Nanoparticle Engineering

Colloids functionalized with self-assembled monolayers (SAMs) are inherently nanoscopic entities that provide a both a scaffold for receptor creation and a building block for microscale constructs. We are currently pursuing both of these avenues, targeting issues in both biological chemistry and materials science.

In one research program, we are exploring the use of colloidal particles as solution-based receptors. In preliminary studies, we have demonstrated efficient redox-controlled molecular recognition of flavin by functionalized gold nanoparticles. This control of flavin recognition provides an effective model for flavoenzyme processes, while also providing a method for extending molecular devices to larger constructs. In further studies, we fabricated nanoparticles featuring a combination of hydrogen bonding and aromatic stacking recognition elements. These nanoparticle receptors were environmentally responsive: incubation of the receptors with target molecule increased the efficiency of the recognition process.

Templation of colloid-based receptor by a multivalent guest. From:"Fabrication and Self-Optimization of Multivalent Receptors on Nanoparticle Scaffolds" A. Boal, V. Rotello, J. Am. Chem. Soc., 2000, 122, 734-735.

This templation provides a powerful tool for the creation of systems capable of selective recognition of complex biomolecules. We are currently developing nanoparticles designed to bind to protein surfaces and cell surface receptors; these systems could serve both diagnostic and therapeutic roles in biomedical applications. As a first step, we have developed water-soluble amphiphilic colloids. These colloids provide the starting point for our biomolecular recognition research.

TEM micrographs of w-thiol carboxylic acid functionalized colloid at (a) pH 10, (b) pH 7, and (c) pH 4. Scale bar represents 10 nm, 25 nm, and 50 nm, respectively. From : J. Simard, C. Briggs, A. Boal, V. Rotello, J. Chem. Soc., Chem. Comm. in press.

In another ongoing project, we are using electrostatic interactions to provide controlled assembly of nanoparticle systems. Using this methodology, we have created a variety of microscale systems, ranging in structure from rounded to fractal.

Fractal-like nanoparticle arrays formed via self assembly of gold and silica nanoparticles. From: A 'Building Block' Approach to Mixed-Colloid Systems through Electrostatic Self-Organization" T. Galow, A. Boal, V. Rotello, Adv. Materials, 2000, 12, 576-579.

By combining our polymer and nanoparticle self-assembly strategies, we have developed a general means for the controlled self-assembly of nanoparticles. In this "bricks and mortar" strategy, colloidal gold particles functionalized with recognition elements serve as the bricks, while polymers bearing complementary functionality serve as mortar, holding together the colloidal particles. Using this strategy, the conformational flexibility of the polymer compensates for irregularities in the size and shape of the aggregate structure, allowing the efficient propagation of order during the self-assembly process. With this methodology, we assembled 2 nm cold particles into highly ordered spherical clusters 97 nm ± 17 nm in diameter.

a) Polymer mediated self-assembly of Thy-Au. b) TEM micrograph of Thy-Au-polymer 1 aggregate. From: "Self-Assembly of Nanoparticles into Giant Spherical Arrays" A. Boal, F. Ilhan, J. DeRouchey, T. Thurn-Albrecht, T. Russell, V. Rotello, Nature,2000, 404, 746.

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Group publications in nanoparticle engineering

"Intra- and Inter-Monolayer Hydrogen Bonding in Amide Functionalized Alkanethiol SAMs on Gold Nanoparticles" A. Boal, V. Rotello, Langmuir., submitted for publication.

"Formation and pH-Controlled assembly of Amphiphilic Gold Nanoparticles" J. Simard, C. Briggs, A. Boal, V. Rotello, J. Chem. Soc., Chem. Comm. in press.

"Polymer-Mediated 'Bricks and Mortar' Self-Assembly of Nanoparticles into Discrete Structured Arrays" Polymer Preprints, 2000, 1348-1349.

"A 'Building Block' Approach to Mixed-Colloid Systems through Electrostatic Self-Organization" T. Galow, A. Boal, V. Rotello, Adv. Materials, 2000, 12, 576-579.

"Fabrication and Self-Optimization of Multivalent Receptors on Nanoparticle Scaffolds" A. Boal, V. Rotello, J. Am. Chem. Soc., 2000, 122, 734-735.

"Divergent Surface Functionalization Using Acid Fluoride-Functionalized Self-Assembled Monolayers" A. Niemz, E. Jeoung, A. Boal, R. Deans, V. Rotello Langmuir, 2000, 16, 1460-1462.

"Self-Assembly of Nanoparticles into Giant Spherical Arrays" A. Boal, F. Ilhan, J. DeRouchey, T. Thurn-Albrecht, T. Russell, V. Rotello, Nature, 2000, 404, 746-749.

"Redox-Modulated Recognition of Flavin by Functionalized Gold Nanoparticles" A. Boal, V. Rotello, J. Am. Chem. Soc., 1999, 121, 4914-4915.