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Atomic Force Microscopy Using Insulated Conductive Cantilevers
Recently, electrically conductive cantilevers for atomic force microscopy have been developed
and characterized in a NCCR Nanosciences collaboration between the universities of Basel and
Neuchâtel [1-3]. The cantilevers are constructed using standard microfabrication techniques
that allow batch fabrication [1]. Using these techniques an insulation layer covering the
main conductive parts of the cantilevers was implemented without impairing the mechanical
properties compared to non-conductive cantilevers. To obtain conduction, the insulation of the
cantilever is removed over ~100 nm from the metal tip-apex. The result is a cantilever of
"standard" dimensions in combination with a conically shaped ultramicroelectrode (UME) of ~100nm
base radius and height and with a sharp metal tip (radius < 20 nm).
For current sensing an in-house designed current-to-voltage converter was developed that is
capable of measuring currents with pA resolution at a bandwidth of ~2 kHz [2]. These
cantilevers open an avenue of new applications in electrochemistry and biology. For
electrochemistry, feedback and scanning electrochemical experiments aim to measure the
relationship between topographical and electrochemical properties of (electrode) surfaces.
The small size of the UME allows the study of heterogeneous electron transfer rates up to
~10-2 m/s. At the same time, the small UME size enables measurements of differences in rate
constants with spatial resolutions of less than 10 nm [2, 3]. In biology, the same
electrochemical techniques can be applied to measure structure-function relationships of
biological molecules that are embedded in lipid bilayer membranes, like detecting open/closed
protein conformations or electron transfer through redox proteins.
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Front cover of Nanotechnology (August 2005). In front: SEM micrograph of an insulated
conductive cantilever, with a fine metal tip sticking out of the pyramidal tip [1]. On
the background data are shown that were recorded with such a conductive cantilever: In
the bottom a patch of Hexagonally packed intermediate (HPI) layer of Deinococcus
radiodurans adsorbed on a highly oriented pyrolytic graphite support is shown. In the
top correlation averages are shown of the HPI surface structure (left) and simultaneously
recorded faradaic current (right) [2]. |
[1] |
Development of Insulated Conductive Probes with Platinum Silicide Tips for Atomic Force Microscopy in Cell Biology
Terunobu Akiyama, Maurizio R. Gullo, Nicolaas F. de Rooij, Andreas Tonin, Hans-Rudolf Hidber, Patrick L. T. M. Frederix, Andreas Engel and Urs Staufer
Japanese Journal of Applied Physics 43, 3865-3867 (2004)
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[2] |
Assessment of insulated conductive cantilevers for biology and electrochemistry
Patrick L T M Frederix, Maurizio R Gullo, Terunobu Akiyama, Andreas Tonin, Nicolaas F de Rooij, Urs Staufer and Andreas Engel
Nanotechnology 16 (2005): 997-1005
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[3] |
Characterization of batch fabricated probes for combined atomic force and
high-resolution scanning electrochemical microscopy
Gullo M. R., Frederix P. L. T. M., Akiyama T., Engel A., de Rooij N. F., and Staufer U.
in preparation
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Contact:
Patrick Frederix |
Andreas Engel |
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M.E. Müller Institute for Structural Biology
Biozentrum, University of Basel
Switzerland |
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