www.sciencemag.org SCIENCE VOL 303 16 JANUARY 2004 287

A P P L I E D  P H Y S I C S

Transistors Turn On
the Light

The field of optoelectronics
usually requires the integration
of separate devices with optical
and electronic functionalities.
The extra masking, patterning,
and wiring processes involved in
the integration add significantly
to the fabrication time and
therefore to the cost of the end
product. Furthermore, as these
“separates” need to talk to each
other, there may also be a re-
duction in the device perform-
ance. Feng et al. have fabricated
a heterojunction bipolar transis-
tor based on an InGaP/GaAs
structure that combines both
functions—three-terminal elec-
tronic control and optical func-
tion—in one device. They
demonstrate that as their tran-
sistor is turned on, it also emits
light as the injected carriers re-
combine in the vicinity of the
base layer contact. By modulat-
ing the current of the base layer
contact, they also demonstrate

the ability to switch the light
emission at rates up to 1 MHz.
Although this modulation rate
is rather slow, but perfectly suf-
ficient for display purposes,
present wide-bandgap hetero-
junction transistors can now
achieve switching rates of 450
GHz, indicating a possible use
for these light-emitting transis-
tors in optical communication
networks. — ISO

Appl. Phys. Lett. 84, 151 (2004).

M I C R O B I O L O G Y

Vaccinating Cattle

Contaminated food—hamburg-
ers are a notorious exam-
ple—is the primary source
of dangerous enteric infec-
tions by Escherichia coli
O157:H7 (EHEC), which in
humans can cause bloody
diarrhea and, in some cas-
es, hemolytic uremic syn-
drome. Because EHEC has
been found in almost 50%
of beef carcasses in North
America, an important
commercial aim is to re-

duce exposure to the bacteria
by reducing the extent to
which EHEC colonizes the 
cattle intestine.

EHEC virulence is attributed
to the ability to secrete deter-
minants, via a type III secretion
system, that include the ad-
hesins Tir and EspA and the
pore-forming protein EspB,
which together promote bacte-
rial attachment to host cells.
Potter et al. have chosen these
molecules as constituents of a
trial vaccine for calves. The trial
was carried out under commer-
cial livestock-rearing conditions,
and the trial animals were then

exposed to the O157:H7 strain.
Vaccination increased specific
antibody titer 45-fold after a
single booster and reduced the
duration and quantity of EHEC
shedding. As well as being eco-
nomical to prepare, a livestock
vaccine must be effective
enough to minimize the num-
ber of times an animal has to
be handled, which would add
to rearing cost. Plus, developing
a livestock vaccine might be a
useful route to a human vac-
cine against EHEC. — CA

Vaccine 22, 362 (2004).

C H E M I S T R Y

Super Switcher

The extent to which water can
wet a surface is dependent on a
number of factors, including the
chemistry and the roughness of
the surface. Various methods
have been used to change the
extent of wetting dynamically,
but they cover only a limited
range of water contact angles.
Sun et al. show that they can
reversibly switch a surface from
being superhydrophilic to being
superhydrophobic with a very
small change in temperature.
On its own, poly(N-isopropy-
lacrylamide) will switch from
being hydrophilic to being mild-
ly hydrophobic when the tem-
perature is raised from 25° to
40°C. At the lower tempera-
tures, the C=O and N-H groups
are partnered by water mole-
cules, and intermolecular hydro-
gen bonding dominates; when
the temperature is raised, in-
tramolecular hydrogen bonding
takes over, ejecting the water

molecules, and the chains
adopt a more compact form.
The authors enhanced this
transition by depositing the
polymer onto patterned sili-
con substrates. As the pat-
tern size was decreased (fin-
er grooves), they observed
an increase in the range of
contact angles achieved on
switching. Detailed investi-

EDITORS’ CHOICE

C L I M A T E  S C I E N C E

Testing the Waters

Iron fertilization of the surface
ocean layer has been considered
as a possible strategy for reduc-
ing the burden of atmospheric
CO2; this would mitigate green-
house gas buildup and global
warming. The idea is that CO2
would be removed from the at-
mosphere by sequestering it as
new ocean production in “high
nutrient—low chlorophyll” re-
gions, where biological produc-
tion is limited by the scarcity of
iron. This approach might have

other consequences, however, including the increased production and atmospheric concentration
of N2O, another powerful greenhouse gas.

Using a suite of three-dimensional, coupled physical-biogeochemical models and an oceanic N2O
cycle module, Jin and Gruber assess how excess production caused by iron fertilization would affect
atmospheric N2O. They find that additional N2O production could offset 100% of the effect of CO2
removal when fertilization of limited duration and size is undertaken in the tropics, and that small-
er but still substantial offsets can be expected when fertilization is undertaken elsewhere over
longer periods. These results indicate that ocean fertilization with iron, in order to reduce atmos-
pheric CO2, may be less efficacious than has been hoped. — HJS

Geophys. Res. Lett. 30, 10.1029/2003GL018458 (2003).

H I G H L I G H T S O F T H E R E C E N T L I T E R A T U R E

edited by Gilbert Chin

Fe

Diatom

Foraminifera

CO2

N2O

Fe Fe

Compensatory greenhouse gas fluxes.

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CONTINUED ON PAGE 289

EHEC adhering to human

intestinal cells.

EHEC adhering to human

intestinal cells.

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gation of the substrate showed a large frac-
tion of irregular nanoparticles produced by
sputtering from neighboring regions and
thus a very large surface area. — MSL

Angew. Chem. Int. Ed. 43, 357 (2004).

B I O P H Y S I C S

Small is Beautiful

Although many biologists
are interested in phenome-
na operating on micro-
meter-to-nanometer scales,
they often rely on their
physical science colleagues
in adapting existing technology to new us-

es: for example, x-
ray crystallography
for structure deter-
mination of
macromolecules
and atomic force
microscopy for
probing single bio-
molecules.
Alivisatos reviews

the recent crossover of quantum dots—
clusters of roughly a few thousand inor-
ganic atoms with favorable properties for
biological imaging (intense stable fluores-
cence in the visible region). Lidke et al.

illustrate their
use with
epidermal
growth fac-
tor—quantum
dot (EGF-QD)
conjugates.
EGF binds to
members of
the erbB family

of receptor tyrosine kinases, and inappro-
priate expression of these receptors is im-
plicated in some types of cancer.
Fortunately, EGF-QDs also bind to these
receptors, making it feasible to monitor
endocytosis and intracellular trafficking of
the growth factor. Coupling the use of
these ligands to expression of various fluo-
rescent pairs of erbB receptors suggested
that heterodimerization of erbB1 and B2
(but not erbB1 and
B3) is triggered by
the interaction
with EGF. — GJC 
Nature Biotechnol. 22, 47;
10.1038/nbt929 (2004).

G E O C H E M I S T R Y

Selenospheres

Selenium is an important biological trace
element: an essential part of some metallo-

enzymes and a nutrient at low
concentrations, but a pollutant
and a toxic species at high lev-
els. Elemental selenium is used
in many electronics applica-
tions, and recent efforts have
focused on growing microscopic
selenium wires and crystals
with advantageous characteris-
tics and optical properties for

use in devices. Oremland et al. show that
phylogenetically distinct groups of bacteria
that live in a range of environments process
selenium in ways that may bear on these
aspects of selenium chemistry. These bacte-
ria reduce selenium oxyanions in order to
grow and deposit elemental selenium exter-
nally. Imaging and spectroscopy show that
the selenium is precipitated as uniform
crystalline nanospheres about 300 nm in
diameter. Surprisingly, different bacteria
produce spheres with different arrange-
ments of the selenium atoms and hence
different optical properties. — BH

Appl. Environ. Microbiol. 70, 52 (2004).

B I O M E D I C I N E

The LO Road to Atherosclerosis

Lipoxygenases (LOs) are a family of en-
zymes that are attracting attention be-
cause of their role in the biosynthesis of
lipids that mediate inflammatory and aller-
gic reactions. Inhibitors of these enzymes
are already in clinical use for treatment of
asthma. Because lipid-mediated inflamma-
tory circuits are also etiologic factors in
atherosclerosis, Dwyer et al. investigated
whether genetically determined variation
in LOs might contribute to vascular dis-
ease. In a pilot study of 470 healthy indi-
viduals, they found that two variant alleles
of the gene encoding 5-LO were associated
with an increase in carotid artery intima-
media thickness, an established indicator of
systemic atherosclerosis. Notably, the ef-

fects of these variant alleles appeared to
be modified by dietary intake of certain
types of fatty acids, such as those in ma-
rine fish. This study and a recent mouse
analysis linking a different LO gene to os-
teoporosis (see Reports, 9 January 2004,
p. 229) broaden the scope of disorders
that are potentially treatable with drugs
targeting these enzymes. — PAK

N. Engl. J. Med. 350, 29 (2004).

www.sciencemag.org SCIENCE VOL 303 16 JANUARY 2004

CONTINUED FROM 287   EDITORS’ CHOICE

Retrograde transport

of EGF-QDs (red) in a

filopodium (green).

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Small is Beautiful
Gilbert J. Chin

DOI: 10.1126/science.303.5656.289a
 (5656), 289.303Science 

ARTICLE TOOLS http://science.sciencemag.org/content/303/5656/289.1

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© 2004 American Association for the Advancement of Science

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