Surface acoustic wave (SAW) sensors are widely employed for detecting dimethyl methylphosphonate (DMMP, a simulant of the chemical warfare agent sarin) due to their wireless and passive monitoring capability, digital output, and cost-effectiveness. Zirconium dioxide (ZrO2) nanoparticles are considered one of the most promising sensing materials for DMMP detection owing to their unique and strong surface interactions with phosphorus-containing compounds, as well as their excellent chemical and thermal stability. However, the practical deployment of ZrO2 SAW sensors faces significant challenges, as atmospheric humidity severely degrades their performance, causing substantial sensitivity drift and even polarity reversal. This work reports a strategy involving the modification of ZrO2 nanoparticle surfaces with hydrophobic functional groups (-Si(CH3)3). This approach successfully transformed the inherently superhydrophilic ZrO2 material (water contact angle, WCA = 19°) into a hydrophobic state (WCA = 136°). For SAW sensors based on this hydrophobized ZrO2, the initial frequency drift induced by humidity was suppressed by 92.6 at 85% relative humidity (RH). More importantly, across the dynamic humidity range of 20-85% RH, the DMMP response remained stable at approximately -325 Hz/ppm (fluctuation 2 SAW sensors, whose responses fluctuated drastically between -1030 Hz/ppm and +1141 Hz/ppm under identical conditions. The mechanisms underlying the humidity-induced sensitivity drift in ZrO2 SAW sensors were elucidated using in situ infrared absorption spectroscopy and X-ray photoelectron spectroscopy techniques. This study not only provides a straightforward strategy for imparting hydrophobicity to ZrO2 but also offers novel insights for addressing the issue of frequency drift in SAW sensors caused by atmospheric moisture.
Guo et al. (Wed,) studied this question.