Performance characteristics of gas-phase microsensors will determine the ultimate utility of these devices for a wide range of chemical monitoring applications. Considerable effort has led to electronic nose devices that utilize multiple cross-selective sensing elements and varied transduction mechanisms. Commonly employed chemiresistor elements are quite sensitive to selected target analytes, and relatively new methods have increased the selectivity to specific compounds, even in the presence of interfering species. In this work, we have directly focused on determining whether purposefully driven temperature modulation can produce faster sensor-response characteristics, which could enable measurements on a broader range of applications involving dynamic compositional analysis. We examined the effect on response speed to four analytes (methanol, ethanol, acetone, 2-butanone) of varying the oscillating frequency (semi-cycle periods of 20 ms to 120 ms) for a bi-level temperature cycle applied to a single In2O3 chemiresistive sensor based on a microhotplate platform. It was determined that the fastest operation (~ 9 s), as indicated by a 98% response metric, occurred for a period of 30 ms, and that responses under such modulation were dramatically faster than for isothermal operation of the same device (> 300 s). The short dwell-time modulation between 150 °C and 450 °C exerts kinetic control over transient processes, such as adsorption, desorption, diffusion, and reaction phenomena that are important for charge transfer occurring in the transduction process and the observed response times. Moreover, we also demonstrate that the fastest operation is accompanied by excellent discrimination within a challenging 16-category recognition problem (consisting of the 4 analytes at 4 separate concentrations).
Citation: Analytical Chemistry
Pub Type: Journals
Metal-oxide gas-phase sensors, Temperature modulation, Optimization, Gas Discriminatin and Quantification