We developed a molecular sorter that operates without external power or control by integrating the microtubule-based, biological motor kinesin into a microfluidic channel network to sort, transport, and concentrate molecules. In our devices, functionalized microtubules that capture analyte molecules are steered along kinesin-coated microchannel tracks toward a collector structure, concentrated, and trapped. Using fluorescent analyte molecules and nanoliter sample volumes, we demonstrated 14 fM sensitivity, even in the presence of high concentrations of other proteins.
The direction of translocation of microtubules on a surface coated with kinesin is usually random. Here we demonstrate and quantify the rate at which externally applied electric fields can direct moving microtubules parallel to the field by deflecting their leading end toward the anode. Effects of electric field strength, kinesin surface density, and microtubule translocation speed on the rate of redirection of microtubules were analyzed statistically. Furthermore, we demonstrated that microtubules can be steered in any desired direction via manipulation of externally applied E-fields.
Current MEMS and microfluidic designs require external power sources and actuators, which principally limit such technology. To overcome these limitations, we have developed a number of microfluidic systems into which we can seamlessly integrate a biomolecular motor, kinesin, that transports microtubules by extracting chemical energy from its aqueous working environment. Here we establish that our microfabricated structures, the self-assembly of the bio-derived transducer, and guided, unidirectional transport of microtubules are ideally suited to create engineered arrays for efficiently powering nano- and microscale devices.
We suggest a concept for powering microfluidic devices with biomolecular motors and microtubules to meet the demands for highly efficient microfluidic devices. However, to successfully implement such devices, we require methods for active control over the direction of microtubule translocation. While most previous work has employed largely microfabricated passive mechanical patterns designed to guide the direction of microtubules, in this paper we demonstrate that hydrodynamic shear flow can be used to align microtubules translocating on a kinesin-coated surface in a direction parallel to the fluid flow. Our evidence supports the hypothesis that the mechanism of microtubule redirection is simply that drag force induced by viscous shear bends the leading end of a microtubule, which may be cantilevered beyond its kinesin supports. This cantilevered end deflects towards the flow direction, until it is subsequently bound to additional kinesins; as translocation continues, the process repeats until the microtubule is largely aligned with the flow, to a limit determined by random fluctuations created by thermal energy. We present statistics on the rate of microtubule alignment versus various strengths of shear flow as well as concentrations of kinesin, and also investigate the effects of shear flow on the motility.
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