Electrochemical Detection of Volatile Organic Biomarkers Using Next Generation Titania Nanotube Arrays

Analysis of volatile organic compounds (VOCs) from exhaled breath presents a potential non-invasive, label-free, and point-of-care (POC) medical diagnostic technique. Sensor detection of specific volatile organic biomarkers (VOBs) directly associated with a pulmonary or other disease presents itself as a facile method for early diagnosis.

Tuberculosis (TB) is arguably one of the most devastating infectious diseases in the world today. A major contributing factor to such a large number of cases is due to inadequate diagnostic methods for TB. Research has shown that various strains of the mycobacteria produce distinct gaseous volatile biomarkers that can be used as a methodology for detecting and identifying the mycobacterium.^1-2 Syhre and Chambers² found that Mycobacterium tuberculosis and Mycobacterium bovis cultures give off four specific volatile organic compounds (methyl phenylacetate, methyl p-anisate, methyl nicotinate, and o-phenylanisole).

In this work, we demonstrate the use of next generation titania nanotube arrays for the detection of TB VOB vapors. Functionalization of the nanotubular arrays is carried out in situ during electrochemical anodization to obtain next generation titania nanotube arrays.³ Preliminary studies (electrochemical and density functional theory) indicate Co(II) to have favorable binding affinity with TB VOBs. Amperometric testing results show that cobalt (II) functionalized TiO₂ nanotubes are capable of detecting methyl nicotinate and methyl p-anisate when derived from chemical mimics dissolved in ethanol and delivered to the sensor by bubbling N₂ gas. Results also show that the sensor response to ethanol and humidity alone is minimal as well as to other VOCs commonly found in human breath (e.g., acetone, ethanol, benzene, and phenol) when compared to exposure to biomarkers under the same testing conditions. The concentration of the VOB vapor reaching the sensor was estimated to be ~2 mM.

Under conditions previously described, in situ functionalized titania nanotubes shows a greater sensor response (80~100 μA) with drastically faster response and recovery (a few to 10’s of seconds) compared to titania nanotube functionalized by ion exchange method (6~10 μA signal and 100’s of seconds response).⁴ The in situ functionalized synthesis approach not only demonstrates a higher and quicker sensor response than previous results, but also eliminates a synthesis step and ensures greater reproducibility.

References:

1. Phillips, M.; Cataneo, R. N.; Condos, R.; Ring Erickson, G. A.; Greenberg, J.; La Bombardi, V.; Munawar, M. I.; Tietje, O., Volatile biomarkers of pulmonary tuberculosis in the breath. Tuberculosis 2007, 87 (1), 44-52.

2. Syhre, M.; Chambers, S. T., The scent of Mycobacterium tuberculosis. Tuberculosis 2008, 88 (4), 317-23.

3. Smith, Y. R.; Sarma, B.; Mohanty, S. K.; Misra, M., Formation of TiO2-WO3 Nanotubular Composite via Single-Step Anodization and its Application in Photoelectrochemical Hydrogen Generation. Electrochem. Comm. 2012, 19, 131-134.

4. Bhattacharyya, D.; Smith, Y. R.; Misra, M.; Mohanty, S. K., Electrochemical Detection of Methyl Nicotinate Biomarker Using Functionalized Anodized Titania Nanotube Arrays. Mater. Res. Express Accepted-In press.