Graphene-like sensing film inkjet printed on paper for ethanol detection

The detection of volatile organic compounds (VOCs) is an always current topic that widely attracts the scientific community for being crucial in several applications mainly related to environment, health and industrial processes monitoring. Among the VOCs, ethanol is a common organic vapour frequently employed as reference parameter for food quality control, fermentation process or human breath thus resulting in an increasing request of low-cost, eco-compatible ethanol sensors able to work at room temperature. Such objective can be pursued by merging new material sensing properties with eco-sustainable fabrication processes and substrates. In this framework, the inkjet printing (IJP) technology, a deposition method from liquid phase, well addresses this demand for its patterning capability, which permits an efficient use of different functional inks so reducing the amount of waste products, and the employable (nonflexible and flexible) substrates. The latter issue promotes the use of paper as low cost and eco-sustainable substrates. In this perspective, we fabricated an ethanol chemiresistor by IJP an aqueous suspension of graphene-like (GL) layers. The sensing ink was prepared through a two steps oxidation/reduction method starting from a nanostructured carbon black [1,2]. GL layers as other graphene related materials present interesting properties for sensing applications at room temperature: high conductivity and stability, large specific surface areas and tunable performances. The GL layers-based ink was deposited by IJP onto glossy paper where interdigitated Cr/Au electrodes were previously e-beam evaporated. The printing parameters were optimized in order to obtain uniform, conductive and reproducible sensing films. The final sensor device was exposed to 50 ppm of ethanol at RT in dry N2, setting the voltage at 1 V. Differently from pristine graphene that is completely insensitive to ethanol, GL material shows a conductance variation when exposed to this analyte. This sensitivity may be attributable to adsorption or desorption of molecules on the surface of the GL layers film assisted by the presence of residual oxygen functional groups, mainly carboxylic groups, as confirmed by X-ray Photoemission Spectroscopy.