"The butterfly wing is extremely delicate and fragile, so measuring its mechanical and electromechanical properties by conventional techniques is virtually impossible," Sergei Kalinin of Oak Ridge National Laboratory told nanotechweb.org. "SPM provides the tool that can study these properties even in soft materials."

Kalinin and colleagues Alexei Gruverman and Brian Rodriguez of North Carolina State looked at the wings of the American Lady butterfly (Vanessa virginiensis). They modified a commercial microscope to carry out their atomic force acoustic microscopy measurements.

"To our surprise, we found that acoustic imaging allows us to image much finer details of the internal structure of the biological system than we believed possible," said Kalinin. "The topographic image clearly shows the mesh structure, which enables high mechanical stability and rigidity of the wing. However, no details smaller than around 100 nm can be seen."

Acoustic imaging, on the other hand, revealed details of around 5 nm. The researchers say this is on the length scale of individual chitin fibrils forming the wing.

"In a sense, now we can study mechanical properties on the level of single structural elements forming the biological tissues, eg chitin rods in insects, hydroxyapatite crystals in teeth and bones," said Kalinin. "This will allow us to visualize and understand the effects of diseases such as caries or osteoporosis on hard tissues, and formulate optimal strategies for drug and physical therapies."

Kalinin reckons that mechanical and electromechanical measurements on the cellular level could also provide new strategies for differentiating normal and cancer cells and investigating drug effects.

The researchers would like to make their measurements quantitative, so that they can "say not only whether a particular region is softer or harder, but exactly how hard or soft it is".

They'd also like to achieve higher resolution. "It is great to be able to probe elasticity on the 10 nm scale," said Kalinin, "but can we probe elasticity on the 1 nm or atomic scale? In other words, can we probe a single molecule inside the biological systems or a single unit cell in perovskite?"

Now the team is looking at SPM for probing electrical and electromechanical interactions in biological tissues. "This approach can be expected to provide novel insight into phenomena such as bone growth and remodelling, and muscular activities," said Kalinin. "Currently, we are exploiting the SPM approach to address problems such as cell development or protein imaging."