Early stage discovery of lung cancer can significantly improve patient prognosis. Unfortunately, the impact of a well-known technique such as computed tomography screening on mortality rates is uncertain. It has been postulated that tumor growth may lead to peroxidation of cell membranes and is responsible for the observed emission of volatile organic compounds (VOC’s) such as acetone and formaldehyde. This observation has stimulated significant recent effort in the measurement of these compounds in exhaled breath. While promising approaches have been developed for analyzing average VOC concentrations in exhaled breath, an unrecognized drawback to current efforts is the presumption that gas partitioning between the blood and gas phases occurs so rapidly that the time averaged concentration of collected VOCs is representative of their saturation concentration in the lungs. In fact, when one considers the mass transport resistances encountered, VOC lung concentration is likely to be time-dependent and any sensing approach must have sufficient time resolution to capture the dynamic evolution of this concentration during a typical breath exhalation period of not more than 40 seconds in a high humidity environment.

In this presentation, we describe development of an optical exhaled gas sensing approach utilizing a nanostructured polymeric membrane that meets these requirements and demonstrates the dynamic evolution of exhaled breath biomarker concentration. We show that the activity of a solid acid catalyst toward the heterogeneous condensation reactions of immobilized resorcinol reagent with gas-phase acetone and formaldehyde can be preserved even at 100% ambient relative humidity through the incorporation of organic acids such as vanillic or tiglic. The reaction produces a colored flavan and poly-condensation products that permits highly selective and sensitive correlation to acetone and formaldehyde concentrations in exhaled breath. Such behavior relies on the complex heterophase morphology of the membrane as will be described.