(Invited) Enhancing Reliability of Gas Sensors with New Design Rules for Sensing Materials and Transducers (2020)

Contemporary gas monitoring scenarios for industrial safety, environmental surveillance, medical diagnostics, personal wellness, and other applications demand sensors with higher accuracy, enhanced stability, and often lower power; all in unobtrusive formats and at low cost [1-3]. Unfortunately, available sensors based on traditional detection principles often have not only inadequate accuracy and stability but also have relatively high power demands, pushing the limits of existing detection concepts where we are reaching their fundamental performance limits. These limitations of available sensors drive the innovative designs of new generation of sensors. We are focusing on development of new principles of gas sensing based on multiparameter signal excitation and detection resulting in a new generation of gas sensors based on the multivariable response principles. Design criteria of these individual sensors involve a sensing material with multi-response mechanisms to different gases and a multivariable transducer with independent outputs to recognize these different gas responses. In our talk, we will discuss our different sensor types that operate over the electromagnetic spectrum ranging from the radio-frequency to microwave and to optical regions. We will discuss new performance capabilities of the developed sensors using two broad examples of our recent developments. In the first example, we will discuss our multivariable sensors in the radio-frequency and microwave spectral regions [4-6]. We are implementing impedance spectroscopy and diverse types of sensing materials and transducers with the goals of improving gas-selectivity of our sensors and rejection of interferences. Examples of our sensing materials in these spectral regions include conjugated and dielectric polymers, ligand-functionalized metal nanoparticles, metal oxides, and carbon allotropes. Examples of our transducers include resonant and non-resonant structures. In the second example, we will discuss our multivariable sensors in the optical spectral region [7-11]. We are implementing our bio-inspired three-dimensional nanomaterials with the visible-light reflectance or transmittance measurements with the goals of improving gas-selectivity of our sensors and enhancing sensor stability. Examples of our sensing materials operating in the optical spectral region include polymeric and inorganic nanostructures functionalized based on our design rules for multi-gas detection using individual sensors. Our developments resulted in sensors with previously unavailable performance characteristics in wearable, stationary, airborne and other formats where our multivariable sensors independently quantify up to four individual gases in complex mixtures, reject interferences with up to 2,000,000-fold overloading in concentrations over the analytes, and enhance sensor-response stability. Such performance characteristics are attractive when selectivity advantages of classic gas chromatography, ion mobility, and mass spectrometry instruments are canceled by requirements for no consumables, low power, low cost, and unobtrusive form factors for Internet of Things, Industrial Internet, and other applications. We will conclude with a perspective for future needs in fundamental and applied aspects of gas sensing and with the 2030 roadmap for ubiquitous gas monitoring. [1] Bogue, R. Towards the trillion sensors market. Sensor Rev. 34 , 137-142 (2014). [2] Alexander, M., Bernhart, W., Rossbach, C. &amp; Nölling, K. Smart Strategies for Smart Sensors . (Roland Berger GMBH, 2017). [3] Potyrailo, R. A. Ubiquitous wearable and disposable chem-bio sensors: markets demands and innovative technology solutions . (Sensors Expo &amp; Conference, San Jose, CA, June 26-28, 2018). [4] Potyrailo, R. A., Surman, C., Nagraj, N. N. &amp; Burns, A. Materials and Transducers Toward Selective Wireless Gas Sensing. Chem. Rev. 111 , 7315–7354 (2011). [5] Potyrailo, R. A. Multivariable sensors for ubiquitous monitoring of gases in the era of Internet of Things and Industrial Internet. Chem. Rev. 116 , 11877–11923 (2016). [6] Potyrailo, R. A. Toward high value sensing: monolayer-protected metal nanoparticles in multivariable gas and vapor sensors. Chem. Soc. Rev. 46 , 5311-5346 (2017). [7] Potyrailo, R. A. et al. Morpho butterfly wing scales demonstrate highly selective vapour response. Nature Photonics 1 , 123-128 (2007). [8] Potyrailo, R. A. et al. Discovery of the surface polarity gradient on iridescent Morpho butterfly scales reveals a mechanism of their selective vapor response. Proc. Natl. Acad. Sci. U.S.A. 110 , 15567–15572 (2013). [9] Potyrailo, R. A. et al. Towards outperforming conventional sensor arrays with fabricated individual photonic vapour sensors inspired by Morpho butterflies. Nature Commun. 6 , 7959 (2015). [10] Potyrailo, R. A., Karker, N., Carpenter, M. A. &amp; Minnick, A. Multivariable bio-inspired photonic sensors for non-condensable gases. J. Opt. 20 , 024006 (2018). [11] Potyrailo, R. A. et al. Multi-gas sensors for enhanced reliability of SOFC operation. ECS Transactions 91 , 319-328 (2019).