(372f) Application of Hydrophobic-Polymer Coated TiO2 Nanotube Electrochemical Sensors in Humid Environments

In this work, the effect of a hydrophobic, gas permeable polymer coatings on a vapor-based electrochemical sensor is investigated. This technology will allow volatile organic compounds (VOCs) to be sensed more accurately in humid environments, such as those found in human breath, agricultural settings, and industrial processes. In this case, cobalt-functionalized titanium dioxide nanotube array (Co-TNA) sensors were coated with a thin layer of cross-linked polydimethylsiloxane (PDMS). These sensors are traditionally used uncoated in the rapid detection of mycobacterium tuberculosis in human breath. This is achieved by detecting several different VOC biomarkers produced by the mycobacterium, the most important of which is methyl nicotinate. The functionalized sensors are known to be sensitive to humidity causing issues with signal to noise ratio during operation. This is thought to be primarily due to water vapor condensing on the surface of the sensor, drawing cobalt ions away from nanotubes and making the signal less distinguishable than in dry air. A hydrophobic, gas permeable coating can be used to bypass this issue. PDMS is commercially available, its interactions are well known and it can easily be coated onto surfaces before it is fully crosslinked, making it an ideal candidate. The thickness and chemical transport properties of the polymer can be changed easily by diluting the PDMS in toluene before dip-coating and varying the amount of cross-linker added. Preliminary testing has shown that thinner coatings of PDMS allow the VOC (in this case methyl nicotinate) to reach the sensor surface more quickly than thicker coatings, as expected. For example, a dilution of 20 g of PDMS in 20 mL of toluene showed a response to the VOC after 20 min of exposure, while the same amount of PDMS in 40 mL of toluene responded after only 12.5 min. Methods for applying these thin coatings, transport properties of the VOC through the coating and the effect on sensor response will be presented. This work has applications in biomedical diagnostics, environmental/food safety, and water monitoring.