Digital force-feedback for protein unfolding experiments using atomic force microscopy Bippes, Christian A Harald Janovjak ; https://orcid.org/0000-0002-8023-9315 Kedrov, Alexej Mueller, Daniel J Since its invention in the 1990s single-molecule force spectroscopy has been increasingly applied to study protein (un-)folding, cell adhesion, and ligand–receptor interactions. In most force spectroscopy studies, the cantilever of an atomic force microscope (AFM) is separated from a surface at a constant velocity, thus applying an increasing force to folded bio-molecules or bio-molecular bonds. Recently, Fernandez and co-workers introduced the so-called force-clamp technique. Single proteins were subjected to a defined constant force allowing their life times and life time distributions to be directly measured. Up to now, the force-clamping was performed by analogue PID controllers, which require complex additional hardware and might make it difficult to combine the force-feedback with other modes such as constant velocity. These points may be limiting the applicability and versatility of this technique. Here we present a simple, fast, and all-digital (software-based) PID controller that yields response times of a few milliseconds in combination with a commercial AFM. We demonstrate the performance of our feedback loop by force-clamp unfolding of single Ig27 domains of titin and the membrane proteins bacteriorhodopsin (BR) and the sodium/proton antiporter NhaA. IOP Publishing Ltd. 2007 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/3727 Bippes C, Janovjak HL, Kedrov A, Mueller D. Digital force-feedback for protein unfolding experiments using atomic force microscopy. <i>Nanotechnology</i>. 2007;18(4). doi:<a href="https://doi.org/10.1088/0957-4484/18/4/044022">10.1088/0957-4484/18/4/044022</a> info:eu-repo/semantics/altIdentifier/doi/10.1088/0957-4484/18/4/044022 info:eu-repo/semantics/closedAccess