100
percent
PGA Tour pro’s
chance of sinking
a one-foot putt
50
percent
PGA Tour pro’s
chance of sinking
a 7.8-foot putt
5
percent
PGA Tour pro’s
chance of sinking
a 38-foot putt
Engineered cells alive and lasing
Coherent light generated with green fluorescent protein
By Devin Powell
The first living laser is nothing to be afraid
of. It’s just a single cell pulsing with light
that may lead to new ways of probing
microscopic realms.
The secret to the cell’s splendor is
called green fluorescent protein, or
GFP, researchers report online June 12
in Nature Photonics.
First discovered in jellyfish, this glowing protein has long helped biologists
illuminate cells and their inner workings.
When struck by blue light, its electrons
essentially jump up and down and fluoresce with green light.
The green light emitted by one GFP
molecule can also trigger another GFP
molecule to spit out identical green light.
Two physicists have now used this phenomenon, called “stimulated emission,”
to set off the chain reactions required to
make laser light from GFP.
“They’ve shown that you can do lasing
action in a live cell without destroying the
cell,” says physicist Stefan Hell of the Max
Planck Institute for Biophysical Chemistry in Göttingen, Germany.
In their first experiment, Seok-Hyun
Yun and Malte Gather of Massachusetts
General Hospital and Harvard Medical
School placed two mirrors close together
and filled the space in between with liquid
containing GFP. Brief pulses of blue light
excited the proteins, which set each other
off with help from the mirrors and created
pulses of green laser light more intense
than the original blue light.
The principle is similar to that of dye
lasers, which also amplify light using dissolved organic molecules — not proteins,
but compounds such as coumarin dyes,
derived from substances in grasses that
smell like freshly mowed hay.
Then the physicists pimped their
GFP laser by replacing the free-floating
molecules with a single mammalian cell
containing a bit of DNA that churns out
a mutant form of the fluorescent protein.
When stimulated, the cell could pulse
with light a few hundred times before
the GFP gave out (technically, photo-
bleached).
A genetically engineered cell creates
laser light (green) using green fluores-
cent protein, discovered in a jellyfish.
distribution of the proteins within a cell
should change the characteristics of the
emerging laser light.
Yun and colleagues are also replacing
the mirrors with reflective nanostruc-tures inside cells. Such cells might be able
to lase from within biological tissue.
Better putting
with geometry
Physicist golfer offers advice
on getting ball into the hole
By Devin Powell
A Yale physicist with a lifelong passion
for golf has figured out a better way to
putt on a slope. Thanks to the geometry of
the game, he says, there’s a magic spot just
uphill of a hole. The trick is to line up the
putt not only from where the ball lies, but
also from equidistant points nearby. Do
that and the sweet spot will reveal itself.
“Many golfers use a mental image of
pouring a bucket out on the green and
visualize where the water would flow,”
says Mark Broadie, a researcher at the
Graduate School of Business at Columbia
University who has developed a new statistic for measuring putting performance.
Robert Grober, an experimental
physicist at Yale University, imagines the
ball sitting on a circle centered at the hole.
At the 12 o’clock position, the ball travels
directly downhill along a straight line
to find the hole. But a ball hit from, say,
4 o’clock must roll uphill along a curve to
reach the hole. Grober calculated these
curves from different points on a circle,
treating the green as a tilted flat surface
and taking into account the pull of gravity
and the resistance of the grass.
www.sciencenews.org
July 16, 2011 | SCIENCE NEWS | 15
