Different molecules have different ionization energies. Commercially available photo-ionization detectors (PIDs) emit light to ionize the molecules of interest. However, these PIDs require distinct lamps dependent upon the ionization energy required. In fact there are four types of lamps available, each with a different, fixed ionization energy. Due to limitation of available ionization energies, those detectors are only able to provide total volatile organic compounds (VOCs) concentration, and have no ability to provide any information on the types of VOCs.
Researchers at The University of Texas at Austin, in collaboration with INL - the International Iberian Nanotechnology Laboratory in Portugal, have developed a novel gas-sensing platform that allows measurement of inorganic gases and volatile organic compounds (VOCs) using a miniature low-cost sensor. The principle is based on gas ionization, but unlike commercially available PIDs that can only provide total volatile organic compound information, this technology can sweep the ionization energy, and therefore provide selectivity of detection. This capability to sweep is derived from use of a pyroelectric material, instead of a lamp to ionize the gas. Pyroelectric materials posses a unique characteristic, in that upon application of heating or cooling, an induced polarization of the material occurs leading to an increase in the surface charge density. This allows the novel sensor to be either tuned to a specific ionization energy, or to provide a scan of different energies. Tuning the ionization energy allows gradual ionization of different gases, therefore potentially enabling gas identification. It opens up significant opportunities for improving state-of-the-art low-cost gas sensing, and developing miniature sensors for applications in air quality, environmental monitoring, toxic gas detection, and other consumer-related products.
As a proof of concept study this technology has been used to detect acetone in ambient air conditions. Additional work is being done to further miniaturize and develop a process for future scalability.
Fig. 1: (A) Schematic showing the working methodology of the pyroelectric ionization-based gas sensor. (B) Plots demonstrating that increasing pyroelectric temperature will result in charge generation on the polarized surface of the crystal and subsequent ionization of the surrounding molecules.