Enhanced sensitivity of SAW based ammonia sensor employing GO-SnO2 nanocomposites

A GO-SnO2 nanocomposites coated surface acoustic wave (SAW) device is proposed for sensing ammonia with extremely low concentrations. The GO-SnO2 nanocomposites with diameters of ∼4.3 nm was controllably synthesized in a hybrid solution system of oleic acid (OA) and oleylamine. We revealed that the SnO2 nanocrystals were uniformly immobilized on the GO surface and exhibited porous structures through the characterizations of TEM, SEM, XRD, and Raman. The gas adsorption in GO-SnO2 modulates the SAW propagation velocity, and the corresponding changes in phase/frequency can be collected as the sensing signal. A 200 MHz SAW device with the delay-line pattern was prepared by using the lithograph technique on the Y35°X quartz substrate. The GO-SnO2 was deposited on the SAW device by drip-coating, and the device was integrated in the phase detection circuit to build the ammonia sensor and experimentally characterized. Very low detection limit of 40 ppb and a high sensitivity of 0.098 mV/ppb with a fast response of less than 16.4 s were achieved at room temperature (25 °C). In addition, the developed sensing device exhibited excellent selectivity and stability, and the effects of ambient humidity and temperature on the sensing performance were also investigated.