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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.

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

Fibroblast growth factor 2 (FGF-2) -an important paracrine growth factor -binds electrostatically with low micro-molar affinity to heparan sulphates present on extracellular matrix proteins. A single molecular analysis served as a basis to decipher the nanomechanical mechanism of the interaction between FGF-2 and the heparan sulphate surrogate -heparin -with a modular atomic force microscope (AFM) design combining magnetic actuators with force measurements at the low force regime (10 1 -10 4 pN/s). Unbinding events between FGF-2-heparin complexes were specific and short-lived. Binding between FGF-2 and heparin had strong slip bond characteristics as demonstrated by a decrease of life-time with tensile force on the complex. Unbinding forces between FGF-2 and heparin were further detailed at different pH as relevant for (patho-) physiological conditions. An acidic pH environment (5.5) modulated FGF-2 -heparin binding as demonstrated by enhanced rupture forces needed to release FGF-2 from heparin-FGF-2 complex as compared to physiological conditions. This study provides a mechanistic and hypothesis driven model on how molecular forces may impact FGF-2 release and storage during tissue remodeling and repair.3

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