| Abstract
| - We report herein biotin−streptavidin-mediated aggregation studies of long gold nanorods. We havepreviously demonstrated end-to-end linkages of gold nanorods driven by the biotin−streptavidin interaction(Caswell et al. J. Am. Chem. Soc. 2003, 125, 13914). In that report, the specific binding of biotin disulfideto the gold nanorod edges was achieved due to the preferred binding of thiol molecules to the Au{111}surface (gold nanorod ends) as opposed to the gold nanorod side faces. This led to the end−end linkageof gold nanorods upon subsequent addition of streptavidin. In this report we demonstrate a simple procedureto biotinylate the entire gold nanorod surface and subsequently form a 3-D assembly by addition ofstreptavidin. Gold nanorods were synthesized by the three-step seeding protocol documented in our previousarticles. The surface of gold nanorods was further modified by a layer of a weak polyelectrolyte, poly(acrylicacid), PAA. A biotin molecule which has an amine group at one end (biotin−PEO−amine) was anchoredto the carboxylic acid group of the polyelectrolyte using the well-known carbodiimide chemistry. Thisprocess biotinylates the entire gold nanorod surface. Addition of streptavidin further leads to aggregationof gold nanorods. A closer look at the aggregates reveals a preferential side-to-side assembly of gold nanorods.The gold nanorods were characterized at each stage by UV−vis spectroscopy, light scattering, andtransmission electron microscopy (TEM) measurements.
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