A micromachined membrane-based active probe for biomolecular mechanics measurement

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A novel micromachined, membrane-based probe has been developed and fabricated asassays to enable parallel measurements. Each probe in the array can be individuallyactuated, and the membrane displacement can be measured with high resolution using anintegrated diffraction-based optical interferometer. To illustrate its application insingle-molecule mechanics experiments, this membrane probe was used to measureunbinding forces between L-selectin reconstituted in a polymer-cushioned lipid bilayer onthe probe membrane and an antibody adsorbed on an atomic force microscope cantilever.Piconewton range forces between single pairs of interacting molecules were measured fromthe cantilever bending while using the membrane probe as an actuator. The integrateddiffraction-based optical interferometer of the probe was demonstrated to have<10 fm Hz−1/2 noise floor for frequencies as low as 3 Hz with a differential readout scheme. With soft probemembranes, this low noise level would be suitable for direct force measurements withoutthe need for a cantilever. Furthermore, the probe membranes were shown to have0.5 µm actuation range with a flat response up to 100 kHz, enabling measurements at fast speeds.