Gold nanoparticles have shown great promise in a variety of biological
applications including the use in highly sensitive diagnostic assays 1,2,
thermal ablation 3, radiotherapy enhancement 4, as well as drug and gene
delivery 5. Such gold particles, however, suffer from losing or reducing
sensitivity and selectivity due to aggregation under high ion strength of
biological fluids and non-specific interaction with biomolecules, such as
proteins or DNA. Poly ethylene glycol (PEG), which is known to lengthen
the circulation time of biomedicines in the bloodstream, reducing the
non-specific binding of proteins, and increasing efficacy and
tolerability, is currently used as coating for different kind of
nanoparticles to improve their stability and biocompatibility. The
currently used strategy was to attach PEG moelcucles to gold nanoparticle
through Au-SH chemical bonding. There is no available information,
however, about how the length, conformation and attachment sites of PEG
moiety affect the binding stability on gold nanoparticles, which play
such critical role in retaining the solubility, while facilitating both
selectivity and reactivity. In our present work we examined the stability
of thiolated PEG with different length and multi-thiol anchors bound to
gold nanoparticle by an assay of PEG displacement with different moities
including di-thiolthreitol (DTT) and mercaptoethanol. Dynamic light
scattering (DLS), Atomic force microscopy (AFM), multiangle-laser light
scattering (MALS) incorporated with refractive index (RI), UV and DLS
detectors were employed to characterize size, geometry, and packing
density of PEG. This information will enable us to understand, optimize
and control their efficacy and distribution of gold nanoparticle-based
diagnostic or therapeutic agents under complex physiological
environments. 1 Tkachenko, A.G.; Xie, H.; Coleman, D.; Glomm, W.; Ryan,
J.; Anderson, M.F.; Franzen, S.; Feldheim, D.L. J.Am. Chem.
Soc.2003,125,4700.2 Nam, J.M.; Thxton, C.S.; Mirkin, C.A.; Science 2003,
301, 1884.3 Loo, C.; Lowery, A.; Halas, N.; West, J.; Drezek, R. Nano.
Lett. 2005, 5, 709.4 Hainfeld, J.F.; Slatkin, D.N.; Smilowitz, H.M.;
Phys. Med. Biol. 2004, 49, N309.5 Thomas, M.; Klibanov, A.; Proc. Natl.
Acad. Sci. USA 2003, 100, 9138.