Gold-imidazole nanoparticles detected in vivo
Gold nanoparticles are being developed for molecular detection, biological
imaging and targeted drug delivery. It is desirable to combine them with imidazole
because it is the reactive moiety of many biological molecules, according to J.
Houston Miller and others at George Washington University in Washington and at the University of Texas M.D. Anderson Cancer Center in Houston. The researchers
say that such nanoparticles can increase data acquisition speeds and reduce laser
power required for in vivo detection. To prove it, they used near-IR surface-enhanced
Raman spectroscopy to detect gold-imidazole nanoparticles in vitro and in vivo.
Imidazole, in the center, interacts with two surrounding gold nanoparticles. Researchers showed
that imidazole catalyzes gold nanoparticle assembly by direct participation. In
the future, gold-imidazole nanoparticles may be used as biological probes. Reprinted
with permission from J. Houston Miller. Copyright 2006 American Chemical Society.
They mixed imidazole and gold nanoparticle solutions,
and the gold-imidazole particles assembled themselves by adsorption. Because biological
tissue absorbs little near-IR radiation, and the surface-enhanced Raman spectroscopy
signal from imidazole exhibits a dramatic peak wavelength upon near-IR excitation,
they examined the imidazole solution with near-IR Raman spectroscopy, but the signal
was weak. Surface-enhanced Raman spectroscopy boosted the imidazole signal by a
factor of 2 x 106.
Above 1.9 μM, imidazole catalyzed gold nanoparticle
aggregation. Nanoparticles with fewer aggregates have a high surface area, which
improves their binding efficiency and accessibility to binding sites, resulting
in a larger spectroscopic signal. Thus, lower concentrations of imidazole can be
used when making gold-imidazole nanoparticles for use as biological probes.
The investigators injected 300 μl
of gold-imidazole nanoparticles into tumors in mice and collected the light 3 mm
above the skin using a 7-mm-focal-length fiber optic probe to perform surface-enhanced
Raman spectroscopy. Only the mice that were injected with the nanoparticles exhibited
the imidazole peak. The researchers said that the apparatus was not designed for
in vivo detection, but that it provided proof-of-principle.
Besides establishing that this technique
can be used in vivo, they eventually want to systemically deliver targeted nanoparticles
using technology such as phage display vectors.
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