Research

POROUS MATERIALS SUBGROUP

In this subgroup, we design, synthesize, characterize, and modify metal-organic frameworks (MOFs) and porous organic polymers (POPs) for catalysis, kinetic diffusion studies, and other applications.

MOFs are a class of porous and crystalline coordination polymer that comprises inorganic metal nodes and organic linkers. We utilize these MOFs as support platforms for catalysts to access homogeneously inaccessible species that are then capable of catalytic conversions in the solution and the gas-phase.  We are also interested in fine-tuning the biocompatibility of MOFs for catalysis and sensing under bio-relevant conditions.  We have also tailored these MOFs to remove toxic aqueous moieties.

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POPs are porous materials constructed from organic monomers linked by covalent bonds.  In addition to the incorporation of catalytically active moieties into POPs, we have also engineered larger pores into microporous POPs by carrying out the polymerization inside a mesoporous silica aerogel template.  The broad range of pore sizes allows for much faster transport of molecules, resulting in increased diffusion rates, faster uptake, and faster capture/catalytic activities compared to MOF and POPs with only micropores.

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GRAPHENE/GRAPHENE OXIDE GROUP

In this subgroup, we focus on extending the excellent nanoscale mechanical properties of graphene and graphene oxide (GO) to their macroscale composites.  While graphene and GO have superior mechanical properties at the nanoscale, the mechanical properties of their macroscopic composites are orders of magnitude lower, limiting their structural applications.  Thus, we are developing bottom-up design principles that can overcome these limitations through the multi-length scale bridging of mechanical properties.  In collaboration with the Espinosa group, we are fabricating GO composites with well-defined nanoscale compositions and structures to explore the effect of interfacial interactions and functional group distribution on mechanical properties over several length scales.3

BIOMATERIALS SUBGROUP

This subgroup focuses on utilizing biomolecules to construct nanoscale vehicles for therapeutic and self-assembly applications.  This is accomplished through several approaches in collaboration with the Mirkin, O’Halloran, and Schatz groups.

We have made acid-degradable polymer-caged lipoplex (PCL) platform by combining a cationic lipoplex core and a biocompatible, pH-responsive polymer shell. These PCLs serve as effective delivery vehicles of small interfering RNA through a combination of facile loading, rapid acid-triggered release, enhanced cellular internalization, and endosomal escape.

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We made liposomal spherical nucleic acid (LSNA) by combining 30 nm liposomal cores with a dense shell of oligonucleotides functionalized with a hydrophobic tail that can intercalate into the liposome structure.  The resulting LSNA rapidly enters multiple cell lines without the need for ancillary transfection agents and can be used to effectively knockdown gene expression via antisense pathways.

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Small molecule-DNA Hybrids (SMDHs) comprise oligonucleotides covalently linked to organic molecules in well-defined numbers and geometrical positions.  We have used SMDHs as multifunctional programmable building blocks for forming higher order structures composed of purely organic material or interfaced with other DNA-coated systems such as nanoparticles.

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