  Microtubules are filament-shaped, polymeric proteins (~25 nm in diameter)
involved in cellular structure and organization. We demonstrate the imaging of
individual microtubules using a conventional bright-field microscope, without
any additional phase or polarization optics. Light scattered by microtubules is
discriminated through extensive use of digital image-processing, thus removing
background, reducing noise and enhancing contrast. The setup builds on a
commercial microscope, with the inclusion of a minimal and inexpensive set of
components, suitable for implementation in the student laboratory. We show how
this technique can be applied to a demonstrative biophysical assay, by tracking
the motions of microtubules driven by the motor protein kinesin.
