Selective Detection of CO2 and H2O Dual Analytes Through Decoupling Surface Density and Shear Modulus Based on Single SAW Resonator

The detection of carbon dioxide (CO
₂
) and water molecules (H
₂
O) is of great interest because they play an important role in the fields of industry, agriculture, climate and medical treatment. However, both experimental studies and engineering applications indicate that most CO
₂
sensors suffer from selectivity problems in high humidity. Herein, we detect concentrations of CO
₂
and H
₂
O simultaneously through decoupling surface density and shear modulus under negligible effect of electric conductivity based on a surface acoustic wave (SAW) resonator at 221 MHz. The SAW-based sensor demonstrates a small measurement error of ~ 65 ppm in CO
₂
and ~ 1.2% RH in H
₂
O. The sensor also shows excellent short-term stability of 0.8 kHz. Besides, this general method that using a single SAW resonator to detect two analytes selectively will be useful for other resonator-based sensors.