news
Electronic noses strive for diversity Most electronic nose technologies try to mimic, to some degree, the way the human nose detects odors, but it’s no easy task. It has been estimated that humans have ~1000 genes that Hexane DRmax/Rb 3 100
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Methanol
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presumably encode ~1000 olfactory proteins. This collection of proteins is thought to broadly respond to odor molecules and generate a pattern of unique responses that the brain recognizes as a specific aroma. Analytical chemists know how to interpret patterns, but how do you create a sensor with 1000 detectors? Nathan Lewis’s group has joined with Robert 80 100 Grubbs’s group (both at the California Institute of Technology) to find new sensor compounds using a combinatorial approach. They use an electronic nose strategy
developed in Lewis’s group, which relies on arrays of carbon black/polymer composites. The swelling of the polymers leads to an increase in dc resistance in the composite film, generating those human-like recognition patterns. Two strategies are employed to produce new sensing materials. One approach creates a series of block copolymers that vary in their combination of monomers, and the other method systematically modifies the properties of a single polymer by adding a series of plasticizers. Both approaches show promising results. Even better, both could be the basis of a manufacturing strategy that places an array of pixellike detectors on a “nose chip” using a limited number of feedstocks. (J. Comb. Chem. 2000, 2, 301–304)
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Varying combinations of polar and nonpolar monomers yields block copolymers with different responses to gas-phase analytes.
Microscale bead beds One of the main advantages of going to
Sciences (both in Canada) describe an
tein melittin in 5 s, compared with 10–15
the microscale for protein work is the
integrated microfluidic device that uses
min off chip, and the digestion of cyto-
potential for speeding up the analyses.
an immobilized trypsin bead bed for pro-
chrome c in 3–6 min. The researchers
Toward that end, D. Jed Harrison, Can
tein digestion and incorporates CE and
attribute these results to the increased
Wang, and colleagues at the University
an electrospray MS interface.
mass transport and higher bead-to-pep-
of Alberta and the Institute for Biological
a
Protein digestion was performed in a large channel (800-µm
C
capillary tip
F
B
A
E
wide 3 150-µm deep 3 15-
D MS
/~/15 mm Top view
10 µm
150 µm
800 µm
b
230 µm
syringe pump
/~/15 mm Side view
(a) Schematic of the integrated enzyme reaction bed and CE chip. (b) Top and side views of the packed trypsin bead bed. (Adapted with permission. Copyright 2000 John Wiley & Sons, Ltd.)
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A N A LY T I C A L C H E M I S T R Y / O C T O B E R 1 , 2 0 0 0
tide ratio of the packed bed over “inreservoir” digestion methods. The subsequent separation of the
mm long) packed with
peptides was performed in a 30-µm-wide
trypsin-immobilized beads.
3 45-mm-long channel and took 3 min.
Sample was pumped
The amino acid sequence coverage
through this digestion bed
ranged from 92% for cytochrome c to
at 0.5–60 µL/min, and the
71% for bovine serum albumin. (Rapid.
researchers report the di-
Commun. Mass Spectrom. 2000, 14,
gestion of the simple pro-
1377–1383)
