"The proposed cross-disciplinary project takes ultra-sensitive optical cavity ring-down spectroscopy (CRDS) beyond the state of the art by allowing practical CRDS instruments in the mid-IR spectral range where many analytically interesting gas molecules have strongest absorption. Such a step change in CRDS technology is enabled by the recent advances of the quantum cascade lasers. The cutting edge sensor technology will be used to address two topical and high impact cross-disciplinary measurement challenges. The first challenge is in the field of medical exhaled breath analytics and the second one in the measurement of carbon isotope 14-C/12-C ratio.Every year over 100 million people undergo surgery, mostly performed under general anaesthesia.The majority of operations are performed using inhaled anaesthetic agents. However, more and more patients are anaesthetised using intravenously administered drugs, such as propofol, because there is growing evidence that intravenously administered drugs have several advantages over inhaled ones: shorter recovery times and less frequent adverse side effects. Compatibility with other drugs is also better, which is crucial for balanced anaesthesia. The increasing clinical use of intravenous anaesthetics is accompanied by the alarming fact that no viable instruments exist for monitoring their blood plasma concentration.The second application, analysis of carbon 14-C/12-C isotope ratio from CO2 samples, responds to the emerging need to monitor the fossil to modern carbon ratio and to detect leakages in Carbon Capture and Storage (CCS) systems. The EU Emissions Trading Scheme, together with the proposed CCS Directive, are expected to keep the EU on track to meet its target to cut greenhouse gas emissions in Europe by 20% by 2020 compared to 1990 levels. CCS is emerging technology concept and currently there is no established state of the art, particularly with regards to monitoring of CO2 leakages in the storage strata."