Optical Properties of Reconfigurable Polymer/Silver Nanoprism Hybrids: Tunable Color and Infrared Scattering Contrast.

We synthesize and characterize stimulus-responsive nanocomposites consisting of poly( N-isopropylacrylamide) (PNIPAM) with controlled loadings of anisotropic plate-like silver nanoprisms. These composites show strong, reversible switching of their optical extinction and scattering properties in response to temperature cycling. We use UV-vis-NIR spectroscopy and dynamic light scattering to characterize the hybrids and show that the loading density of the silver nanoprisms in the polymer and the size of the nanoprisms are both factors that can be used to tailor the optical response of the composites, extending the range of colors beyond that previously reported with PNIPAM/plasmonic nanoparticle composites.

Dynamic Melting Properties of Photoswitch-Modified DNA: Shearing versus Unzipping.

We use dynamic force spectroscopy to study the melting properties of azobenzene-modified double-stranded DNA (azo-dsDNA) in both the shearing and unzipping geometries. By fitting the rupture force vs loading rate data with a Friddle-Noy-De Yoreo model, we extract the location of the barrier (x), the equilibrium force for the bond/transducer system (F), and the dissociation rate of dsDNA (k). We find that the k of azo-dsDNA increases after UV illumination (365 nm) in both the shearing and unzipping geometries.

Local Density Fluctuations Predict Photoisomerization Quantum Yield of Azobenzene-Modified DNA.

Azobenzene incorporated into DNA has a photoisomerization quantum yield that depends on the DNA sequence near the azobenzene attachment site. We use Molecular Dynamics computer simulations to elucidate which physical properties of the modified DNA determine the quantum yield. We show for a wide range of DNA sequences that the photoisomerization quantum yield is strongly correlated with the variance of the number of atoms in close proximity to the outer phenyl ring of the azobenzene group.

Nanoscopic Amyloid Pores Formed via Stepwise Protein Assembly.

Protein aggregation leading to various nanoscale assemblies is under scrutiny due to its implications in a broad range of human diseases. In the present study, we have used ovalbumin, a model non-inhibitory serpin, to elucidate the molecular events involved in amyloid assembly using a diverse array of spectroscopic and imaging tools such as fluorescence, laser Raman, circular dichroism spectroscopy, and atomic force microscopy (AFM). The AFM images revealed a progressive morphological transition from spherical oligomers to nanoscopic annular pores that further served as templates for higher-order supramolecular assembly into larger amyloid pores.