Amplified response and enhanced selectivity of metal-PANI fiber composite based vapor sensors

Nanocomposites of polyaniline (PANI) nanofibers and metal nanoparticles were fabricated using a single-step photo-assisted technique and tested as sensors. Nanofiber composites containing Ag- and Pt-nanoparticles were exposed to toluene and triethylamine and their response was compared to that of bare nanofibers and bulk PANI produced with the same technique. The larger surface areas of the nanofiber-based sensors resulted in shorter response times and in larger changes in conductivity than for bulk PANI sensors for all analytes. Nanofiber sensors with and without Ag or Pt particles had a comparable response when exposed to toluene, an analyte that induces swelling of the composites, but does not alter doping or react strongly with nanoparticles of noble metals. The composites reacted quite differently to triethylamine. The response time of Ag-containing composites was about 3 times faster than that of the nanofibers alone and about 1.5 times faster than that of PANI–Pt nanocomposites. The change in resistivity was about 6 times larger for PANI–Ag nanocomposites and more than 4 times larger than for the PANI–Pt nanocomposites. To better understand the stronger response of PANI–Ag nanocomposites, Raman spectra were taken which indicated that charge was transferred to Ag, and to a lesser extent to Pt, by the nanofibers. That is, Ag acts as a dopant. Exposure to triethylamine reduces the charge transfer and therefore the doping, thereby amplifying the response to the analyte.