Protein-Directed Self-Assembly of Gold Nanoparticles
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Protein-Directed Self-Assembly of Gold Nanoparticles Alexey A. Vertegel,1,2 Wen Shang,2 Jonathan S. Dordick2,4, and Richard W. Siegel2,3 1 Now at: Department of Bioengineering, Clemson University, Clemson SC 29634 2 Rensselaer Nanotechnology Center and Departments of 3Materials Science and Engineering and 4 Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 ABSTRACT We have employed protein-protein interactions for controlled assembly of gold nanoparticles. Stoichiometric 1:1 protein:nanoparticle conjugates were prepared for proteins known to strongly interact with each other and these interactions were used to self-assemble nanoparticles. Mixing equivalent amounts of the antigen-nanoparticle and antibody-nanoparticle conjugates resulted in the formation of nanoparticle dimers with a yield of about 60%. Trimers (yield ~30%) can be obtained by mixing 2:1 antigen-nanoparticle with 1:1 antibody-nanoparticle conjugates in a molar ratio of 1:2. The structures are destroyed at low pH when the antibody-antigen complex dissociates. INTRODUCTION Many proteins and peptides are known to form self-assembled structures. Use of proteindirected self-assembly provides exciting opportunities to create tailor-made nanostructures due to the diversity of existing forms (e.g., wires, rings, and catenans) and the possibility to control the assembly/disassembly process in situ as a result of the sensitivity of protein-protein interactions to minor changes in solution pH, Ca2+ concentration, presence of an inhibitor, etc. Proteindirected self-assembly has been used for years as a functional component of immunoassays [1]. Recently, the highly specific streptavidin-biotin interaction has been used to assemble 8 nm Au nanoparticles [2] and 5 nm ferric oxide nanoparticles [3]. Niemeyer [4] reported the formation of di-, tri-, and tetramers of biotinylated 1.4 nm Au nanoparticles (Nanogold) upon interaction with streptavidin-DNA conjugates. However, in none of these cases was the exact stoichiometry of nanoparticle aggregates controllable. Alivisatos [5,6] successfully prepared Nanogold-quantum dot assemblies with defined stoichiometry and geometry (Nanomolecules) using interactions between complimentary DNA strands. The formation of designed structures in this case was achieved by controlling the number of DNA strands attached to a single nanoparticle. We expanded this approach by using stoichiometric protein-nanoparticle conjugates and employed strong antigen-antibody interactions to achieve the nanoassembly of 5 nm gold nanoparticles. We also show that the resulting nanostructures can be controllably disassembled at low pH, which destroys protein-protein interactions within the nanoassembly. EXPERIMENTAL DETAILS FITC-labeled and unlabeled rabbit polyclonal immunoglobulin G (IgG, anti-horseradish peroxidase antibody) was purchased from Jackson ImmunoResearch, Inc. FITC-labeled and unlabeled polyclonal Fab’ fragment of anti-rabbit IgG (anti-IgG) was purchased from Protos Immunoresearch. All ot
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