update.337 (fwd)

[Jim Choate <ravage@ssz.com>]

Forwarded message:

> Date: Thu, 18 Sep 97 10:35:28 EDT
> From: physnews@aip.org (AIP listserver)
> Subject: update.337
> 
> 
> PHYSICS NEWS UPDATE                         
> The American Institute of Physics Bulletin of Physics News
> Number 337 September 18, 1997    by Phillip F. Schewe and
> Ben Stein
> 
> REAL PHOTONS CREATE MATTER.  Einstein's equation
> E=mc^2 formulates the idea that matter can be converted into
> light and vice versa.  The vice-versa part, though, hasn't been so
> easy to bring about in the lab. But now physicists at SLAC have
> produced electron-positron pairs from the scattering of two "real"
> photons (as opposed to the "virtual" photons that mediate the
> electromagnetic scattering of charged particles).  To begin, light
> from a terawatt laser is sent into SLAC's highly focused beam of
> 47-GeV electrons.  Some of the laser photons are scattered
> backwards, and in so doing convert into high-energy gamma ray
> photons.  Some of these, in turn, scatter from other laser
> photons, affording the first ever creation of matter from light-on-
> light scattering of real photons in a lab. (D.L. Burke et al.,
> Physical Review Letters, 1 September 1997.)
> 
> DNA-GOLD NANOPARTICLES, employing the talent of DNA
> strands for recognizing and attaching to complementary strands
> and gold's electronic and optical properties, operate as a new
> kind of biosensor.  Scientists at Northwestern University glue
> various "probe" DNA segments onto tiny gold particles (13 nm
> wide).  When a "target" single-stranded DNA  introduced into the
> solution happens to be complementary to DNA already stuck to
> the particles, the probe and target strands link up, creating a sort
> of polymer network whose color is different from that of the
> original solution. Thus recognition of the target DNA is signaled
> by a color change. The researchers can already use this approach
> to detect single-strand DNA samples in 10-femtomolar amounts.  
> (Science, 22 August 1997.)