Sreenath Bolisetty

Water-soluble organo-silica hybrid nanowires.

There has been growing interest in the past decade in one-dimensional (1D) nanostructures, such as nanowires, nanotubes or nanorods, owing to their size-dependent optical and electronic properties and their potential application as building blocks, interconnects and functional components for assembling nanodevices. Significant progress has been made; however, the strict control of the distinctive geometry at extremely small size for 1D structures remains a great challenge in this field. The anisotropic nature of cylindrical polymer brushes has been applied to template 1D nanostructured materials, such as metal, semiconductor or magnetic nanowires. Here, by constructing the cylindrical polymer brushes themselves with a precursor-containing monomer, we successfully synthesized hybrid nanowires with a silsesquioxane core and a shell made up from oligo(ethylene glycol) methacrylate units, which are soluble in water and many organic solvents. The length and diameter of these rigid wires are tunable by the degrees of polymerization of both the backbone and the side chain. They show lyotropic liquid-crystalline behaviour and can be pyrolysed to silica nanowires. This approach provides a route to the controlled fabrication of inorganic or hybrid silica nanostructures by living polymerization techniques.

Amyloid-carbon hybrid membranes for universal water purification.

Industrial development, energy production and mining have led to dramatically increased levels of environmental pollutants such as heavy metal ions, metal cyanides and nuclear waste. Current technologies for purifying contaminated waters are typically expensive and ion specific, and there is therefore a significant need for new approaches. Here, we report inexpensive hybrid membranes made from protein amyloid fibrils and activated porous carbon that can be used to remove heavy metal ions and radioactive waste from water. During filtration, the concentration of heavy metal ions drops by three to five orders of magnitude per passage and the process can be repeated numerous times. Notably, their efficiency remains unaltered when filtering several ions simultaneously. The performance of the membrane is enabled by the ability of the amyloids to selectively absorb heavy metal pollutants from solutions. We also show that our membranes can be used to recycle valuable heavy metal contaminants by thermally reducing ions trapped in saturated membranes, leading to the creation of elemental metal nanoparticles and films.

Direct Observation of Time‐Resolved Polymorphic States in the Self‐Assembly of End‐Capped Heptapeptides

Amyloid fibrils resulting from uncontrolled peptide aggregation are associated with several neurodegenerative diseases. Their polymorphism depends on a number of factors including pH, ionic strength, electrostatic interactions, hydrophobic interactions, hydrogen bonding, aromatic stacking interactions, and chirality. Understanding the mechanism of amyloid fibril formation can improve strategies towards the prevention of fibrillation processes and enable a wide range of potential applications in nanotemplating and nanotechnology.

Hybrid Nanocomposites of Gold Single‐Crystal Platelets and Amyloid Fibrils with Tunable Fluorescence, Conductivity, and Sensing Properties

Gold single-crystal platelets with high aspect ratio are combined with amyloid fibrils to design a new class of hybrid nanocomposites. The films gather physical properties from both constituents, for example, plasmon resonance, fluorescence, and water-dependent conductivities ranging from insulating to metallic levels, yet mirroring gold within a broad range of composition, and can serve multiple purposes such as sensors, diagnostic, printed electronics, micromechanical, and biological devices.

Snapshots of fibrillation and aggregation kinetics in multistranded amyloid β-lactoglobulin fibrils

We have investigated the structural time-evolution of multistranded β-lactoglobulin protein fibrils at pH 2 and 90 °C by combining small angle neutron scattering (SANS), dynamic (DLS) and depolarized light scattering (DDLS) as well as atomic force microscopy (AFM). Light scattering techniques, combined with SANS clearly demonstrate the different stages of conversion of β-lactoglobulin monomers (2 wt %) into semiflexible protein fibrils upon heating at 90 °C. In addition, atomic force microscopy allows the resolution of some details of the fibrils at the molecular length scale which bulk scattering techniques cannot capture. Thus, we were able to resolve and identify different individual stages of the fibrillation process, including the formation of protofilaments, their alignment and aggregation into mature multistranded fibrils, and the development of a periodic pitch along their contour length. The picture emerging from combination of the scattering and single molecule techniques is consistent with three critical steps: (i) individual protofilaments align upon approaching due to liquid crystalline interactions; (ii) short range attractions among filaments—presumably of Lennard–Jones or hydrophobicity type—lead to irreversible aggregation of nearly perfectly aligned protofilaments into multistranded ribbon-like fibrils; (iii) intramolecular electrostatic repulsion of fibrils leads to twisting of the ribbon along the axis leading to the development of a periodic pitch along the fibrils contour length. The individual stages of the fibrillation and aggregation process are discussed in detail, in terms of the colloidal physics involved.

Self-Assembly of Ovalbumin into Amyloid and Non-Amyloid Fibrils

We study the fibrillation pathway of ovalbumin protein and report the simultaneous formation of several types of fibrils, with clear structural and physical differences. We compare the fibrillation mechanisms at low pH with and without salt, and follow the kinetics of fibrils growth by atomic force microscopy (AFM), static and dynamic light scattering (SLS, DLS), and small-angle X-ray scattering (SAXS). We show that, among the morphologies identified, long semiflexible amyloid fibrils (type I), with persistence length Lp∼3 μm, Youngs modulus E∼2.8 GPa, and cross-β structure are formed. We also observe much more flexible fibrils (type III, Lp∼63 nm), that can assemble into multistranded ribbons with time. They show significantly lower intrinsic stiffness (1.1 GPa) and a secondary structure, which is not characteristic of the well-ordered amyloids, as determined by circular dichroism (CD), wide-angle X-ray scattering (WAXS), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). In between these two main classes of fibrils, a third family, with intermediate flexibility (type II, Lp∼300 nm), is also resolved.

Hierarchically Structured Microfibers of “Single Stack” Perylene Bisimide and Quaterthiophene Nanowires

Organic nanowires and microfibers are excellent model systems for charge transport in organic semiconductors under nanoscopic confinement and may be relevant for future nanoelectronic devices. For this purpose, however, the preparation of well-ordered organic nanowires with uniform lateral dimensions remains a challenge to achieve. Here, we used the self-assembly of oligopeptide-substituted perylene bisimides and quaterthiophenes to obtain well-ordered nanofibrils. The individual nanofibrils were investigated by spectroscopic and imaging methods, and the preparation of hierarchically structured microfibers of aligned nanofibrils allowed for a comprehensive structural characterization on all length scales with molecular level precision. Thus, we showed that the molecular chirality resulted in supramolecular helicity, which supposedly serves to suppress lateral aggregation. We also proved that, as a result, the individual nanofibrils comprised a single stack of the π-conjugated molecules at their core. Moreover, the conformational flexibility between the hydrogen-bonded oligopeptides and the π-π stacked chromophores gave rise to synergistically enhanced strong π-π interactions and hydrogen-bonding. The result is a remarkably tight π-π stacking inside the nanofibrils, irrespective of the electronic nature of the employed chromophores, which may render them suitable nanowire models to investigate one-dimensional charge transport along defined π-π stacks of p-type or n-type semiconductors.

Macroscopic Alignment of Lyotropic Liquid Crystals Using Magnetic Nanoparticles

A versatile approach to align anisotropic mesophases in the presence of magnetic nanoparticles in response to an external magnetic field is demonstrated. A memory effect is shown, as the alignment of the nanoparticles, the mesophase, and the overall birefringence can be stored, erased, and rewritten reversibly by changing the temperature and the direction of the external magnetic field.

Amyloid Templated Gold Aerogels

Amyloid fibril-based ultralow-density aerogels are designed by functionalization with gold nanoparticles and microcrystals, leading to hybrids of unprecedented lightness and functionality. By changing the colloidal gold shape, size, and concentration, the gold composition can be tuned to reach contents ≥20 kt equivalent, yet at densities ≈10(3) lighter than any equivalent gold alloys, and combining unique features such as porosity, catalytic properties, pressure sensing, and autofluorescence.

Switching the morphologies of cylindrical polycation brushes by ionic and supramolecular inclusion complexes.

Cylindrical polycation brushes form an ionic complex with surfactant sodium dodecyl sulfate (SDS) in aqueous solution, which causes a worm-to-sphere collapse of the brush. Alpha- and beta-cyclodextrin (CD) returns the brush to the worm-like conformation by forming a supramolecular inclusion complex with SDS. When beta-CD was employed for the inclusion complex, addition of 1-adamantylammonium chloride releases SDS by forming a stronger inclusion complex, causing the recollapse of the brush to spheres.