Plasmonic-enhanced conjugated polymer fluorescence chemosensor for trace nitroaromatic vapor

We report the combined use of low-density, ultra-thin oxide capping layers and plasmonic silver gratings to improve the utility of ultra-thin fluorescent conjugated polymer films for long-term, portable chem/bio sensing applications. Silver gratings produced by a low-cost micro-contact printing method enhance emission of poly-[2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) as much as 12-fold with respect to films on flat silver primarily through surface plasmon-coupled emission. Addition of a low-density, 5 nm SiO2 capping layer improved MEH-PPV photostability with respect to uncapped films under both continuous illumination as well as long-term storage in dark, ambient air, while retaining a rapid quenching response to nitroaromatic vapors. Capped, plasmonic-enhanced MEH-PPV film demonstrated 7-fold faster quenching to 2,4-dinitrotoluene vapor than capped films on SiO2-coated silicon, attributed to competition between surface plasmon-coupled emission and non-radiative energy transfer pathways. Additionally, the devices recover fluorescence spontaneously on removal from the nitroaromatic vapor source, suggesting they could be used for long-term, real-time measurements of nitroaromatic vapors. (C) 2014 Elsevier B.V. All rights reserved.