Inducing analytical orthogonality in tungsten oxide-based microsensors using materials structure and dynamic temperature control

The influence of material structure and dimension on the chemical sensing performance was investigated as a function of sensor operating temperature. Polycrystalline tungsten oxides (WO₃) were prepared both as nanowires of different diameters (d ≈ 100 nm, 175 nm; l = 4-5 μm) using a template-directed electrodeposition process, and as a continuous film through thermal decomposition of peroxytungstate solution. The WO₃ materials were integrated with microscale conductometric platforms featuring millisecond dynamic temperature control up to 500 °C. The nanowires and film were assessed for efficacy as transducers in gas-phase chemical sensors using these platforms, both in a fixed-temperature operating mode and in a dynamic pulsed-temperature operating mode. Statistical analysis of the tungsten oxide chemiresistor responses to analytes at varied operating temperatures revealed that orthogonal information can be obtained from stoichiometrically similar materials; the differences were exaggerated by probing the sensor responses with different dynamic temperature programs. We conclude that nanowire sensors yield non-redundant analytical information with respect to their complementary film-based sensor. These results demonstrate that as sensors move to nanoscale structures, unique interactions will differentiate the materials and the devices' performance from their microscale counterparts.