Effects of dimensions on the sensitivity of a conducting polymer microwire sensor

It is commonly considered that the sensitivity of a microsensor increases with its increasing surface-to-volume ratio. However, it is not exactly clear how the surface-to-volume ratio affects the sensitivity of a conducting polymer microsensor. The change in any of the three geometrical dimensions (i.e., length, width and thickness) of a microsensor changes the surface-to-volume ratio. In designing a microsensor of desired sensitivity, it is important to know the effect of each dimension on the sensitivity for properly defining the sizes and shapes of the microsensor. As such, in this work, we have investigated the effects of each individual dimension on the sensitivity of a conducting polymer microwire sensor. Polypyrrole (PPy) and Poly (3,4-dimethlydioxythiophene) poly(styrenesulfonate) (PEDOT–PSS) microwire sensors of different dimensions were fabricated using an intermediate-layer lithography (ILL) method. They were further employed to detect methanol and acetone vapors at concentrations in the range of 0.6–7.1 parts per thousand (ppt). The corresponding three relationships between the three geometrical dimensions and the sensitivities were found using a statistical program, SAS. From the point view of surface-to-volume ratio, the thickness should affect the sensitivity much more than the other two dimensions. However, the three relationships indicate that the effects of the three geometrical dimensions on the sensitivity of a microwire sensor vary with the conducting polymer materials and the targets to detect. In other words, which dimension has more effects on sensitivity is case-dependent. Results presented in this work can be potentially used to aid in the design of conducting polymer microwire sensors of high sensitivity.