How to engineer superhydrophobic micromechanical sensors preserving mass resolution

Micro- and nano-mechanical resonators such as cantilevers and pillars are more and more used as molecular sensors, due to their high sensitivity, ease of fabrication and high throughput. In order to modify their wetting properties and to prepare them for the selective adsorption of the molecules of interest, the sensor active surface has to be properly functionalized. This can significantly affect their mechanical performances. In this paper we report on the effect on a micropillar array of different hydrophobic treatments, based on plasma deposition of a fluorocarbon film (FCF) and on the formation of an alkanosilane coating, to obtain a superhydrophobic state. Each treatment was characterized by measuring the change of the quality factor in vacuum, the static contact angle and evaluating the compatibility with gold deposition, to create a bio-functional layer. As case study, DNA self assembled monolayer (SAM) formation and hybridization efficiency were measured. Finally, the superhydrophobicity was tested with diluted human plasma, as preliminary step toward the use of micropillars for biomolecular detection in human samples.