Chemical Sensing

A sensor is a device that measures a chemical or physical event and produces a corresponding signal that can be read by an observer or an instrument. Broadly, sensors can be divided into physical (e.g., temperature, pressure, magnetic field) and chemical (e.g., NOx, H2S) sensing devices. The driving forces for advancement in sensing technology include reducing cost, reducing size, improving performance, realizing new functionalities, and achieving autonomous self-powering devices, as a part of Internet-of-Things (IoT). Our research in this area is currently focused on chemical sensing, where there is a strong need for miniaturized, low-power gas sensors that can be deployed in wireless applications for improved environmental protection, energy efficiency, public health, and safe and efficient operation of many industrial processes. We leverage the advances made in micro-/nanofabrication technologies and innovations in nanomaterials to help address this need. Current Research:
  • Low-power microheater platform for gas sensing (Sikai, Yong)
  • Novel MOF-based nanomaterials for enhanced chemical selectivity (David)
  • Colorimetric CO2 sensing for personal air-quality monitoring (Adrian)

Recently Completed Projects

Novel Hierarchical Metal Oxide Nanostructures for Conductometric Gas Sensing

Semiconducting metal oxides have been extensively studied as sensing materials for conductometric gas sensors. Nanostructured metal oxides integrated with miniaturized heating elements have been shown to exhibit particularly high sensitivity while maintaining low power consumption. However, the incorporation of nanostructured metal oxide films onto miniaturized heater-based sensing platforms commonly suffers from uncontrollability in film thickness and microstructure, which reduces sensor performance and fabrication reproducibility. We have developed a controllable and flexible method for the localized in situ growth of ordered metal oxide hollow sphere 2D array directly on a microfabricated heater platform, which allows much improved controllability in the sensing material morphology and coverage. A resulting SnO2 hollow sphere-based microsensor showed high sensitivity and selectivity toward formaldehyde and extremely fast response and recovery. Furthermore, this method can be used to fabricate microsensors using a variety of metal oxides, including combinations of different metal oxides in multi-shelled hollow sphere arrays, for enhanced sensitivity and tunable selectivity.

Conductometric Gas Sensing Behavior of Aerogels based on Two-dimensional Materials

Aerogels have attracted significant attention in recent years due to their extremely low density, high surface area, low thermal conductivity, weak dielectric permittivity, and high stability. For gas sensing applications, two-dimensional materials offer the highest possible surface area for gas interaction, leading to high sensitivity. However, when materials are integrated into a sensor device, the surface area is limited by the device footprint. Assembling 2D sheets into 3D assemblies, like aerogels, provides a low-density material with large number of interconnected pores that increases the surface area available in a given footprint while maintaining the properties of the few-layer sheets. We synthesized several aerogels (based on graphene and 2D-transition metal dichalogenides), integrated them with our low-power microheater platform, and reported them to be an effective approach towards low-power detection of several combustible and toxic gases.