Carbon dioxide, or CO₂ gas, is an important atmospheric gas in the environment. An increase in CO₂ concentration affects environmental damage. On the other side, CO₂ concentration increases from year to year. In line with this, there is a need to develop a measurement system of CO₂ concentration with good performance. Thus, this study aims to develop a quartz crystal microbalance (QCM)-based CO₂ sensor using titanium dioxide nanoparticles and to identify the response and reversibility levels. For this purpose, this study used five sensors with different thicknesses: Q₁, Q₂, Q₃, Q₄, and Q₅, to identify the response and reversibility responses. The results show that the sensors had a frequency shift of 5.14 kHz (Q₁), 5.19 kHz (Q₂), 5.70 kHz (Q₃), 5.78 kHz (Q₄), and 6.05 kHz (Q₅). The response times are 80.1 s (Q₁), 82.8 s (Q₂), 84.6 s (Q₃), 85.5 s (Q₄), and 247.5 s (Q₅). The frequency shifts and the response times indicate that Q₅ has the best response for CO₂. All sensors have fast recovery times, 10.8 s to 21.6 s. It can be concluded that the developed sensors have good response times, recovery times, and reversibility levels for CO₂ gas detection. This sensor can be used as an alternative to a CO₂ gas concentration measurement system, providing a novel and rapid detection method and fast recovery time.