Comparing membrane- and cantilever-based surface stress sensors for reproducibility
Point-of-care (PoC) applications require small, fast, and low power sensors with high reliability. Despite showing promising performances, nanomechanical sensors have not yet demonstrated the excellent reproducibility of measurements necessary to be incorporated-in such systems. Coffee-ring effect usually occurs during the deposition of the functionalization layer and produces an inhomogeneous and poorly repeatable profile on the sensor surface. In this study, we investigated how cantilever-based sensors and the previously developed membrane-type surface stress sensor (MSS) are affected by an inhomogeneous functionalization. We functionalized 8 piezoresistive cantilevers and 16 MSS with a dextran solution that formed an inhomogeneous layer due to the coffee ring effect. During expositions to humidity pulses, MSS was five times more reproducible (standard deviations between 5% and 6%) compared to the cantilever-based sensors (standard deviations between 25% and 28%). In fact, the cantilever-based sensors were as reproducible as their functionalization layer while the reproducibility of MSS was only limited by the tolerances of their fabrication. This sensor-to-sensor reproducibility, combined with a high sensitivity, makes the MSS a promising bio/chemical sensor platform for reliable and label-free detection of substances to be integrated into PoC systems. (C) 2015 Elsevier B.V. All rights reserved.