Making Atomic Force Microscopy Useful for Cellular Imaging

U.S. scientists have developed nanosized cantilevers whose gentle touch could help discern the workings of living cells and other soft materials in their natural, liquid environment. Used in combination with an innovative detection mechanism, this new imaging tool is sensitive enough to investigate soft materials without the limitations present in other cantilevers.

Atomic force microscopy, a tactile-based probe technique, provides a three-dimensional (3D) nanoscale image of a material by gliding a needle-like arm across the material's surface. The core of this AFM imaging technology is a cantilever with a sharp tip that deflects as it encounters undulations across a surface. Due to a minimum force required for imaging, traditional AFM cantilevers can deform or even tear apart living cells and other biologic substances. While scientists have made strides in reducing this minimum force by making smaller cantilevers, the force is still too great to image cells with high resolution. Indeed, for imaging objects smaller than the diffraction limit of light, that is, nanometer dimensions.

"Whether we are considering biological systems or other complex, self-assembling nanostructures, this organization will be done in a liquid,” said Dr. Paul Ashby, a molecular foundry staff scientist who led this research in the Molecular Foundry's Imaging and Manipulation of Nanostructures Facility, a U.S. Department of Energy (DOE) User Facility located at Lawrence Berkeley National Laboratory (Berkeley, CA, USA). "If we have an investigative probe that excels in this environment, we could image individual proteins as they function on the cell surface.”

According to Dr. Babak Sanii, a postdoctoral researcher in the Foundry, "Shrinking the cantilever down to nanoscale dimensions dramatically reduces the force it applies, but to monitor the movements of such a small cantilever, we needed a new detection scheme.”

Instead of measuring the cantilever's deflection by bouncing a laser off it, Dr. Ashby and Dr. Sanii placed the nanowire cantilever in the focus of a laser beam and detected the resulting light pattern, pinpointing the nanowire's position with high resolution. The scientists reported that this research provides a starting point for building a nanowire-based atomic force microscope that could be used to study biologic cells and model cellular components such as vesicles or bilayers. Specifically, they hope to learn more about integrins, proteins found on the surface of cells that mediate adhesion and are part of signaling pathways linked to cell growth and migration.

"No present technique probes the assembly and dynamics of protein complexes in the cell membrane,” added Dr. Ashby. "A dynamic probe is the holy grail of soft matter imaging, and would help determine how protein complexes associate and disassociate."

The research was published in April 2010 in the journal Physical Review Letters.

Related Links:
Lawrence Berkeley National Laboratory's Molecular Foundry