This research grant supported the creation and initial development of a new kind of chemical detector; one that can detect species at part per trillion levels because it does not rely on the direct measurement of a species presence; rather, it uses an indirect measurement of the effect of the trace species on the condensation nucleation of a supersaturated vapor. Since this nucleation process is extremely sensitive to the concentrations of certain types of impurities, this nucleation-based detection can be made more sensitive than any current spectroscopic detector.