Imaging of magnetic structures and nanoparticles with sub-50 nm spatial resolution in air is usually accomplished with a magnetic force microscope (MFM). However, for a variety of reasons (more details can be found in the report) magnetic nanoparticles below 10–12 nm in size have not been resolved by detecting the magnetostatic interaction. Thus, the spatial resolution to image magnetic interactions in air or liquid is about 10–15 times worse than the spatial resolution to image mechanical interactions under the same conditions.

Resonant coupling

Researchers at the Consejo Superior de Investigaciones Cientificas (CSIC) have developed a novel atomic force method called bimodal force microscopy to simultaneously detect short and long-range forces of different nature. The method is applied to image protein-based magnetic particle carriers in air and liquid with a 5 nm spatial resolution.

The CSIC team has discovered a new nanomechanical process based on the coupling of two resonances of the force microscope microcantilever to identify and separate short- and long-range interactions. The coupling is mediated by the nonlinear character of the tip-surface forces. The technique enables the detection of a minimum magnetic moment around 50 µB in a ferritin molecule with an estimated size of 5 nm. It reaches a lateral magnetic resolution below 7 nm in liquid.

The team presented its work in the journal Nanotechnology.