Ratiometric info-chemical communication system based on polymer-coated surface acoustic wave microsensors

A novel ratiometric info-chemical communication system has been developed that is based upon an array of four surface acoustic wave (SAW) resonator microsensors operating at a frequency of 262 MHz and under ambient conditions. The info-chemical mixtures were generated by a micro-evaporator and transported to the SAW sensors inside a flow chamber. Binary mixtures of 3-methylbutan-1-ol and ethyl acetate were used to demonstrate the principle of encoding and decoding different ratios of volatile info-chemicals in this system. The resonant frequencies of the four polymer-coated SAW sensors and the associated reference (uncoated) SAW sensors were used to determine differential responses corresponding to the different ratiometric mixtures of the info-chemicals. The SAW sensors were spray coated with four different stationary phase polymer compounds, namely polycaprolactone, polyvinylcarbazole, polystyrene-co-butadiene, and polyethylene-co-vinylacetate. Principal components analysis was performed on both steady-state and dynamic features extracted from the sensor responses. Our results show clear linear separability of the different chemical ratios as distinct clusters in multi-variate space. In conclusion, we believe that this is the first demonstration of the encoding, transmitting, and decoding ratiometric information using a system based upon an array of SAW-based microsensors. This novel info-chemical communication system, based upon fixed ratios, transmits chemical information over distances that would otherwise be impossible using absolute concentrations.