Tetracosane Functionalized Nanostructure Titanium Oxide Sensors for Screening Pneumonia from Breath

Volatile organic compounds (VOCs) are present in the environment and human bodies. Ethanol, acetone, and isoprene are examples of VOCs in the healthy human body, specifically in breath¹. Diseases such as pneumonia have VOCs associated with it in breath². Pneumonia is the cause of 16% death of children under five globaly³. In the US, pneumonia is the first common reason of hospitalization in children and the second common reason for adults’ admission after women giving birth³. Therefore, there is a need for an inexpensive, noninvasive, and quick pneumonia screening method that can simply be performed in clinics on the first patient visit. Patients with pneumonia have been shown to have breath profiles that include unique VOCs that derive from the biological pathogen and perturbations in the health of a patient. The presence of heptane and increase in the amount of ethanol are examples of VOCs associated with pneumonia². Developing a device to measure the presence of these VOCs in breath could be used as a screening method to detect pneumonia. In this work, a suitable molecule is functionalized on a titanium oxide platform to give an electrochemical response in the presence of pneumonia VOCs.

The sensor synthesis process consists of anodization of titanium oxide nanotubes and annealing the anodized self-ordered nanotubes under oxygen. Titanium oxide nanotubes provide an adequate conductivity and have an amorphous surface area suitable for external coatings. As mentioned earlier, ethanol is at a higher concentration in the breath of patient’s suffering from pneumonia compared healthy human’s breath². Titanium oxide nanostructure at given voltages responds to the presence of ethanol by showing current changes. But for the purpose of detecting pneumonia, a more specific sensor is needed. To design a sensor that also responds to heptane, titanium oxide nanotubes were functionalized with tetracosane. Tan et al.[4] showed that when alkane gets mixed with tetracosane on a conductive surface. At a constant voltage of 1.5V, the tetracosane functionalized titanium oxide sensor performs as a chemiresistive sensor. It responds to heptane and ethanol in the gas phase by showing current changes. Table (1) shows the current response for a tetracosane functionalized titanium oxide sensor to ethanol, heptane and humid air exposure. Due to the presence of humidity in the human breath, the sensor was exposed to controlled humid samples. When heptane, humid air, and ethanol were exposed to the functionalized sensor, the current increased to different magnitudes (figure 1). Room air was bubbled through a solution of the VOC of interest and exposed to the sensor that was placed on PCB board. The current change magnitude and the response time of the sensor varied for each exposure. The sensor’s response to humid air and ethanol was instant, whereas the coated tetracosane sensor responded to heptane exposure after a minimum of 40 seconds. The sensor’s current change to ethanol exposure was a minimum of three orders of magnitude higher than heptane in the first 100 seconds of sample exposure. The tetracosane functionalized sensor shows a different response to each heptane, ethanol, and humid air in gas phase. The sensor’s response to different concentrations of heptane and ethanol separately and mixed together in mimicked breath samples will be presented.

References:

[1] J. D. Fenske and S. E. Paulson, “Human breath emissions of VOCs,” J. Air Waste Manag. Assoc., vol. 49, no. 5, pp. 594–598, 1999.

[2] R. Schnabel et al., “Analysis of volatile organic compounds in exhaled breath to diagnose ventilator-associated pneumonia,” Sci. Rep., vol. 5, no. July, pp. 1–10, 2015.

[3] N.A., “Top 20 Pneumonia Facts 2018,” Am. Thorac. Soc., p. 2018.

[4] Jiunn-Liang Tan; Zheng-Xin Yong; Chong-Kin Liam, Using a chemiresistor-based alkane sensor to distinguish exhaled breaths of lung cancer patients from subjects with no lung cancer. Journal of Thoracic Disease 2016, 10.2103