Abstract
We report a modular atomic force microscope (AFM) design for biomolecular experiments. The AFM head uses readily available components and incorporates deflection-based optics and a piezotube-based cantilever actuator. Jetted-polymers have been used in the mechanical assembly, which allows rapid manufacturing. In addition, a FeCo-tipped electromagnet provides high-force cantilever actuation with vertical magnetic fields up to 0.55 T. Magnetic field calibration has been performed with a micro-hall sensor, which corresponds well with results from finite element magnetostatics simulations. An integrated force resolution of 1.82 and 2.98 pN, in air and in DI water, respectively was achieved in 1 kHz bandwidth with commercially available cantilevers made of Silicon Nitride. The controller and user interface are implemented on modular hardware to ensure scalability. The AFM can be operated in different modes, such as molecular pulling or force-clamp, by actuating the cantilever with the available actuators. The electromagnetic and piezoelectric actuation capabilities have been demonstrated in unbinding experiments of the biotin-streptavidin complex.
Highlights
Atomic force microscopy (AFM) is best known for high-resolution imaging, but it is a powerful tool for sensitive force measurements
We adopted a modular approach to the design and development of the atomic force microscope (AFM) for biomolecular force spectroscopy applications
It is possible to apply a field of 0.55 T on the cantilever using the electromagnetic actuation capability of the system
Summary
Atomic force microscopy (AFM) is best known for high-resolution imaging, but it is a powerful tool for sensitive force measurements. The resonant frequencies of the large mechanical assembly of the actuator and the holder are usually smaller than the resonant frequency of the cantilever This sets a practical limitation for actuation at high speeds. The cantilever can be actuated using a conventional piezotube actuator or by a FeCo core-based electromagnet integrated to the head The latter requires a magnetic microcantilever for high-force magnetic actuation capability. Coils without cores are usually used to increase bandwidth at the expense of displacement range[20,21] Excessive heating imposes another limitation for the utilization of magnetic actuators, which can provide large displacement range at high bandwidth. This may become especially important for current-carrying cantilevers that experience Joule heating[22,23]. We implemented a software-based controller capable of controlling both actuators for force spectroscopy experiments
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