One class of biomarkers that is known to have associations with certain diseases, and yet has found limited use as a diagnostic tool is volatile organic biomarkers (VOBs). From a healthcare standpoint, sensing and detection of VOBs from the breath is important for early diagnosis of several pulmonary diseases, including tuberculosis, whose distinct biomarkers have been successfully identified by researchers using mass spectroscopy. Time of detection, cost, equipment portability, and performance have been identified as some of the major roadblocks in the development of a suitable device for point-of-care (POC) detection of tuberculosis (TB). In this study, we demonstrate the use of metal functionalized TiO2 nanotubes array (TNA) based robust sensing platform for rapid electrochemical detection of the four prominent TB biomarkers viz. methyl nicotinate, methyl p-anisate, methyl Phenylacetate, and o-phenylanisole.
Solid-state TiO2 nanotube array has demonstrated to be a promising sensing platform for VOCs detection. Highly ordered TNA were synthesized through electrochemical anodization, and functionalized separately with cobalt and gold, which were determined as leading frontrunners for efficient binding with the VOBs. Cobalt functionalization was first achieved using the incipient wetting impregnation method (aka dip coating method) by sonicating the TNA in 0.1M CoCl2 solution for 30 minutes. The sensor response was recorded through electrochemical detection of the four VOBs based on the observable change in current at fixed low bias upon exposure of the sensor to the vapors of the biomarker. In an effort to increase the sensitivity of the sensor, cobalt was incorporated into the titania nanotube lattice through a one step in-situ anodization-co-functionalization process in a CoF2 based ethylene glycol solution. As expected, enhanced sensor response was achieved with reduced time of detection. Further, TNA was functionalized with gold using an electroless deposition technique. Results indicate that sensor response from Au-TNA increased manifold over its Co-TNA counterparts.
The sensor substrates were characterized using SEM, TEM, and XPS. Indirect band gap was calculated based on UV-Vis absorbance. Further, a mechanism has been proposed to describe the attachment of predominate biomarkers to the sensor surface, based on band theory. Overall, the robust synthesis and approach of the sensor demonstrates promise for developing and commercializing a hand-held device for point-of-care diagnosis of pulmonary diseases.