Room temperature ethanol sensor with sub-ppm detection limit: Improving the optical response by using mesoporous silica foam.

In this paper, the improvement in room temperature ethanol sensing characteristics of zinc peroxide (ZnO 2 ) based hybrid thin films is presented by the combination of the beneficial sensing properties of mesoporous materials and reflectometric interference spectroscopy (RIfS). The hybrid thin films were prepared by Layer-by-Layer (LbL) self-assembly method from ZnO 2 nanoparticles, polyelectrolyte [poly(acrylic acid), PAA] and/or mesoporous silica (MPS). The expected improved sensing properties were attributed to the fractal properties and high specific surface area ( a s ) of the mesoporous coating/interlayer material, which was evidenced by small angle X-ray scattering (SAXS) and N 2 sorption measurements (a s > 650 m 2 /g). The sensor tests showed that the detection limit of the thin films is in the sub-ppm range (<500 ppb). Applying silica foam (SF) as surface coating or interlayer material in the sandwich-structured thin film (ZnO 2 /SF) improved the optical response (Δl: wavelength shift) compared to the ZnO 2 /PAA thin layer, but the sensitivity showed non-linear characteristic and signal drift. The thin film with mixed structure (ZnO 2 /PAA/ZnO 2 /SF) showed linear sensitivity (Δλ/Δc = 0.6 nm/ppm) in the 0.5–12 ppm range with an acceptable selectivity and stable baseline. Testing the sensor in extended (up to 40 ppm) concentration range showed only a slight quadratic deviation from linear behavior with R 2 = 0.9987. [ABSTRACT FROM AUTHOR]