Editorial Cite This: ACS Sens. 2019, 4, 780−780
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Challenges and Promises of Metal Oxide Nanosensors
ACS Sens. 2019.4:780-780. Downloaded from pubs.acs.org by 146.185.201.228 on 04/26/19. For personal use only.
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sensors via heavily doped oxide contact (DOI: 10.1021/ acssensors.7b00716). (2) New mechanistic studies that lead to potential solutions to overcome the existing issues of MOS. The combined theoretical and experimental efforts, and detailed spectroscopic and structural studies in the following papers provide new insights into gas sensing mechanisms. Zhou et al. studied crystal defect dependent gas-sensing mechanism of zinc oxide nanowire sensors (DOI: 10.1021/acssensors.8b00792). Yang et al. investigated the transformation of absorbed oxygen at zinc oxide with a combined thermal pulse method and density functional calculation (DOI: 10.1021/acssensors.7b00363). Degler et al. analyzed mechanism of a gold-loaded tin dioxide gas sensing materials (DOI: 10.1021/acssensors.6b00477). Tamvakos et al. carried out a combined experimental and theoretical study of nitric dioxide gas sensing mechanism of zinc oxide (DOI: 10.1021/acssensors.6b00051). (3) New applications that show superior performance of metal oxide nanosensors, such as in the following examples. Choi et al. applied catalytic Pt functionalized macroporous tungsten oxide nanofibers to measure breath pattern recognition (DOI: 10.1021/acssensors.6b00422). Güntner et al. published a paper on e-nose sensing of low-ppb formaldehyde in gas mixtures at high relative humidity for breath biomarker screening (DOI: 10.1021/acssensors.6b00008). The same group later demonstrated highly selective and rapid breath isoprene sensing (DOI: 10.1021/acssensors.7b00976). We welcome more manuscripts that address novel applications with new or existing materials, and perform validation under real or close to real conditions.
emiconductor metal oxide sensors (MOS) are attractive for gas sensing because they directly transduce chemical binding into an electrical signal (resistivity), making it easy to integrate into an electronic device. They are also easy to miniaturize, inexpensive to fabricate, and capable of detecting low concentration analytes (e.g., ppb-ppm), which are suitable for consumer products, including wearable devices. ACS Sensors has received a large number of manuscripts on MOS with many based on nano- and low-dimensional materials. The large surface-to-volume ratios of these novel materials promise high sensitivity (defined here as resistivity change for a given concentration change of analyte). However, high sensitivity does not automatically lead to low detection limit because the noise may also increase. One should also bear in mind that a lowering of the detection limit by 1 order of magnitude will often need to be matched with an improvement of other performance parameters, such as selectivity, and temperature and humidity tolerance. Several long-standing issues in MOS need to be overcome to develop a practical nano-MOS, including long-term stability caused by gas poisoning and other factors, and temperature and humidity effects. For applications that require quantitative results, calibration of the sensor is needed. This is not an easy task because it requires measuring the sensor’s response to analyte concentration, humidity, and temperature, separately. Considering that the response of a MOS to the three variables is often highly nonlinear, one must have sufficient data points to cover a reasonable dynamic range for each variable, which will result in a large number of measurements. For example, if we test 10 data points for each of the three variables, the total number of measurements would be 1000! A perfect sensor is impossible, nor is it needed, but we do need to have the appropriate performance for a specific application scenario. For example, reducing operation temperature is a nice energy saver, but it might be more meaningful for detecting flammable and combustible chemicals, or chemicals with low flash points. Similarly, humidity variability can be a headache, but a sensor that operates at, or close to, 100% relative humidity will be sufficient for breath analysis. We look forward to publishing more on major advances in metal oxide nanosensors, particularly works that cover the following key aspects: (1) Innovative solutions that solve the long-standing issues described above. The following works contributed to the solutions of quantitative sensing with nano-MOS. To address temperature dependence, Raghu et al. reported a temperature independent oxygen gas sensor based on titanium dioxide nanoparticles-grafted 2D nanoflakelets (DOI: 10.1021/acssensors.8b00544). Suematsu et al. developed an antimony-doped tin dioxide sensors that has high stability over humidity changes (DOI: 10.1021/acssensors.6b00323). Minimizing temperature and humidity will help simplify calibration. Miskell et al. addressed the problem of calibration of gas sensors in networks (DOI: 10.1021/acssensors.8b00074). Zeng et al. demonstrated long-term stability of oxide nanowire © 2019 American Chemical Society
Nongjian Tao, Associate Editor
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Arizona State University, Tempe, Arizona, United States
AUTHOR INFORMATION
Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS.
Received: April 2, 2019 Published: April 26, 2019 780
DOI: 10.1021/acssensors.9b00622 ACS Sens. 2019, 4, 780−780
