Light Activated Surface Acoustic Wave Investigations of Photoconductive Polymer Films for DMMP Detection

We report the light activated surface acoustic wave (SAW) investigations of DMMP (dimethyl methylphosphonate – safe simulant of warfare agents) sensing at low interaction temperatures based on photoconductive polymer films such as: RR-P3HT (Regio-Regular Poly-3-hexylthiophene) and SilPEG1.4. The sensor structures were composed of 205 MHz quartz dual delay lines and a thin (~50 – 100 nm) polymer films created by means of a simple spray coating method. The investigated polymer films showed a significantly enhanced sensitivity towards low DMMP concentrations in the air (1.5, 2 and 3 ppm) under the light illumination, especially in the wavelength range of a yellow (~590 nm) and blue (~445 nm) laser LED’s and LED’s sources. The relative sensitivity increase (RSI), which is the ratio of sensor structure response with and without light activation is between ~275 for SilPEG1.4 to even ~420 for RR - P3HT at a blue LED activation and 2 ppm of DMMP in air. Such substantially enhanced response can be interpreted as an acoustoelectric sensitivity (AES) increase. This assumption was confirmed by an additional resistance method, i.e. the electrical surface sheet conductivity of the investigated polymer films is significantly increasing under a light illumination, especially for a yellow and blue wavelenghts, causing the shifting of the sensor structure “work point” towards the higher AES values.