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ANALYTICAL CURRENTS Micropatterned live-cell bioassay
Viruses bring order to quantum dots A team of scientists believes their ap-
ent, self-supporting film. The ~15-µm-thick
proach to ordering quantum dots may
film was ordered at the nano- and microm-
provide new pathways to organize elec-
eter scales into 72-µm domains, which
tronic, optical, and magnetic materials.
repeated continuously over several cen-
Angela Belcher and colleagues at the
timeters. The liquid crystalline phase be-
University of Texas–Austin use a liquid
havior of the hybrid material could be
crystal system to fabricate highly ordered,
controlled by varying the solvent concen-
self-supporting films from genetically en-
tration or by using an applied magnetic
gineered M13 bacteriophage and ZnS
field.
nanocrystals.
FN
BSA
The researchers say that the phages,
M13—chosen because the virus natu-
which are essentially monodisperse
rally has monodisperse size and shape—
biopolymers of specified length, can be
was altered to express a peptide that rec-
easily prepared by molecular cloning
ognizes ZnS crystals. The modified phages
techniques. In addition, it should be easy
were added to ZnS precursor solutions,
to modulate and align different types of
where they physically bound ZnS crystals
inorganic nanocrystals, such as CdS, PbS,
and, as the solvent was gradually re-
and CdSe, in 3-D layered structures. (Sci-
moved, spontaneously formed a transpar-
ence 2002, 296, 892–895)
Phage library with 109 random peptide inserts Bioselectivity
ZnS
Figure not available for use on the Web.pH Repeat interaction
Nanocrystal binding
elution
Bacterial amplification
Liquid crystal alignment Schematic diagram of the process used to generate nanocrystal alignment by the phage display method. (Adapted with permission. Copyright 2002 American Association for the Advancement of Science.) 360 A
A new in vivo assay on live cells monitors respiration to measure changes in cell physiology. Matsuhiko Nishizawa, Kimiyasu Takoh, and Tomokazu Matsue of Tohoku University (Japan) micropattern mammalian HeLa cells on a glass substrate and study the oxygen concen-
A N A LY T I C A L C H E M I S T R Y / J U LY 1 , 2 0 0 2
50 µm Optical microscope image showing the selective attachment of HeLa cells to the fibronectincoated region, rather than the bovine serum albumin region, of a glass plate.
tration by scanning electrochemical microscopy (SECM). The researchers take advantage of the adhesion-promoting and -inhibiting properties of fibronectin (FN) and bovine serum albumin (BSA), respectively, to construct their biosenor on a hydrophobic, insulating glass plate. FN and BSA do not require the glass substrate to be precoated with a metal, as do some systems, and thus eliminate possible interference with the SECM signal. An FN pattern is imprinted on a glass plate using a poly(dimethylsiloxane) stamp. The plate is then rinsed and incubated in BSA solution to cover the rest of the surface. Incubation in a HeLa suspension for an hour allows cells to attach to FN, and subsequent incubation in a cell-free medium allows cell spreading. SECM and optical microscope images
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show HeLa cells in island and band patterns. A SECM platinum microelectrode scanning 10-µm high determines that spreading cells in band patterns consume larger amounts of oxygen than round cells in island patterns. Because respira-
tosis. Nishizawa and his colleagues propose that spreading cells in the band pattern consume more oxygen than round cells in the island pattern because they are still growing. (Langmuir 2002, 18, 3645–3649)
tion directly correlates with cellular status, the FN–BSA-patterned plate is a valuable tool for bioassays. Previous work by others has shown that cell shape is related to many cell functions, including cell death by apop-
Visible computing with glow discharge Think there’s nothing new in microchips for solving computational problems? Andreas Manz, Darwin Reyes, and colleagues at Imperial College (U.K.) and Harvard University might make you think again. The microfluidic chips created by these researchers can solve various maze-search and shortestpath problems, such as finding the shortest route between two landmarks. Although the shortest path can be readily found with an algorithm, the complexity of the problem, and thus the time required to find a solution, increases with the number of decision points along the way. So, the researchers abandoned algorithms and adopted the more literal approach of representing the problem as a series of channels etched into a microfluidic chip. They used electrodes to mark the starting and ending destinations and generated an on-chip glow discharge, which lit up the shortest route. After verifying the approach on some simple problems, they demonstrated the system’s practical use by Trafalgar Square
finding the shortest route between Imperial College and London landmarks, such as Trafalgar Square. The method was fast, plotting a course through 456 decision points (2456 possible pathways) in
