VOC detection: hope or hype? a preliminary study to overcome many challenges

Volatile organic compounds (VOCs) are usually small-size by products of cellular metabolic activity, spreading through bodily fluids (such as breath), that can be regarded as pathophysiological biomarkers. A promising method for developing VOC sensors involves gold nanoparticles (AuNP) to create a lock-and-key system. The concentration of the target molecules interacting with the AuNP detectors can determine a change of electrical resistance and allow VOC concentration to be traced. In this paper, we present our preliminary results on ethanol detection, considered as a model molecule for VOCs, through AuNP synthesis and deposition on cotton, as a flexible and biodegradable substrate. An aqueous gold solution was prepared by using chloroauric acid as gold precursor and polyvinylpyrrolidone as reducing/dispersing agent. The cotton substrate was dip-coated in the solution. The optical characterization in the UV-vis range of both solution and coated cotton revealed the presence of around 20 nm diameter particles associated to a peak at 550 nm. The sample electrical characterization showed different behavior before and after spraying a 40% ethanol solution. In particular, the presence of ethanol brought to an average resistance variation of about 5 orders of magnitude in the 1Hz-1MHz range. Resistance change is probably due to the specific adsorption of the ethanol molecules and the gold nanoparticles/cotton interface. This behavior can be also observed at very low EtOH concentration (up to 1% v/v), showing a promising sensor sensibility. Because of the high capability of AuNP to interact with a wide range of biologically relevant molecules and specifically with the C-OOH or C-OH groups of the VOCs, these pilot results are promising for future applications concerning VOC detection.