The brightnesses of fluorescent tags are critical design parameters. In this effort, absolute brightnesses of samples of fluorescent- dye-containing micro- spheres and variations of relative brightness among individual microspheres were measured.

• Optimization of velocity of the molecular shuttles for pick-up of fluorescent tags in the second chamber.

The need for optimization of velocity of molecular shuttles was demonstrated in experiments on the attachment of nanospheres via biotin-streptavidin linkages. The optimum speed depends on the characteristic times of subprocesses involved in the formation of the linkages. In essence, biotin and streptavidin act as glue that must harden for a sufficient time before stress can be applied.

• Proof-of-principle demonstration of a basic biomolecular- motor-powered sensor.

A circular well structure was fabricated by use of a photoresist. Biotinylated microtubules and biotinylated fluorescent microspheres were deposited in a central region of the circular well, leaving a region at the perimeter that was initially free of fluorescent micro-spheres. Injection of streptavidin (as a model of analyte molecules) and subsequent photolytic release of caged adenosine triphosphate led to capture of streptavidin by microtubules, pick-up of microspheres, and, finally, immobilization of microsphere-carrying microtubules at the wall of the well. This shows that molecular shuttles can drive the analyte-dependent transport of fluorescent tags.

This work was done by Henry Hess of the University of Florida for the Air Force Research Laboratory.

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