© 2014 American Chemical Society. A new optical gas sensor platform based on highly luminescent ZnO-polymer nanohybrids is demonstrated. The nanohybrids consist of ZnO nanoparticles, typically 125 (±25) nm in size, dispersed in an inert cross-linked polydimethylsiloxane (PDMS) matrix. Upon exposure to ethanol-enriched air at room temperature, the nanocomposites exhibit a clear increase in their photoluminescence (PL) emission, which shows a nearly Langmuir dependence on the alcohol vapor pressure. The response time is on the order of 50 s, particularly at low ethanol concentrations. The limit of ethanol vapor detection (LOD) is as low as 0.4 Torr, while the sensor remains unaffected by the presence of water vapor, demonstrating the potential of the ZnO-PDMS system as an optical gas sensing device. The interaction of the ZnO nanoparticles with molecular oxygen plays an essential role on the overall performance of the sensor, as shown in comparative experiments performed in the presence and absence of atmospheric air. Notably, O2 was found to be quite effective in accelerating the sensor recovery process compared to N2 or vacuum.