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Search This Site | People | Departments | Penn State
Mark A. Snyder
Department of Chemical Engineering and Materials Science
University of Minnesota
Thursday, April 24, 2008
102 Chemistry Building
10:00 a.m. - 11:00 a.m.
The ability to synthesize size-tunable (5-25 nm), monodisperse, and stable inorganic nanoparticles under benign conditions, and to assemble them into nanoparticle-crystals and ordered particulate films has technological implications spanning catalytic (i.e., single site acid catalysts), coatings and separations (i.e., chemical sensors, colloidal lithography, porous films), and biological (i.e., high-resolution bioimaging, immune protection). While silica nanoparticles are attractive for such applications, achieving these properties has remained elusive with common synthesis techniques (e.g., Stöber, precursor zeolite nanoparticles, reverse micelles). Drawing motivation from ubiquitous silica structures arising from neutral conditions in nature, we have identified the formation of stable silica nanoparticles as small as 4 nm in diameter in basic amino acid-silica sols.
The novelty of the synthesis derives from its simplicity and benign nature (i.e., more neutral pH), where hydrolysis of a silica source is accomplished in an aqueous solution of L-Lysine. Despite its simplicity, this technique yields particles bearing a remarkably narrow size distribution and a wide range of handles for tuning particle size from smaller than 5 nm to larger than 20 nm. Successful assembly of the nanoparticles into nanoparticle-crystals and ordered multi- and monolayer coatings has implications for thin film applications, where micro and mesoporosity, imparted by the interstitial spacing, can be engineered by fine control of particle size.
Exciting applications in the biological arena also become more feasible as a result of the benign nature of the lysine-silica synthesis. In particular, we have shown that further neutralization of the lysine-silica sols by addition of compatible peptide oligomers (e.g., di-lysine) can lead to the formation of clear, porous silica gels. We have employed the resulting porous gels for living cell encapsulation as proof-of-concept work towards realizing implantable devices capable of simultaneously trafficking metabolites of interest while minimizing immunological rejection.