Analyte-Dependent Sensing Mechanisms: The Fabrication and Characterization of a 32-Channel Array of SWCNT-TF Chemiresistive Sensors

In this article, we discuss the fabrication and characterization of a 32-channel array of single-walled carbon nanotube thin film (SWCNT-TF) chemiresistor sensors. By simply varying the SWCNT-TF device geometry from a length-to-width (L/W) ratio of 1.5:1-15:1, the device switching characteristics were tuned, which provided a unique platform for the investigation of analyte-dependent sensing mechanisms. Our results indicate that the dominant mechanisms for pH sensing and M13 bacteriophage sensing are distinctively different. The percentage resistance change (ΔR/R0) of the SWCNT-TF devices in response to pH change can be well explained by chemical doping due to OH^-/H⁺ adsorption on nanotubes. In contrast, electrostatic gating was found dominant in the sensing of M13 bacteriophage, where a decrease in the double-layer capacitance by M13 captured on the sensor´s surface significantly reduced the overall SWCNT-TF conductance. The of all devices was found to exhibit a logarithmic dependence on M13 concentration. An experimental detection limit of 0.5 pM M13 was demonstrated on all devices, with a theoretical detection limit down to the fM range on high-aspect-ratio (15:1) devices. Using M13 bacteriophage as a model virus, this study demonstrated the potential of SWCNT-TF chemiresistor sensors for real-time electrical virus detection, provided better understanding of sensing mechanisms, and outlined the importance of film/device geometry in the optimization of sensitivity and reproducibility.