Improved Gas-Phase Detection of Volatile Organic Compounds Using a Solid-State Conductive Polymer Electrolyte

Abstract

Rapid screening of tuberculosis by evaluation of associated volatile organic compounds (VOCs) in breath has been shown to be a promising technology that is significantly faster and more convenient than traditional sputum culture tests. Methyl nicotinate and methyl p-anisate have been isolated as specific biomarkers for the mycobacterium tuberculosis, as they are not found in high concentrations in ambient air or the breath of healthy patients, but should be readily present in all patients with active TB. These VOCs can be electrochemically detected using a solid-state sensor based on metal-functionalized 3D titanium dioxide nanotube arrays (TNAs), as shown by Bhattacharyya et. al. [1]. This chronoamperometric method uses a two-electrode system, in which the pure titanium back of the sensor functioned as both the counter and reference electrode, meaning that the applied current is highly dependent on the resistance of the nanotubes and difficult to reproduce from sensor to sensor. This work will discuss two improvements to the current method: 1) a move to a three-electrode system using a solid electrolyte, and 2) potential scanning electrochemical methods used for detection. To improve reproducibility and specificity of the sensor, the platform has been modified to use a solid-state, conductive electrolyte in order to create a gas phase three-electrode system. A conductive polymer of known resistance is used to separate the functionalized TNA from the silver-painted counter and reference electrodes. Doing this ensures more consistent interactions with the analyte of interest between sensors. In addition to the electrode changes, new scanning potential methods such as cyclic voltammetry (CV) and square wave voltammetry (SWV) have shown promise in detecting the analytes more specifically than chronoamperometry. For example, running cyclic voltammetry using cobalt functionalized sensors shows a reduction peak at about -0.5 V vs a silver quasi-reference electrode when exposed to methyl nicotinate vapor. Results comparing different electrochemical methods and specific responses to the biomarkers will be presented. [1] D. Bhattacharyya, Y. R. Smith, S. K. Mohanty, and M. Misra, “Titania Nanotube Array Sensor for Electrochemical Detection of Four Predominate Tuberculosis Volatile Biomarkers,” J. Electrochem. Soc., vol. 163, no. 6, pp. B206–B214, 2016.