricate an entire sensing system. However, current sensing systems in MID-IR range are typically bulky and expensive. At present, they cannot be portable, whereas there would be a lot of demands of sensors in IOT era. Therefore, what is needed is a technology platform for producing highly compact sensor systems. Therefore, we aim to develop flexible gas sensors using Mid-IR photonic platform based on Germanium (Ge)-on-insulator.