Piconewton regime measurements of biomolecular interactions by nanomechanical force gauge

A piconewton regime measurement of biomolecular interactions in an aqueous solution by a novel nanomechanical force gauge (NFG) is presented in this paper. A highly sensitive nanoscale cantilever with a spring constant, which is thousand times smaller than that of an atomic force microscope (AFM) microcantilever, is fabricated by a batch process. The NFG has a capability of direct reading without any optical amplification. The control of nanoscale thickness of a single crystal silicon cantilever is done by a thermal oxidation process. The deflection of the cantilever, corresponding to piconewtons is directly measured by reading the tick movements in the reading scale of the NFG under the microscope. The spring constant of the NFG is calculated by identifying the natural frequency using electrostatic force excitation, and the minimum value of the designed device was 78.6 pN/μm. As an example of the biomolecular applications, the dissociation between a biotinylated bead and avidins is measured, and the mean is 636 pN. The NFG has the potential of 1 pN/μm sensitivity through the nanofabrication technology as well as serving as an inexpensive and powerful substitute for an atomic force microscope in studying biomolecular interactions.