Highly vertical 3D bio-inspired hierarchical and multiscale superstructures on microcantilever for gas sensing of organophosphorous agents

Abstract

Microgravimetric sensors offer promising solution to detect volatile compounds. However, they suffer from a low surface-to-volume ratio limiting the maximum amount of adsorbate that can be fixed on their 2D surface. In this study, we report a bio-inspired method to elaborate highly vertical 3D hierarchical and multiscale superstructures in order to greatly increase the surface area of the microcantilever and to capture more molecules in vapor phase. However, building such superstructures on the microcantilever surface remains challenging in terms of structural design and synthesis while preserving a sufficient response of the sensor at low gas concentration. These particular superstructures are inspired from the antenna of the silkmoth Bombyx mori which is composed of a stem with branches on either side, themselves covered with sensilla. A patterned-microcantilever with high-aspect-ratio silicon micropillars is therefore used as support to generate a dense array of titanium dioxide nanorods decorated by goethite nanobranches. 3D hierarchical superstructures show a high enhancement in the response of the sensor to vapor of dimethyl methylphosphonate, a common simulant of sarin considered as one of the most toxic molecules. This design generates mass and surface stress effects under exposure to low vapor concentrations allowing to reach a limit of detection of 3 ppb. The sensor shows also a fast response to a wide range of concentrations. These results provide promising prospects to improve the detection potential of microcantilever-based sensors by using complex superstructures and dedicated materials to generate stress effect on the microcantilever surface and overcome the conventional microcantilever sensors based only on mass variation.