Ni-Based Tantalate Sensing Electrode for Fast and Low Detection Limit of Acetone Sensor Combining Stabilized Zirconia

Abstract

Introduction Acetone (CH3COCH3) is a colorless transparent liquid with a special pungent smell, which is categorized as important member of volatile organic compounds (VOCs). It offers many important information in early medical diagnosis of diabetes. In exhaled breath of healthy human, the average concentration of acetone is 0.3-0.9 ppm, which is far below lowest detection limit of 1.8 ppm in exhaled breath of diabetes patients. Taking into consideration of the practical detection demand for healthy medical diagnosis, the highly performance gas sensor is to be expected. Here, a stabilized zirconia (YSZ) based acetone sensor based on mixed potential sensing mechanism was fabricated using NiTa2O6 sensing electrode (SE) calcinated at 1000 °C. The NiTa2O6 sensing material was characterized by TG/DSC, XRD, SEM, Raman and XPS measurement. The gas sensing performance of developed sensing device demonstrated that the sensor based on NiTa2O6-SE displayed low detection limit of 200 ppb acetone and rapid response and recovery times of 9 s and 18 s to 2 ppm acetone at 600 °C. Between the response value to wide concentration range of 0.2-200 ppm acetone and the acetone concentration logarithm for the developed sensor presented piecewise linear function. The fabricated acetone sensor also possessed good wet fastness, reproducibility and stability of 20 days, portending great potential in aspect of low and high acetone concentration detection. More importantly, the solid electrolyte type acetone sensor utilizing NiTa2O6-SE open up a new possibility for noninvasive diagnosis of diabetes through detecting exhaled breath of healthy people and diabetes patients. Results and Conclusions The operating temperature affects the activation degree for the electrochemical reaction and adsorption and desorption process of sensing electrode, which results in the change of gas sensing performance for the fabricated sensor. Thus, the response and recovery curves of the sensor utilizing NiTa2O6-SE sintered at 1000 °C to 50 ppm acetone at temperature range of 475-650 °C are tested. Accordingly, 600 °C was selected as the optimal operating temperature to investigate the corresponding sensing characteristics of present device. In the acetone concentration range of 0.2-200 ppm, the sensor exhibited good response and recovery characteristics and the response signal increased gradually with the increase of acetone concentration. Notably, a spike appears at larger tested gas concentration, which is also observed by other reported works [1, 2, 3, 4]. Therefore, to avoid disturbance of the spike and to render certain the accuracy of sensing performance, the exposed time of 2.5 min in acetone gas and exposed time of 3.5 min in air is performed. The potential values at the last second were used for calculation of the response. The low detection limit of the sensor was 200 ppb acetone and the response and recovery times to 2 ppm acetone were 9 s and 18 s, respectively. The ΔV of the sensor to 0.2–2 ppm and 2-200 ppm acetone and concentration logarithm of acetone displayed linear relationship at 600 °C and the sensitivity of the sensor to 0.2-2 ppm and 2-200 ppm acetone were -11 and -27 mV/decade, which demonstrated the good acetone detection ability in aspects of lower and higher concentration. Comparison of the acetone sensing performances of developed sensor in this work and those of solid electrolyte sensing devices reported in literatures. More importantly, the present sensor attached with NiTa2O6-SE possessed significant advantages of low detection limit of acetone and response or recovery speeds in the lower acetone concentration, indicating the good potential alternative device for effectively monitoring acetone.To evaluate the possibility of the present sensor to be a practical acetone device, clinical detection for acetone biomarker in real exhaled breath of healthy volunteers and diabetes is further performed based on the sensor attached with NiTa2O6-SE. Here, the exhaled breath samples are taken from three healthy volunteers and diabetes patients. The blood ketone level of three diabetes patients is 0.6 mmol/L, 2.0 mmol/L and 6.3 mmol/L. The sensor exhibited low response signal and relatively good consistence to exhaled breath of three healthy volunteers. However, the response signal of the sensor to exhaled breath of three diabetes patients apparently higher than that of healthy peoples. Furthermore, the response value of the sensing device enhanced gradually with the increase of blood ketone levels of three diabetes patients. In this case, the difference in response value between diabetes and healthy people becomes more obvious, namely, the sensor can well distinguish between diabetic patients and healthy people. Accordingly, the developed acetone sensor attached with NiTa2O6-SE possessed good possibility to diagnosis diabetes.