Interferometric readout of multiple cantilever sensors in liquid samples

Abstract

Microcantilever sensors in the static mode are a promising technology for chemical and biological detection in liquid phase. However, despite their potential for arrayed operation, most demonstrations to date have been performed with single devices due to the limitations of current methods for measuring cantilever displacement. We report a new readout technique using a curved semitransparent SU-8 cantilever on a reflective substrate. The displacement is measured by analyzing the interference pattern in microscope images of the device. Multiple cantilevers are read out with a single microscope by translating the stage to image each device before and after a chemical sample is introduced. Since the images are precisely aligned in software, the position of the stage is not critical, and the image acquisition is rapid. As a proof of principle, the cantilever displacement caused by pH variations or binding of homocysteine is measured. The experiments are performed with 3, 5, or 8 parallel devices exposed either to the same solution or to different sample concentrations. The minimal detectable displacement was determined to be on the order of 1 nm. The presented design and readout method can potentially be adapted for applications such as DNA hybridization assays or immunoassays in array format.