| dc.description.abstract | This thesis discusses the preliminary development of a microfluidic system for low
concentration vapour analysis incorporating a novel analyte preconcentration method to
extend vapour detection limits. The topicality of this subject is evidenced by the urgent requirement to detect vapours released by explosives or their manufacturing byproducts,
allied to recent reports of gas phase detection of pathogen-related chemical markers.
Commercially available, non-microfluidic, sensitive, delayed response, broadly specific, gasphase
analysis methods have been developed recently. However microfluidic analysis
offers the prospect of both the improved specificity of liquid phase analytical methods and
increased sensitivity with fast response times. The necessary conditions to achieve a viable
microfluidic vapour analysis system are discussed from collection, sampling, assay and
measurement perspectives.
Efficient, rapid, vapour collection into a liquid phase is predicated by large surface area to
volume ratio phase-interfaces, as occur within microfluidic devices. Accordingly, research
has focussed on stable, segmented gas and liquid microflows. The literature has
concentrated on fixed structures and precise flow rate control to produce such segmented
flow. In contrast, we have investigated pressure driven flow and small active valves in
combination with precision patterned passive valves to provide deterministic control over
flow and thus define gas and liquid segment sizes. This has allowed introduction of larger,
precise gas volumes and hence gas/liquid ratios while still maintaining more stable flow
patterns than those previously reported in the literature.
Ethanol was employed as a completely soluble, volatile, ‘model’ analyte to assess collection
efficiency. Research into detection focussed on a number of optical methods utilising either
‘wet’ or enzymatic chemistries. The Phase-to-Phase Extraction via a Chemical Reaction to
give Lower Limits of Chemical Detection hypothesis (for the purpose of brevity this is
shortened to ‘Chemical Amplification’ within this dissertation) was proposed. Thorough
testing of the hypothesis using an enzyme catalysed reaction scheme has demonstrated its
validity, and potential value if applied to ‘real world’ systems, particularly those for detecting
low solubility analytes such as the explosive 2,4,6-trinitrotoluene (TNT) or its byproduct 2,4-
dinitrotoluene (2,4-DNT). | en |
