Fabrication and Characterization of Micromachined Active Probes With Polymer Membranes for Biomolecular Force Spectroscopy

A micromachined polymer membrane-based active probe has been developed for biomolecular force spectroscopy. The probe has integrated but significantly decoupled electrostatic actuation and optical interferometric force sensing capabilities. Devices have been fabricated on silicon substrates using Parylene as the membrane material. The electrostatic actuator integrated into the probe could provide > 1-μm displacement with a flat response of up to 30 kHz in fluid, a feature particularly useful in fast-pulling force spectroscopy experiments involving biomolecules. The probes were successfully employed to measure the unbinding forces between biotin and streptavidin, wherein the force noise level was <;10 pN with a 1-kHz bandwidth for an 8-N/m membrane with a 25-kHz resonance frequency in fluid. This is in agreement with the thermal noise data generated by a finite-element model that predicts further improvements with simple design changes.