long as there is monomer available to it. The
researchers first sonicated 5-µm-long PFS/
PDMS micelle cylinders, fracturing them
into 20-nm nanocrystallites. They then used
the crystallites to make micelles from 200
nm up to 2 µm in length by varying the PFS/
PDMS-to-crystallite ratio, achieving nearly
perfectly uniform lengths.—SR
Wax and a dye in layers of a
multilayered device can be
used to time assays.
NEW ROUTE TO GERM-
KILLING PHOTONS
tated by the amount of added paraffin. As
the fluid passes through the paper, it carries
the dye with it. The arrival of the dye at the
end of the channel indicates that the predetermined time has elapsed and the assay
is complete. “We can control the flow rate
from one minute all the way up to two hours
and anywhere in between,” Phillips said.
In time-dependent glucose assays, devices
with integrated timers yielded more precise
and more accurate measurements than did
devices that required external timers.—CHA
odically and some irregularly;
some lit up for longer and
some for shorter periods of
time. Cohen and colleagues
are now trying to pin down
the source and purpose of the
bacterial voltage fluctuations. They are also
working to express the protein in eukary-
otic cells for neuron imaging.—JK
A Georgia Tech team presented new nanomaterials that convert visible light into
ultraviolet radiation. Because the compounds emit UV photons that can damage
microbes’ DNA, engineers Jaehong Kim and
Ezra Cates hope that coating surfaces with
these materials could help disinfect drinking water, sterilize hospital equipment, and
keep bathrooms clean. The nanomaterials
perform their visible-to-UV transformation by a phenomenon called upconversion
photoluminescence, which starts when a
photon of blue light enters the material and
excites an electron from a lanthanide atom.
If that excited state lives long enough, a second blue photon promotes the electron further. When the electron relaxes back to the
ground state, it releases a single high-ener-gy photon of UV light. Upconversion readily occurs in lanthanides because their filled
outer s and p orbitals shield the f orbitals
that contain the photon-excited electrons,
allowing for longer-lived excited states. But
the new nanomaterials work only with specific lanthanides, such as praseodymium,
Cates said, because upconversion requires
electronic states separated by the energy of
a blue photon.—JNC
NEW CLOAK MAY
SUIT MANY DRUGS
BACTERIA CREATE
ELECTRICAL SPIKES
BUILT-IN TIMERS FOR
PAPER DEVICES
Scott T. Phillips and coworkers at Pennsyl-
vania State University described integrated
timers for paper-based microfluidic devices
that allow more precise measurement of
time-based assays than is possible with
external timers such as stopwatches.
Paper-based microfluidic devices are be-
ing developed as inexpensive options for
biomedical assays in resource-limited set-
tings. To avoid the need for external tim-
ers, Phillips built into each device a timer
consisting of paraffin wax and a signaling
dye. The wax slows the movement of fluid
through the paper to a length of time dic-
Bacteria exhibit spontaneous electrical
spiking behavior that may be similar to neu-
ron firing, reported Harvard University’s
Adam E. Cohen. Cohen and colleagues
were working with proteorhodopsin, a
protein that turns sunlight into energy in
some microbes by moving a proton from
one side of the cell membrane to the other.
Ion transport across membranes creates a
membrane potential, or a difference in volt-
age between the outside and inside of a cell.
The researchers were trying to engineer the
protein to essentially run in reverse, chang-
ing its fluorescence emission in response
to a voltage change in a cell, as a means
for imaging electrical activity in neurons.
When they initially expressed the mutated
protein in Escherichia coli, they observed the
proteins flashing on and off “a little bit like
fireflies,” Cohen said. Some flashed peri-
A new type of temporary molecular mask
could help drugs in pill form reach their
destinations more efficiently, according
to researchers at Bristol-Myers Squibb.
The cloaked molecules, called amminium
salts, arise from attaching an amine to a
nitrogen atom on a heterocyclic ring. The
researchers hit upon the idea while trying
to improve an experimental HIV treatment
called BMS-248, which barely reached the
bloodstream when taken orally. The am-
minium version of the drug initially was
an unexpected product from an amination
reaction intended to make BMS-248 more
polar. Inspired by established prodrugs
with N–O bonds, BMS chemists decided to
try using the amminium salt, which features
an N–N bond, as a prodrug—a medication
that is administered in an inactive form that
gets activated in the body. Sure enough,
the compound delivered useful amounts
of BMS-248 to the bloodstream of rats and
dogs. Bacteria in the gut cleave the salt’s
N–N bond to reveal BMS-248. “In principle,
any compound with a nitrogen-containing
heterocycle can be aminated, and the am-
minium salt, providing that it is chemically
stable, could be used as a potential prod-
rug,” said Alicia Regueiro-Ren of BMS.—CD
O
O
F
O
F
N
O
N
N
N
N
N
Gut bacteria
N
HN
+N
NH2
N
Cl–
O
N
H
O
N
Amminium prodrug
BMS-248
