Surface Imaging

The self-propelled movement of microtubules with a diameter of 30 nm on a kinesin-coated surface provides us with a novel nanoscale probe, which can explore a surface in a radically different fashion compared to the tip of a scanning probe microscope. While scanning probe microscopes use a single tip, which scans the surface in a controlled, linear movement, the microtubule movement per se is random. Therefore it is necessary to synthesize an image of the surface based on the random paths of a large number of microtubules exploring the unknown surface at the same time. A basic implementation of this new approach to surface imaging (Fig. 5) was demonstrated for a surface with a structured topography,[56] but the research into guiding mechanisms for nanoscale transport systems indicates that the microtubule path is influenced by surface chemistry or fluid flow as well. Despite its limitations due to the sensitivity of the proteins and the optical detection of the microtubule position, the described technique is an example of how the availability of self-propelled nanoprobes enables the implementation of a new scanning method with similarities to mathematical Monte Carlo methods. Nanotechnology is

Fig. 5 Fluorescently labeled microtubules transported by surface-adsorbed kinesins can serve as nanoscale probes exploring the surface. The sensitivity of the microtubule path to the topography allows us to image an unknown surface.[56] This is illustrated in (A), where a microfabricated pattern of 1-mm-high posts divides the surface into an accessible and an inaccessible region, because microtubules move on the bottom surface and are unable to climb a steep incline. Repeated observation of microtubule positions under the fluorescence microscope as shown in (B) yields information about the path of several hundred microtubules. The superposition of 500 images taken every 5 sec reveals the surface topography (C). Source: From Ref.[56]. © 2002 Am. Chem. Soc.

Fig. 5 Fluorescently labeled microtubules transported by surface-adsorbed kinesins can serve as nanoscale probes exploring the surface. The sensitivity of the microtubule path to the topography allows us to image an unknown surface.[56] This is illustrated in (A), where a microfabricated pattern of 1-mm-high posts divides the surface into an accessible and an inaccessible region, because microtubules move on the bottom surface and are unable to climb a steep incline. Repeated observation of microtubule positions under the fluorescence microscope as shown in (B) yields information about the path of several hundred microtubules. The superposition of 500 images taken every 5 sec reveals the surface topography (C). Source: From Ref.[56]. © 2002 Am. Chem. Soc.

not always "the same but smaller.'' Instead, sometimes "small is different'' (Uzi Landman) applies, which creates opportunities to utilize nanosystems for innovative technologies.

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