Many gases that we want to detect or monitor in our environment have bands of absorption lines in the mid-infrared (midIR). These absorption lines form a "fingerprint" for a particular molecule, hence midIR spectroscopic sensing systems allow detecting the presence (and concentration) of specific molecules. These spectroscopic gas sensing systems find applications in environmental monitoring (e.g. car exhaust monitoring, air quality assessment), but also in biomedical applications. It is known that the concentration of certain compounds (e.g. NO and CO) in the exhaled breath of a patient can indicate for example diabetes or renal diseases. However, the full potential of midIR spectroscopy has not yet been deployed due to the lack of high-sensitivity, affordable and portable instrumentation. In this project we want to make key advances in this field by realizing widely tunable, compact and low-cost quantum cascade lasers emitting in the mid-infrared wavelength range. The wavelength setting and tuning mechanism is based on integrated wavelength selective feedback of light in the semiconductor laser cavity, which is realized by a thermally tuned silicon-based photonic integrated circuit. This approach differentiates itself from the state-of-the-art systems, which require movable external diffraction grating mirrors to provide feedback, and can lead to the ubiquitous deployment of such laser sources in handheld devices that monitor our everyday environment or our health.