Domain-Selective Enzymatic Cross-linking and Etching for Shape-Morphing DNA-Linked Nanoparticle Films.

The highly programmable and responsive molecular recognition properties of DNA provide unparalleled opportunities for fabricating dynamic nanostructures capable of structural transformation in response to various external stimuli. However, they typically operate in tightly controlled environments because certain conditions (ionic strength, pH, temperature, etc.) must be met for DNA duplex formation. In this study, we adopted site-specific enzymatic ligation and DNA-based layer-by-layer thin film fabrication to build shape-morphing DNA-linked nanoparticle films operational in a broad range of environments. The ligated films remained intact in unusual conditions such as pure water and high temperature causing dissociation of DNA duplexes and showed predictable and reversible shape morphing in response to various environmental changes and DNA exchange reactions. Furthermore, domain-selective ligation combined with photoinduced interlayer mixing allowed for the fabrication of unusual edge-sealed double-layered films through midlayer etching, which is difficult to realize by other methods.

Multicolor Conjugated Polymer Thin Films with Tunable Responsivity to Oxidative and Reductive Environments.

Dynamic colors that respond to environmental changes are of great interest for diverse areas of science and technology ranging from chemical and biological sensors to smart information display. Here, we demonstrate a multitude of responsive colors from a conjugated polymer film arising from a thin-film interference. This mechanism provides an excellent control over the thin-film color by varying the film thickness, type of substrate, and degree of polaron population and is generally applicable to various conjugated polymers for further color variation. Furthermore, multiple sets of responsive colors are achieved from a single polymer layer by patterning the underlying substrate to spatially modify the interference conditions. Using this system, we demonstrate the reversible color changes induced by an oxidative or reductive environment with color responsivity controllable with the nature of the polaron state.

Free-standing two-dimensional sheets of polymer-linked nanoparticles.

Here, we report a simple and general approach to fabricate free-standing two-dimensional (2D) sheets of nanoparticles by the simultaneous self-assembly of hydrophobic nanoparticles and hydrophilic polymers at the liquid-liquid interface. The nanoparticle-polymer interaction at the interface generates well-defined 2D sheets of densely packed nanoparticles with a lateral dimension of tens of micrometers. The nanosheets transferred in water are stable over months without any additional cross-linking step. The method is applicable for a broad range of nanoparticles including oxide, semiconductor, and metal nanoparticles as well as functional polymers.

Active electrochemical high-contrast gratings as on/off switchable and color tunable pixels.

To be viable for display applications, active structural colors must be electrically tunable, on/off switchable, and reversible. Independently controlling the first two functions, however, is difficult because of causality that ties the real and imaginary parts of the optical constants or changing overlap of fields during structural variations. Here, we demonstrate an active reflective color pixel that encompasses separate mechanisms to achieve both functions reversibly by electrochemically depositing and dissolving Cu inside the dielectric grating slits on a Pt electrode with ΔV < 3 V. Varying the modal interference via Cu occupancy in the slits changes the CIE space coverage by up to ~72% under cross-polarized imaging. In the same pixel, depolarization and absorption by the dissolving porous Cu switches the color off with a maximum contrast of ~97%. Exploiting these results, we demonstrate an active color-switching display and individually addressable on/off pixel matrix that highlights their potential in reflective display applications.

Shape-Changing DNA-Linked Nanoparticle Films Dictated by Lateral and Vertical Patterns.

The self-assembly of nanoscale building blocks into complex nanostructures with controlled structural anisotropy can open up new opportunities for realizing active nanomaterials exhibiting spatiotemporal structural transformations. Here, a combination of bottom-up DNA-directed self-assembly and top-down photothermal patterning is adopted to fabricate free-standing nanoparticle films with vertical and lateral heterogeneity. This approach involves the construction of multicomponent plasmonic nanoparticle films by DNA-directed layer-by-layer (LbL) self-assembly, followed by on-demand lateral patterning by the direct photothermal writing method. The distinct plasmonic properties of nanospheres and nanorods constituting the multidomain films enable photopatterning in a selective domain with precisely controlled vertical depths. The photopatterned films exhibit complex morphing actions instructed by the lateral and vertical patterns inscribed in the film as well as the information carried in DNA.

Enhancing photoelectrochemical water splitting with plasmonic Au nanoparticles.

The water-based renewable chemical energy cycle has attracted interest due to its role in replacing existing non-renewable resources and alleviating environmental issues. Utilizing the semi-infinite solar energy source is the most appropriate way to sustain such a water-based energy cycle by producing and feeding hydrogen and oxygen. For production, an efficient photoelectrode is required to effectively perform the photoelectrochemical water splitting reaction. For this purpose, appropriately engineered nanostructures can be introduced into the photoelectrode to enhance light-matter interactions for efficient generation and transport of charges and activation of surface chemical reactions. Plasmon enhanced photoelectrochemical water splitting, whose performance can potentially exceed classical efficiency limits, is of great importance in this respect. Plasmonic gold nanoparticles are widely accepted nanomaterials for such applications because they possess high chemical stability, efficiently absorb visible light unlike many inorganic oxides, and enhance light-matter interactions with localized plasmon relaxation processes. However, our understanding of the physical phenomena behind these particles is still not complete. This review paper focuses on understanding the interfacial phenomena between gold nanoparticles and semiconductors and provides a summary and perspective of recent studies on plasmon enhanced photoelectrochemical water splitting using gold nanoparticles.

Responsive Thin-Film Interference Colors from Polaronic Conjugated Block Copolymers.

Colors responsive to the chemical environment can form the basis for simple and highly accessible diagnostic tools. Herein, the charge modulation of conjugated polymers is demonstrated as a new mechanism for chemically responsive structural colors based on thin-film interference. A liquid-liquid interfacial self-assembly is employed to create a conjugated block copolymer film that is flexible, transferable, and highly homogeneous in thickness over a large area. Gold (Au) complexes are introduced in the self-assembly process for in situ oxidation of conjugated polymers into a hole-polaronic state that renders the polymer film responsive to the chemical environment. When transferred onto a reflective substrate, the film shows thickness-dependent tunable reflective colors due to the optical interference. Furthermore, it experiences drastic changes in its dielectric behavior upon switching of the polaronic state, thereby enabling large modulations to the interferometric colors. Such responsive thin-film colors, in turn, can be used as a simple and intuitive multicolor readout for the recognition of reductive vapors including biological decomposition products.