Yuval Ofir

Polymer and biopolymer mediated self-assembly of gold nanoparticles

Gold nanoparticle-polymer composites are versatile and diverse functional materials, with applications in optical, electronic and sensing devices. This tutorial review focuses on the use of polymers to control the assembly of gold nanoparticles. Examples of synthetic polymers and biopolymers are provided, as well as applications of the composite materials in sensing and memory devices.

Nanoimprint Lithography for Functional Three-Dimensional Patterns

Nanoimprint lithography (NIL) is viewed as an alternative nanopatterning technique to traditional photolithography, allowing micrometer-scale and sub-hundred-nanometer resolution as well as three-dimensional structure fabrication. In this Research News article we highlight current activities towards the use of NIL in patterning active or functional materials, and the application of NIL in patterning materials that present both chemistry and structure/topography in the patterned structures, which provide scaffolds for subsequent manipulation. We discuss and give examples of the various materials and chemistries that have been used to create functional patterns and their implication in various fields as electronic and magnetic devices, optically relevant structures, biologically important surfaces, and 3D particles.

Catalytic Microcapsules Assembled from Enzyme–Nanoparticle Conjugates at Oil–Water Interfaces

Involuntary association: Anionic beta-galactosidase enzymes associate with positively charged Au nanoparticles to produce reduced-charge conjugates, which assemble at oil-water interfaces to result in stable microcapsules (see picture). The microcapsules were formed quickly and showed high enzymatic activity, which makes them promising materials for biotechnology applications.

Stable Magnetic Colloidosomes via Click-Mediated Crosslinking of Nanoparticles at Water-Oil Interfaces

Alkyne- and azide-functionalized iron oxide nanoparticles are co-assembled at the water-oil interface and covalently linked using click chemistry under ambient conditions to create magnetic colloidosomes (see image). These colloidosomes possess high stability, size-selective permeability, and are responsive toward external magnetic stimuli.

Controlled Self‐Assembly of Organic Nanowires and Platelets Using Dipolar and Hydrogen‐Bonding Interactions

Synergistic dipole-dipole and hydrogen-bonding interactions are used to assemble nanostructured materials. Precipitation of a hydrogen-bonding donor-acceptor molecule 8-[[p-[bis(ethyl)amino]phenyl]azo]-isobutylflavin (ABFL) yields nanowires approximately 50-150 nm in diameter and lengths of several millimeters. Precipitation of the non-hydrogen-bonding analog, methylated ABFL (MABFL), generates micrometer-sized hexagonal platelets that are 5-10 microm in length, 1-5 microm in width, and 0.1-0.5 microm thick. The structural similarity of the two molecules allows intermediate morphologies to be formed via co-precipitation. Doping experiments demonstrate efficient control over nanowire length and diameter due to the disruption of the hydrogen bonding within the nanowires.

Chemically Directed Immobilization of Nanoparticles onto Gold Substrates for Orthogonal Assembly Using Dithiocarbamate Bond Formation

Dithiocarbamate-mediated bond formation combined with soft lithography was used for the selective immobilization of amine-functionalized silica nanoparticles on gold substrates. The available amine groups on the upper surface of the immobilized silica nanoparticles were further utilized for postdeposition of additional materials including particles, dyes, and biomolecules. The robustness of dithiocarbamate-mediated immobilization enables orthogonal assembly on surfaces via selective removal of the masking thiol ligands using iodine vapor etching followed by further functionalization.

Fabrication and Functionalization of Supramolecular Microgel Arrays Through Complementary Hydrogen-Bonding Interactions

Molecular self-assembly can be described as the thermodynamically controlled association of molecules into structurally well-defined, stable aggregates through noncovalent interactions, including van der Waals interactions, p–p stacking, electrostatics, metal coordination, and hydrogen bonding. These supramolecular interactions that define the self-assembly process are responsible for the highly ordered, diverse systems found in nature, and also provide inspiration for the creation of new self-assembled supramolecular materials. Supramolecular gels represent a particularly interesting family of self-assembled structures and are 3D networks formed by small molecules, oligomers, or polymers through noncovalent interaction linkages. These systems feature reversibility, the ability to self-heal, and selectivity compared with traditional polymer gels, and have applications in areas including biodelivery, controlled membranes, and tissue engineering. Specific interactions, such as multiple hydrogen bonding motifs and metal coordination, have been widely employed in the construction of supramolecular polymeric materials. For example, we have shown that random copolymers of polystyrene functionalized with complementary diamidopyridine (PS-DAP) and thymine (PS-Thy) moieties (Figure 1A and 1B) form supramolecular assemblies including vesicular complexes in non-competitive solvents. A key feature of these vesicular structures is that they are metastable, forming gels over the course of hours. These gels provide a potentially useful system for integrating material properties of gels with ‘lock and key’ capabilities offered by molecular recognition. Here, we demonstrate selective deposition of PS-DAP/PSThy gels onto pre-patterned silicon substrates. These microgel arrays can be crosslinked and selectively and reversibly

‘Lock and key’ control of optical properties in a push–pull system

We report the modulation of the absorbance of a flavin push-pull derivative through specific recognition by a complementary diamidopyridine (DAP), shifting the flavin intramolecular charge transfer band by approximately 30 nm.

Self-assembly of fluorocarbon-coated FePt nanoparticles for controlling structure and wettability of surfaces

Controlled self-assembly of fluorinated FePt nanoparticles from different solvent mixtures has been used to create superhydrophobic surfaces with varying topology and stickiness towards water. The ability to tune surface stickiness provides a means for fluid handling, as demonstrated by surface-to-surface transfer of water droplets.