Nanostructured Spin Ladder Compound CaCu2O3 based Gas Sensor for the Detection of Volatile Organic Compounds
Authors: Lavanya Nehru 
Published: May 2020

Several volatile organic compounds (VOCs) are found in human breath and the concentrations of such VOCs are usually measured to be at sub-ppm level or even lower for healthy human beings. Abnormal concentrations of the breath VOCs are reported to correlate with unhealthy/injurious body/organ conditions; for instance, acetone gas for diabetes, trimethylamine for uremic patients and ammonia gas for renal disease. Hence, VOCs can potentially be used as disease-specific biomarkers for non-invasive early detection or monitoring from breath. Acetone can be produced via the fatty acid oxidation in diabetes and ketoacidosis lack of insulin. Excessive acetone circulating in the blood system is excreted from the lungs. Higher acetone concentration ranges from 1.7 ppm to 3.7 ppm could be detected in breath for those who are diabetic, while the breath of healthy human typically contains less than 0.8 ppm. Gas sensors with sub-ppm acetone detection capacity play an important role in the development of non-invasive monitors or early diagnosis of potential diabetic patients. Up to date, various gas sensors have been successfully developed to detect acetone by controlling the morphology of nanomaterials or introducing the noble metals into nanoparticles. Although, these sensors had achieved the purpose to detect acetone gas, the high operating temperature, higher-energy cost, and the long response time still limit their further applications in practice. Great effort has been made to improve that, by choosing novel material. In order to solve these problems, the present work will focus on the design and development of gas sensors based on new nanomaterials CaCu2O3 offer extremely large surface-to-volume ratio, and the possibility to modify their surface reactivity to attain high sensitivity at low concentration (ppt or lower) required for detection of acetone.

CaCu2O3 nanoparticles were synthesized by microwave irradiation method. The structural, morphological, electrical properties were studied by HRSEM, XRD and electrical measurements. The response of CaCu2O3 sensors to acetone at different operating temperatures is reported. It can be noted that the maximum of response to acetone observed at 200°C. The resistance change of the sensor to temperature change is quick and the baseline stabilization is attained in a brief time. The response of the sensor to acetone pulses is reversible and fast (τres ~ 5 seconds). Further, a considerable decrease has been observed in the recovery time (τrec ~ 20 seconds), which is another key advantage of this CaCu2O3.

The reproducibility and repeatability are other important factors for a acetone gas sensor. The cycling performance of the fabricated sensor at 200°C shows that the response to 100 ppm of acetone is the same when the measurements were repeated for 10 times consecutively, indicating the excellent reproducibility. Furthermore, the long-term stability of the sensor was also evaluated for many months, and the responses are nearly the same, demonstrating the good stability of the developed sensor.

CaCu2O3
nanorods have been prepared by microwave irradiation method and their gas sensing properties towards acetone and ethanol are investigated. All the fabricated sensors show reversible resistance changes while exposed to acetone. The gas sensing measurements of CaCu2O3 sensor exhibited high sensitivity and good selectivity towards acetone. Further, the fabricated sensor showed remarkable increase in sensor response and recovery times. The developed CaCu2O3 sensor is most promising candidate for highly sensitive and selective detection of acetone for medical applications.