Dually actuated atomic force microscope with miniaturized magnetic bead-actuators for single-molecule force measurements

We report a novel atomic force microscopy (AFM) technique with dual actuation capabilities using both piezo and magnetic bead actuation for advanced single-molecule force spectroscopy experiments. The experiments are performed by manipulating magnetic microbeads using an electromagnet against a stationary cantilever. Magnetic actuation has been demonstrated before to actuate cantilevers, but here we keep the cantilever stationary and accomplish actuation via free-manipulated microstructures. The developed method benefits from significant reduction of drift, since the experiments are performed without a substrate contact and the measured force is inherently differential. In addition, shrinking the size of the actuator can minimize hydrodynamic forces affecting the cantilever. The new method reported herein allows for the application of constant force to perform force-clamp experiments without any active feedback, profiled for a deeper understanding of biomolecular interactions.