PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 704 October 13, 2004
by Phillip F. Schewe, Ben Stein

A REALISTIC LASER-OPERATED MOLECULAR LOCOMOTIVE has been proposed by a
Texas A&M researcher (Zhisong Wang, nargate{at}jewel.tamu.edu). For those
designing materials at the smallest workable scales, a major dream is to
build nano-locomotives that would move through a molecular-scale track to
perform various tasks, such as transporting building blocks for
nanomachines.  Earlier proposals have outlined some innovative designs for
these nanoengines (for example, see
http://www.aip.org/pnu/2000/split/pnu490-1.htm).  While nano-locomotives
are still in the blueprint stage, a new model brings the idea closer to
reality by incorporating the latest working knowledge of nanomaterials as
well as the probabilistic, jiggly nature of the molecular world.  In Wang's
design, a nano-locomotive would have a main body consisting of cars each
made up of a linear polymer chain.  Either end of the train would have a
chemically tailored "head" group that could bind to or break from
a track, which could be a cylinder-shaped microtubule found in biology. 
Either end of the locomotive could attach via covalent bonds to special
molecular groups on the track.  Laser pulses would move the train: one
light pulse would break the bond from one of the train's ends and another
laser pulse would cause each car of the train to change its molecular
configuration, and expand its size to reach the next part of the track. 
Thermal fluctuations of the motor itself and the environment play a vital
role, for example as the train's head seeks the next binding site on the
track.  Wang has proposed a multistep "optomechanical work cycle"
that precisely outlines the laser steps needed to move the train, and even
reverse its direction.  The locomotive would work not only as a motor, but
a powerful molecular engine that could generate a pulling force 10 times
greater than of the natural biomotor kinesin.  Such forces, of about 100
piconewton, could allow the nano-locomotive to break molecular bonds and
help in constructing nanomaterials while delivering ca
rgo. (Wang, Physical Review E, 15 September 2004; also see
http://focus.aps.org/story/v13/st27).

FINDING A VEIN, necessary for administering intravenous solutions, can
often be difficult.  A new device, called a Vein Contrast Enhancer (VCE),
uses sensitive infrared sensing to find the vein beneath the skin and then
also projects the rather spooky vein image back onto the patient's wrist. 
This makes it appear as if the veins were lying right on top, making it
easy for a nurse to make an injection. How does it work?  An array of light
emitting diodes shines infrared light at the subject, and one depends on
the fact that red blood cells scatter light differently from surrounding
fatty tissue.  The scattered light passes through some filters and then is
captured by a CCD TV camera, processed by computer, and rendered as a sort
of movie at a rate of 30 frames per second. These images can be projected
onto the subject through a careful aligning process to register the surface
projection with subcutaneous anatomy (see figure at www.aip.org/png). 
Herbert Zeman and his colleagues at the University of Tennessee Health
Science Center in Memphis have done extensive clinical trials with VCE
devices and are now doing trials with the projection capability. The
general spatial resolution of the process is about 0.1 mm.  Veins as deep
as 8 mm have been imaged.  This work is being presented at this week's
Frontiers in Optics meeting in Rochester, co-sponsored by the Optical
Society of America (OSA) and the American Physical Society (APS).
(http://www.osa.org/meetings/annual/. See also http://www.conenhill.com/)

---