Volatile organic compounds (VOCs) are generated in the human body as a result of biological pathways such as carbohydrate metabolism, lipid metabolism and oxidative stress.  Therefore, changes in the profile of VOCs can be indicative of altered metabolic processes or liver function and can therefore be useful in diagnosing disease.  VOCs are emitted in urine, blood, skin, saliva and exhaled breath, so they can be readily monitored in diagnostic tests.  Analysis of exhaled breath is a particularly non-invasive, patient-friendly approach and the profile of VOCs from breath samples allows chemical fingerprinting for the detection and monitoring of disease.

Generally, VOC detection is by techniques such as gas chromatography (GC) and mass spectrometry (MS).  However, these can be time-consuming, costly, limited in portability and require complicated analysis.  Development of low-cost, portable devices for the sensitive detection of VOCs from breath samples is an attractive area of research due to the potential advantages in medical diagnostics.  Surface enhanced Raman scattering (SERS) is an attractive technique for this application as it is sensitive, specific, quantitative and can be used for the simultaneous detection of multiple analytes.  Additionally, portable instrumentation has been developed that allows the application of SERS at the point-of-use, with results obtainable almost instantaneously. The aim of this project is to develop a SERS-based gas sensing device for the point-of-use detection of VOCs in breath samples.  SERS detection will be compared with alternative techniques, with the aim of achieving detection limits comparable to those of mass spectrometry but with the advantages of rapid and portable analysis.  The ultimate aim will be to detect a range of VOCs related to disease so that the techniques can be applied for the diagnosis and monitoring of various health conditions.