Design Of Breath Acetone Analyzer Based On Cavity Ring-down Spectroscopy

As developing of modern medical technology and interdisciplinarity, early diagnosis, a leading research area in medicine, has been making breakthroughs and innovations, especially, the breath Biomarker technology for diagnosis of critical illness. Numerous medical studies showed that particular chemical composition in breath implies one’s metabolic status and health condition. These metabolic product will be changed correspondingly when visceral organ or tissue is damaged and its function is altered. These by-products proliferating to alveolar space through pulmonary blood-air barrier, changing exhaled gas’s components, and evaluating some particular volatile organic compounds(VOCs), thus can be selected as biomarkers of a number of diseaseGas Chromatograph-Mass Spectroscopy(GC-MS), whose detect limit is as low as part per billion (ppb) or par per trillion(ppt), is a traditional method in breath analysis. This method, however, is time consuming, huge bulky and considerable expensive, so that not be able to applied to clinical but only conduct laboratorial research, let alone miniaturizing and entering communities and families. As a high precision and sensitive absorb spectroscopic technology, Cavity Ringdown Spectroscopy(CRDS) has lots of advantages such as result immune to fluctuation of laser source, long effective absorption optical path, high precision and sensitivity. It is highly potential to be first choice of breath analysis in the future;According to the specification of acetone’s special spectroscopic property, this dissertation focused on acetone, a breath biomarker of diabetes mellitus, and chose an appropriate laser as light source. After analyzed reasons of every module the author designed and constructed platform for acetone analysis based on CRDS and verified principle of this technology. It performs at a uncertainty as low as0.4%, which shows great reproducibility. Then spectroscopic absorption of lab’s air,5.95±0.25×10-4, and healthy human breath, was determined by this system, and its stability is as low as1.4%. At last, concentration of human’s breath acetone was analyzed as a pilot study for non-invasive measurement of blood glucose.This dissertation is consist of five chapters:First chapter has detailed medical background of breath analysis, research significance, and development of domestic and aboardSecond chapter has described discipline of CRDS and constructing of breath analytical system, then analyzed every module of this system including light source, cavity, detector and data acquisition.Measuring Ringdown signal, calculation reflection of high-R mirrors has been showed in chapter3. The reflectivity of High-R mirror is calculated as99.58%. Stability of vacuum cavity and measuring healthy human breath is0.4%and1.4%, perspectively. Absorption of lab’s air,5.95±0.25×10-4, and healthy human breath, was determined by this system. Health human breath acetone is also analyzed.Primary errors and artifacts influencing accuracy of this system has been discussed in chapter4. Three types, optical errors, detecting circuit noise and signal artifacts, are the main source of system’s noise. Some aspects which will effect system’s accuracy has been discussed, including laser spot, interference, diffraction, scattering, noise from photomultiplier tube(PMT), artifacts of spectroscopy and biology.At last, system of breath analysis based on CRDS has been summarized and describe the future research scheme.