Light-activated SAW sensor structures with photoconductive polymer films for DMMP detection

Abstract

We report the light-activated surface acoustic wave (SAW) investigations of DMMP (dimethyl methylphosphonate) sensing based on photoconductive polymer films such as: (rr)P3HT (regio-regular Poly-3-hexylthiophene) and SilPEG1.4. These SAW sensor structures were composed of ∼205 MHz quartz dual delay lines with a novel switchable digital generator set-up and a thin (∼50–100 nm) polymer films created by means of a simple spray coating method. The white light, low power laser LED (blue, green, red) and seven LED’s sources were applied for light activation of the SAW structures. The relative sensitivity increase (frequency shifts in light vs. the non activated state) at 2 ppm of DMMP is ∼275 for SilPEG1.4 with a blue LED (∼460 nm), to even ∼340 for (rr)P3HT with a yellow LED (∼585 nm) activation. This last structure has also acceptable stability and repeatability with the limit of detection ∼133 ppb, the response/recovery times ∼5–100 s / ∼240 s, and sensitivity coefficient ∼1.013 kHz/ppm in ppb ranges. The observed substantially enhanced light-activated SAW sensitivity should be interpreted in category of the acoustoelectric interactions, because the acoustoelectric parameter, estimated by resistive transducer results, has the greatest value for a yellow and blue LED light illumination.