An additive manufacturing concept, consisting of 3D photopolymer printing and Ag nanoparticle printing, was investigated for the construction of a microfluidic biosensor based on immobilized cytochrome P450 enzyme. An acylate-type microfluidic chamber composed of two parts, i.e. chamber-housing and chamber-lid was printed with a polyjet 3D printer. A 3-electrode sensor structure was inkjet-printed on the lid using a combination of Ag and graphene printing. The working electrode was covered with carbon nanotubes by drop-casting and immobilized with cytochrome P450 2D6 enzyme. The microfluidic sensor shows a significant response to a test xenobiotic, i.e. dextromethorphan; the cyclic voltammetrical measurements show a corresponding oxidation peak at 0.4 V with around 5 μM detection limit.
Two types of MOx sensor structures, SnO<sub>2</sub> and WO<sub>3</sub>, of different thicknesses were synthesized on top of the interdigitated Au electrodes and used for the measurements of the ethylene gas. The SEM micrographs revealed inhomogeneities of the WO<sub>3</sub> layer and the presence of cracks on the edges of Au electrodes which correlates with the lack of reproducibility of the WO<sub>3</sub> sensors. Both sensor structures showed a significant sensitivity to ethylene gas: the sensitivities of both MOx-types were higher at higher temperatures which was more evident in the case of SnO<sub>2</sub> structure. The SnO<sub>2</sub> layer had approximately 5-times higher sensitivity than the WO<sub>3</sub> sensor of the same thickness. The saturation (T10) and desaturation (T90) times were shorter for WO<sub>3</sub> sensors at lower temperatures while SnO<sub>2</sub> was saturated and desaturated faster at higher temperatures. Sensors with thinner active layer possessed higher sensitivities and shorter T10 and T90 times.