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

Abstract

A novel AFM technique for single molecule experiments is presented with manipulated micro/nanoparticles.

Nanomechanics on FGF-2 and Heparin Reveal Slip Bond Characteristics with pH Dependency

“…Our customized AFM system, employing an electromagnet with magnetic beads as actuators, has been previously shown to enable force spectroscopic measurements between biotin and streptavidin serving as a well-studied high affinity model receptor ligand system at high loading rates (1 × 10 3 to 3 × 10 3 pN/s). 20 Lowaffinity interactions, characteristic of the FGF-2−heparin complex as reported here, required a stable AFM setup with maximum resolution particularly when used at the low loading rate regime (1 × 10 1 to 1 × 10 2 pN/s). Our setup enabled sensitive biomolecular force measurements as the cantilever is operated away from stationary surfaces, allowing low actuation speeds and decrease of contact forces acting on the interacting biomolecules.…”

“…19 Miniaturized magnetic, PEGylated (to reduce non-specific interactions) microparticles were used as secondary actuator for biomolecular force spectroscopy and force clamp experiments, as schematically represented in Figure 1B. We covalently immobilized low molecular weight heparin onto amine functionalized particles by NHS/EDC chemistry, whereas FGF-2 was physioadsorped onto the cantilever.…”

“…Our magnetic bead actuation methodology (Figure 1B) was used for force clamp experiments as previously described. 20 We deployed various clamping forces, ranging from 19.6 pN to 172.7 pN to study lifetimes between FGF-2 and heparin. A representative force clamp curve for 67 pN clamping force is shown in Figure 3A, resulting in an overall lifetime of 400 ms of the FGF-2 and heparin complex.…”

“…We previously reported on a modular AFM design combining magnetic actuators for single-molecule force measurements. 19 We integrated an electromagnet to a custom-built AFM head to enable direct magnetic actuation of cantilevers for better system dynamics. Furthermore, we employed this system to mechanically actuate functionalized micro/nano-particles against stationary cantilevers in a new mode of operation.…”

Miniaturized magnetic bead-actuators for force-clamp spectroscopy-based single-molecule measurements

“…Previously, we introduced a new method of actuation using magnetic beads as miniaturized actuators for single-molecule experiments without a need for a piezoelectric actuator or a substrate [19] [20]. We use the piezoelectric actuator only for precise positioning and turn it off during data recording.…”