Self-Assembly of Nanomaterials
DNA-nanoparticle assemblies at interfaces
− Structural and rheological transitions in DNA functionalized nanoparticles at interfaces:
DNA-driven assembly of nanoscale objects has emerged as a powerful platform for creation of materials by-design via self-assembly. In this project I demonstrate the use of liquid interfaces for assembly and re-organization of 2D systems of DNA-coated nanoparticles. By controlling interparticle interactions at the aqueous interface from being purely repulsive to attractive, there is phase transition from a hexagonally-ordered assembly to a string-like cluster morphology of NPs and finally to a percolating network. The in-situ and ex-situ structural transition measured by grazing incidence small x-ray scattering (GISAXS) and SEM respectively is accompanied by significant change in the mechanical behavior of the interface. The rheological properties of the nanoparticle layer measured by interfacial rheology change from being viscous to viscoelastic and to elastic depending on the 2D assembly morphology and interaction of NP monolayer with the lipid interface. The demonstrated methodology for the assembly of 2D DNA-programmable systems at liquid interfaces opens the possibility for the creation of nanoparticle membranes with regulated network topology and mechanical properties.
− Bio-molecule based pH responsive 2D nanocrystals:
The special pairing capability of DNA such as pH induced transformation in i-motifs have been utilized for several nanoparticle assemblies. By designing component of the DNA corona with A-rich nucleotides I have developed 2D nanocrystals with response properties with change in pH of the medium. The DNA nanoparticle organize in 2D hexagonal crystalline structure where nanoparticle are not connected but held by repulsive potential due to polymeric nature of DNA chains and electrostatic interaction between DNA chains grafted at the nanoparticle at neutral or basic pH. At acidic pH the protonation of hydrogen bond results in formation of connected HCP structure with reduced lattice. The structural response of the 2D crystal measured by in-situ GISAXS is reversible over several cycle of change in pH of the medium an excellent method to use these systems as pH sensor in biological physiological environment. I believe these nano-crystals can be potentially used as pH sensor for 2D systems due to its significant structural response with change in pH via decrease in the lattice constant of the crystalline assembly.
Super-compressible DNA nanoparticle lattices
The compression properties of DNA-nanoparticle assemblies were studied by measuring their response to applied osmotic pressure. The lattices of nanoparticles interconnected with DNA exhibit an affine transformation under compression with a remarkably strong decrease of the lattice constant, up to a factor of about 1.8, corresponding to above 80% of the volume reduction. Using in-situ small angle x-ray scattering, (SAXS) and optical microscopy, I studied the DNA-induced effective interparticle interactions by measuring the macroscopic and nanoscale compression behaviors as a function of applied osmotic stress. The force field extracted from experimental data can be well described by a theoretical model that takes into account confinement of DNA chains in interstitial regions. The compression properties of can be tuned via DNA molecular design