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Our general theme is to exploit various forms of self-assembly to achieve nanoscale materials with responsive properties, at the intersection of materials science and biotechnology. We have largely, though not exclusively, focused our attention on biopolymer systems composed of nucleic acids and/or polypeptides, to benefit from tunable interactions with unmatched precision. These and other well-defined macromolecules are the natural choices for studying self-assembly in solution or at interfaces, with obvious implications for sensors and drug/gene delivery.

Solution self-assembly

I. DNA-based assembly is promising approach to circumvent limitations of traditional gene and drug delivery, potentially eliminating the need for polycation condensation. Our efforts have demonstrated the importance of DNA's mechanical properties at the nanoscale [1,2], as well as pioneering the use of DNA nanostructures as therapeutic delivery vehicles [3]. More recently, we have begun to explore the role of kinetics on self-assembly.

II. Viruses and virus-based particles provide opportunities to use recombinant DNA/protein engineering methods to control presentation of reactive groups, to introduce asymmetry, and to incorporate stimulus-responsive motifs at the nanoscale. We have explored the third aspect to endow virus particles with precisely defined functionality [4]. Such levels of control are often difficult, if not impossible, to achieve with more traditional inorganic nanoparticles. Potential applications include biosensors and intracellular probes.

Interfacial self-assembly

I. The engineering of surfaces that are capable of controlling cell adhesion has been widely explored, and is largely limited to patterning strategies. In nearly all of these works, such systems are inherently static. By contrast, the cellular micro-environment is dynamic and is remodeled by biochemical reactions and biophysical forces. We have borrowed this concept from Nature to create self-assembled polymeric films that exhibit lateral (i.e., in-plane) diffusive motion [1]. Cells placed on these films are sensitive to the dynamic presentation of ligands, presenting a unique way to control their adhesion and spreading behavior [2].

II. Room-temperature ionic liquids (ILs) exhibit a unique set of properties due to their highly charged character, generating interest across scientific disciplines. We have been examining the combination of charged surfactants with ILs, which results in a rich interfacial behavior [3,4]. We employ traditional measures of surface activity in addition to extremely sensitive surface science techniques such as X-ray photoelectron spectroscopy. Fundamental investigations of surface thermodynamics, phase separation, kinetics, etc. are currently being revisited in the context of ILs. A more recent effort has been to explore the phase behavior of stimulus-responsive macromolecules in these novel solvents.