|Benign Synthesis, Size Control, and Assembly of Silica Nanoparticles: A New Paradigm for Dispersed Particle, Porous Thin Film, and Gel Applications |
Chemical and Biochemical Engineering
|Mark A. Snyder, University of Minnesota|
10:20 - 11:40 a.m. – Room 116, BME (note new location)
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). In addition, harsh synthesis conditions (e.g., high pH, alcoholic solutions) preclude their direct use for benign materials synthesis and biological applications. While exquisite silica structures are formed in nature under benign conditions, peptide-mediated biomimetic routes pursued in the laboratory have yielded only polydisperse, unstable silica nanoparticles.
Operating at the interface between these approaches, we have recently 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, where hydrolysis of a silica source (tetraethylorthosilicate) is accomplished in an aqueous solution of L-Lysine. The initial stage of nanoparticle formation mimics that for tetrapropylammonium- (TPA) and other alkylamonium-silica nanoparticles with rapid nanoparticle formation occurring upon exceeding the silica solubility limit. This simple technique yields particles bearing a remarkably narrow size distribution and a wide range of handles for tuning particle size (e.g., sol pH, silica content, synthesis and ageing temperatures) from smaller than 5 nm to larger than 20 nm. Their facile assembly 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. These materials also hold exciting prospects as infiltration templates for fabricating inverse opal films (e.g., carbon) with pore spaces that could be employed for applications spanning separations to sensing to confined materials synthesis.
Exciting applications in the biological arena also become more feasible as a result of the benign nature of the lysine-silica synthesis. As an example application, 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 silica gels with tunable porosity. We have employed this benign gelation for living cell encapsulation, harnessing the tunable gel porosity to facilitate nutrient and metabolite regulation and to promote cell viability. This proof-of-concept work underscores the benign nature of the lysine-silica nanoparticle sols and their gels, and opens possibilities for realizing implantable devices capable of simultaneously trafficking metabolites of interest while minimizing immunological rejection.
(Refreshments served 10:00 a.m.)
For further information call (732) 445-4949 or 2228