“This is the first time that an image of better than 10 nm resolution has been generated using the Faraday current,” Andreas Engel of the University of Basel told nanotechweb.org. “In addition, we have found quite unexpectedly that the image quality changes drastically in normal-contact-mode AFM when a voltage is applied to the metal tip.”

Engel and colleagues used a cantilever with a platinum, iridium or platinum silicide core. A layer of insulating silicon nitride fully enclosed the core, apart from at the apex of the cantilever tip.

The team found that applying a voltage between the tip and the sample support improved the contrast of the image. The tip was also able to measure variations in diffusion-limited faradaic current over objects less than 5 nm across.

“The applications we have in mind are related to biology,” said Engel. “However, these tips will find many interesting applications in electrochemistry, in the study of material corrosion, and perhaps even in testing electronic circuitry.”

The researchers claim their conductive cantilever had tip dimensions and mechanical properties comparable to those of commercial non-conductive cantilevers used for contact-mode imaging of biological samples.

“On the technical side, we now have to make the tips more reliable, integrate them in a device that makes handling easier and hopefully find a partner that will produce them commercially,” said Engel.

The scientists also plan to use the conductive tips to study the dynamics of membrane proteins. Applying an electric field to the membranes should induce membrane channels to open or close.

“To apply these cantilevers to membrane channels, we have to purify such proteins and reconstitute them in lipid bilayers,” said Engel. “This is indeed a big challenge and we will have to invest a major effort in the endeavour.”

The researchers reported their work in Nanotechnology journal.