Visions of a better microarray
a genomics or proteomics microarray that can be analyzed with surface-enhanced Raman
scattering, a technique that can detect single molecules. What if the array could
be designed to produce a maximally enhanced signal? Christopher J. Addison and
Alexandre G. Brolo at the University of Victoria in British Columbia, Canada, have
determined that surface enhancement is affected by varying the composition of nanoparticles
on a glass slide, an early step toward establishing such a microarray.
In their experiment, the scientists alternately
deposited gold nanoparticles and a dithiol molecule onto glass surfaces and characterized
them with UV-visible spectroscopy, atomic force microscopy and surface-enhanced
Raman scattering. Using a spectrometer from Varian Inc. of Lexington, Mass., they
examined the gold nanoparticle-coated glass slides in air and in water at a resolution
of 2 nm. At a rate of 333 nm/min, they scanned a range of wavelengths from 400 to
900 nm. Then they studied the slides with an atomic force microscope and noncontact
silicon microscope tips, both from Veeco Instruments Inc. Finally, they added oxazine
720 dye to probe the array with a Raman spectrometer from Renishaw.
As reported in the Oct. 10 issue of
Langmuir, the spectra became more redshifted with increasing amounts of nanoparticles,
and atomic force microscopy showed structures that progressively grew with nanoparticle
deposition. Those results suggest that the nanoparticles became more aggregated
with increasing nanoparticle deposition.
For surface-enhanced Raman scattering
measurements at 632 and 785 nm, nine and 13 nanoparticle depositions, respectively,
exhibited a maximally enhanced signal. The signal increased to 100 times that of
a single deposition, but the surface area increased only 20 percent, as measured
by atomic force microscopy.
The researchers concluded that varying
the number of depositions could enable maximum enhancement at various excitation
wavelengths. It also could permit the creation of an array that produces various
wavelengths that represent different cellular information.
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