news
ANALYTICAL CURRENTS Antibody nanoarrays It is hard enough to attach functional biomolecules to a microfabricated surface, but now David Klenerman and colleagues at the University of Cambridge and Imperial College London (both in the U.K.) have gone orders of magnitude smaller and attached antibodies to a nanoscale surface. The approach offers a unique way to create antibody nanoarrays that can address specific features on ultrasmall surfaces. To make the arrays, the researchers fabricated a nanosurface by using a gallium focus ion beam microsope. The surface contained regularly spaced holes within a thin film (50 nm) of gold. The
an electrode in a nanopipette and an ionic solution. The sign and magnitude of the applied voltage were used to control the number of molecules that were delivered. To address each hole individually, the researchers added anti-IgG to the holes containing IgG. They observed green fluorescence from the IgG and red fluorescence from the anti-IgG simultaneously, providing evidence that the antibody–antigen interactions were specific and that a particular feature on a nanosurface can be addressed by adding a second biomolecule. (J. Am. Chem. Soc. 2004, 126, 6508– 6509)
gold film allowed the position of a nanopipette, which was used to deliver biomolecules into the holes, to be viewed by optical microscopy. To resist nonspecific adsorption, the gold surface was coated with a self-assembled monolayer (SAM) that was terminated with hexa(ethylene glycol) groups. The holes were functionalized with a SAM of 3-mercaptopropionic acid, which facilitates the immobilization of IgG antibodies through electrostatic interactions. The researchers delivered IgG antibodies into the holes using a technique in which an ion current flows between
Screening for anthrax inhibitors
(a) 100
Conventional techniques for screening large
to SAMs on a gold-coated
libraries of small compounds use fluorescent
plate. Solutions of anthrax
labels that can interfere with the activities of
lethal factor plus 8 library com-
substrate molecules. High background noise
pounds were spotted onto each
and false positives also can be problems
of the 100 wells on the SAMDI
with fluorescent labeling methods. Milan
plate. When small molecules in
Mrksich and colleagues at the University of
the solution had no effect on
Chicago have abandoned fluorescent labels
the lethal factor, two MS peaks
in favor of MS-based detection. In their ap-
were observed at low m/z val-
proach, self-assembled monolayers (SAMs)
ues, which indicated that the
bound to substrate molecules are adhered
peptide was cleaved. When a
to a MALDI plate, and cleavage of the sub-
small molecule in the spotted
strate is monitored by MALDI TOFMS. The
solution inhibited the cleavage
researchers identified an inhibitor of an-
activity of the lethal factor, two
thrax lethal factor toxin with this SAMs-for-
peaks were observed at high m/z.
MALDI (SAMDI) method.
50 0 1000
2000
3000
4000
Lethal factor
Relative intensity (%)
(b) 100 50 0 1000
2000
3000
4000
m/z
Spectra resulting from (a) inhibition of cleavage and (b) cleavage by anthrax lethal factor. (Adapted with permission. Copyright 2004 Macmillan Publishing Ltd.) centration-dependent manner. The molecule
Using the SAMDI method, Mrksich and
also inhibited cleavage in a solution-based
In the assay, a peptide that can be
colleagues discovered one molecule that
assay and in human cells. (Nat. Biotechnol.
cleaved by anthrax lethal factor is attached
repressed lethal factor cleavage in a con-
2004, 22, 717–723)
© 2004 AMERICAN CHEMICAL SOCIETY
A U G U S T 1 , 2 0 0 4 / A N A LY T I C A L C H E M I S T R Y
255 A
