Micro gas analyzers for environmental and medical applications

In this review, novel microsystems and microdevices to measure gaseous species for environmental analysis and medical diagnostics are described. Miniaturization of analyzers makes field measurements affordable. As well, high sensitivity and good time resolution can be achieved by miniaturization. Some such devices have already been successfully applied to real environmental analyses. Mobile monitoring is available with the use of micro gas analyzers to investigate the natural environment, air pollution and to detect nerve or explosive gases released accidentally or through terrorist activities. Miniature devices are also attractive for medical analyses. Gases produced from the human body reflect gases contained in the blood and certain metabolic conditions. Noninvasive monitoring using miniature devices is available in hospitals and in a patient's home. Many investigations have been conducted using wet and dry chemistry methods for both applications. Instruments employing wet chemistries, which comprise liquid droplets, liquid film, miniature diffusion scrubbers, and microfluidic devices have been studied. Among the instruments using dry methods, miniature samplers, portable gas chromatographs, and microfabricated gas chromatographs have all been investigated. These instruments are expected to usher in a new era of environmental monitoring and will find uses in many medical applications.