Synthesis of Linear Black Gold Nanostructures Processable as Sunlight and Low-Energy Light Collecting Films for Photo-Thermoelectricity.

As one of the effort to cope with the energy crisis and carbon neutrality, utilization of low-grade energy generated indoors (e.g., light) is imperative because this saves building and house energy, which accounts for ≈40% of total energy consumption. Although photovoltaic devices could contribute to energy savings, it is also necessary to harvest heat from indoor lights to generate electricity because the light absorbed by materials is mostly transformed into heat. For daily life uses, materials should not only have high absorptance and low emittance but also be easily processed into various forms. To this end, this work synthesizes black aqueous suspensions containing winding and bent linear gold nanostructures with diameters of 3-5 nm and length-to-diameter ratios of ≈4-10. Their optical and photo-thermal characteristics are understood through experimental and theoretical investigations. Black gold nanostructures are conveniently processed into metal-dielectric films on metal, glass, and flexible substrates. The film on copper has an absorptance of 0.97 and an emittance of 0.08. Under simulated sunlight and indoor LED light illumination, the film has equivalent photo-thermal and photo-thermoelectric performances to a top-tier sunlight-collecting film. This work attempts to modify the film structure to generate more usable electricity from low-energy indoor light.

Reaction-Based Scalable Inorganic Patterning on Rigid and Soft Substrates for Photovoltaic Roofs with Minimal Optical Loss and Sustainable Sunlight-Driven-Cleaning Windows.

Recently developed fabrication methods for inorganic patterns (such as laser printing and optical lithography) can avoid some patterning processes conducted by conventional etching and lithography (such as substrate etching and modulation) and are thereby useful for applications in which the substrates and materials must not be damaged during patterning. Simultaneously, it is also necessary to develop facile and economical methods producing inorganic patterns on various substrates without requiring a special apparatus while attaining the above-mentioned advantages. The present study proposes a reaction-based method for fabricating inorganic patterns by immersing substrates coated with a colloidal nanosheet into an aqueous solution containing inorganic precursors. Silica and TiO2 patterns spontaneously developed during the conversion of each inorganic precursor. These patterns were successful on rigid and flexible substrates. We fabricated these patterns on a wafer-sized silicon and large flexible poly(ethylene terephthalate) film, suggesting the scalability. We fabricated a biomimetic pattern on both sides of a glass window, as a photovoltaic roof, for minimal optical losses to maximally present photovoltaic effects of a solar cell. The TiO2 pattern on glass window exhibits sustainable sunlight-driven-cleaning activity for contaminants. The method could provide a platform for economical high-performance inorganic patterns for energy, environmental, electronics, and other areas.

Optically Left-Handed Nanopearl Beads with Inductance-Capacitance Circuits at Visible-Near-Infrared Frequencies Based on Scalable Methods.

Optically left-handed materials refract the propagating light in the opposite direction. Most research has focused on the design of various structures, including split-ring resonators, either on planes or in particle cluster forms to resonate with specific light frequencies. However, for particle-based materials, the circuital structures for optical left-handedness have not been fully understood and the effect of interior structure on the optical handedness have not been investigated. Additionally, scalable methods to deploy the unique characteristics of the materials have not been reported so far and are still urgent. Here, optically left-handed nanopearl beads are synthesized in up to 1.25 L solutions. Nanopearl beads contain assembled Au nanocolloids, a dielectric sphere, and a thin silica layer that fixes the assembled structures to sustainably yield unique inductance-capacitance circuits at specific visible-near-infrared frequencies. The frequencies are tunable by modulating the interior structures. Investigation of the circuit structures and Poynting vectors generated within the nanopearl beads suggest the likelihood of their left-handedness. Moreover, the effects of interior structures on the optical handedness of the nanopearl beads are extensively investigated. The results could help commercialize optically left-handed materials and pioneer fields that have not been realized so far.

Detection of Lysyl Oxidase Activity in Tumor Extracellular Matrix Using Peptide-Functionalized Gold Nanoprobes.

High LOX levels in the tumor microenvironment causes the cross-linking of extracellular matrix components and increases the stiffness of tumor tissue. Thus, LOX plays an important role in tumorigenesis and in lowering the tumor response to anticancer drugs. Despite comprehensive efforts to identify the roles of LOX in the tumor microenvironment, sensitive and accurate detection methods have not yet been established. Here, we suggest the use of gold nanoparticles functionalized with LOX-sensitive peptides (LS-AuNPs) that aggregate upon exposure to LOX, resulting in a visual color change. LOX-sensitive peptides (LS-peptides) contain lysine residues that are converted to allysine in the presence of LOX, which is highly reactive and binds to adjacent allysine, resulting in the aggregation of the AuNPs. We demonstrated that the synthesized LS-AuNPs are capable of detecting LOX sensitively, specifically both in vitro and in the tissue extract. Moreover, the suggested LS-AuNP-based assay is more sensitive than commonly employed assays or commercially available kits. Therefore, the LS-AuNPs developed in this study can be used to detect LOX levels and can be further used to predict the stiffness or the anticancer drug resistance of the tumor.

Hydrochromic Smart Windows to Remove Harmful Substances by Mimicking Medieval European Stained Glasses.

Medieval European stained glass windows are known to display various splendid colors and remove harmful airborne substances. At present, the functions of medieval stained glass windows are imperative, from the environment, health, and energy perspectives, to develop multi-functional windows that report/control environmental conditions and remove harmful substances by utilizing visible-near-infrared light sources. Here, we suggest a strategy to mimic medieval European stained glasses for devising plasmonic-based multi-functional smart stained glass windows. The stained glass windows are prepared from the deposition of gold nanoparticles on a glass that is preliminarily coated with a responsive colloidal nanosheet. The temperature responsiveness of the nanosheet enables the effective control the gold nanoparticle density of the stained glasses. Therefore, the windows can display blue, violet, and cranberry colors. The colors become iridescent by introducing a photonic crystal monolayer. The stained glass windows are hydrochromic: they switch the colors (blue ↔ cranberry) and modulate light transmittance depending on humidity conditions. Moreover, they can remove formaldehyde under the illumination of a low-power indoor light. These functions provide a new platform for the futuristic smart windows that clean indoor air for the human health and save energy.

Flow Behaviors of Polymer Colloids and Curing Resins Affect Pore Diameters and Heights of Periodic Porous Polymer Films to Direct Their Surface and Optical Characteristics.

Manipulation of both pore diameters and heights of two-dimensional periodic porous polymer films is important to extensively control their characteristics. However, except for using different sized colloid templates in replication methods, an effective method that tunes these factors has rarely been reported. We found that both parameters are controllable by adjusting the flow behaviors of polystyrene colloids and curing resin precursors during the preparation of phenolic resin and poly(dimethylsiloxane) periodic porous films by embedding their precursors into colloidal crystal monolayers. We adjust the flow behaviors by either varying film preparation temperatures (≥glass transition temperature of polystyrene) or using the precursors mixed with different amounts of solvents that renders the colloids viscous. Consequently, the pore diameters and film heights change by 36-56 and 56-84%, respectively. Such modulation results in the change in height to diameter ratios and the areal fractions of resins at air-film interfaces, thereby significantly changing the water contact angles on these surfaces and their photonic characteristics. This straightforward method does not require additional steps, differently sized colloids, or different amounts of precursors for these parameter controls.

Solution-Processed Plasmonic-Dielectric Sunlight-Collecting Nanofilms for Solar Thermoelectric Application.

It is important but remains a challenge to develop solution-processed plasmonic solar thermoelectricity films on various substrates, without strictly considering hierarchical plasmonic-dielectric-metal structures, to harvest a wide range of visible to near-infrared sunlight. We simply fabricate plasmonic silica metastructure sunlight-collecting nanofilms on highly reflective Cu and Si surfaces by introducing spin coating (with an Ag and silica colloidal mixture, a spin coater, and a heating plate) and low-temperature annealing (in an oven at 200 °C for 1 h) processes. The approximately 250 nm thick metastructure consists of a top 60 nm thick silica layer as an antireflective film and a bottom 190 nm thick Ag nanoparticle-silica hybrid film as a sunlight harvester. The metastructure film reduces the reflectivity of Cu (>90%) and Si (25-35%) to less than 5% at visible to near-infrared frequencies. The metastructure film on the Cu sheet has an absorptance of 0.95 and a thermal emittance of 0.06, ideal for high-performance sunlight absorbers. The solar thermoelectric powers of the film-coated Cu and Si are 15.4 and 4.7 times those of the uncoated Cu and Si substrates, respectively. The metastructure film on Cu exhibited a similar or slightly higher performance than that of a top-class vapor-deposited commercialized absorber film on Cu, demonstrating the robustness of the present method.

A Hierarchically Modified Graphite Cathode with Au Nanoislands, Cysteamine, and Au Nanocolloids for Increased Electricity-Assisted Production of Isobutanol by Engineered Shewanella oneidensis MR-1.

It is necessary to understand the surface structural effects of electrodes on the bioalcohol productivity of Shewanella oneidensis MR-1, but this research area has not been deeply explored. Here, we report that the electricity-assisted isobutanol productivity of Shewanella oneidensis MR-1::pJL23 can be enhanced by sequentially modifying a graphite felt (GF) surface with Au nanoislands (Au), cysteamine (NH2), and Au nanoparticles (Au NPs). After bacteria were incubated for 50 h with the unmodified GF under various electrode potentials (vs Ag/AgCl), the bacterial isobutanol concentrations increased from 2.9 ± 1 mg/L under no electricity supply to a maximum of 5.9 ± 1 mg/L at -0.6 V. At this optimum electrode potential, the concentrations continued increasing to 9.1 ± 1, 14 ± 2, and 27 ± 2 mg/L when the GF electrodes were modified with Au, NH2-Au, and Au NP-NH2-Au, respectively. We further studied how each surface structure affected the bacterial adsorptions, current profiles, and biofilms' electrochemical performances. In particular, these modifications induced the adsorption of elongated bacteria, with the amount dependent on the electrode structure. In the presence of electric supply, the amount of elongated bacteria further increased. We also found that the NH2-Au-GF and Au NP-NH2-Au-GF electrodes themselves could increase the concentrations to 11 ± 0.3 and 12 ± 2 mg/L, respectively, upon the bacterial incubation without electricity. Among the electrodes tested, the contribution of electricity to the bacterial isobutanol production was the greatest with the Au NP-NH2-Au-GF electrode. After 96 h of incubation, the concentration increased to 72 ± 2 mg/L, which was 4.7 and 3.7 times the previously reported values obtained without and with electricity, respectively.

Nanoscale Structural Switching of Plasmonic Nanograin Layers on Hydrogel Colloidal Monolayers for Highly Sensitive and Dynamic SERS in Water with Areal Signal Reproducibility.

Developing substrates that enable both reproducible and highly sensitive Raman detection of trace amounts of molecules in aqueous systems remains a challenge, although these substrates are crucial in biomedicine and environmental sciences. To address this issue, we report spatially uniform plasmonic nanowrinkles formed by intimate contact between plasmonic nanograins on the surface of colloidal crystal monolayers. The Au or Ag nanograin layers coated on hydrogel colloidal crystal monolayers can reversibly wrinkle and unwrinkle according to changes in the water temperature. The reversible switches are directed by surface structural changes in the colloidal crystal monolayers, while the colloids repeat the hydration-dehydration process. The Au and Ag nanowrinkles are obtained upon hydration, thus enabling the highly reproducible detection of Raman probes in water at the nano- and picomolar levels, respectively, throughout the entire substrate area. Additionally, the reversible switching of the nanostructures in the plasmonic nanograin layers causes reversible dynamic changes in the corresponding Raman signals upon varying the water temperature.

A Surfactant-Free and Shape-Controlled Synthesis of Nonspherical Janus Particles with Thermally Tunable Amphiphilicity.

A surfactant-free approach is proposed to synthesize nonspherical Janus particles with temperature-dependent wettability on hydrophobic surfaces. Sub-micrometer-sized particles comprising poly(styrene-co-divinylbenzene) core and a thermally responsive poly(N-isopropylacrylamide-co-methacrylic acid) shell are first synthesized to stabilize styrene droplets in water, producing a Pickering emulsion. Upon heating to 80 °C and subsequent addition of initiators to the aqueous phase, styrene droplets are polymerized and combine with the core-shell particles to construct dumbbell-shaped nonspherical particles. The shape of the nonspherical particles is controllable by adjusting the equilibrium time of the Pickering emulsion at 80 °C, which is conducted prior to polymerization. The mechanism of formation is discussed in more detail. Since molecular surfactants or stabilizers are not used during the synthesis, the present nonspherical particles well exhibit their own temperature-dependent amphiphilic characteristics. The aqueous dispersion containing the dumbbell-shaped particles alters its wettability on hydrophobic polymer surfaces according to temperature changes, demonstrating its temperature-dependent amphiphilicity change.

Dual-responsive and Multi-functional Plasmonic Hydrogel Valves and Biomimetic Architectures Formed with Hydrogel and Gold Nanocolloids.

We present a straightforward approach with high moldability for producing dual-responsive and multi-functional plasmonic hydrogel valves and biomimetic architectures that reversibly change volumes and colors in response to temperature and ion variations. Heating of a mixture of hybrid colloids (gold nanoparticles assembled on a hydrogel colloid) and hydrogel colloids rapidly induces (within 30 min) the formation of hydrogel architectures resembling mold shapes (cylinder, fish, butterfly). The biomimetic fish and butterfly display reversible changes in volumes and colors with variations of temperature and ionic conditions in aqueous solutions. The cylindrical plasmonic valves installed in flow tubes rapidly control water flow rate in on-off manner by responding to these stimuli. They also report these changes in terms of their colors. Therefore, the approach presented here might be helpful in developing new class of biomimetic and flow control systems where liquid conditions should be visually notified (e.g., glucose or ion concentration changes).

Plasmonic-based colorimetric and spectroscopic discrimination of acetic and butyric acids produced by different types of Escherichia coli through the different assembly structures formation of gold nanoparticles.

We present a plasmonic-based strategy for the colourimetric and spectroscopic differentiation of various organic acids produced by bacteria. The strategy is based on our discovery that particular concentrations of dl-lactic, acetic, and butyric acids induce different assembly structures, colours, and optical spectra of gold nanoparticles. We selected wild-type (K-12 W3110) and genetically-engineered (JHL61) Escherichia coli (E. coli) that are known to primarily produce acetic and butyric acid, respectively. Different assembly structures and optical properties of gold nanoparticles were observed when different organic acids, obtained after the removal of acid-producing bacteria, were mixed with gold nanoparticles. Moreover, at moderate cell concentrations of K-12 W3110 E. coli, which produce sufficient amounts of acetic acid to induce the assembly of gold nanoparticles, a direct estimate of the number of bacteria was possible based on time-course colour change observations of gold nanoparticle aqueous suspensions. The plasmonic-based colourimetric and spectroscopic methods described here may enable onsite testing for the identification of organic acids produced by bacteria and the estimation of bacterial numbers, which have applications in health and environmental sciences.

Use of fluorescence signals generated by elastic scattering under monochromatic incident light for determining the scattering efficiencies of various plasmonic nanoparticles.

We present a route that estimates the scattering/absorption characteristics of plasmonic nanoparticles by using fluorescence and UV-visible spectroscopy. Because elastic scattering of nanoparticles caused by a monochromatic incident light is reflected in fluorescence emission spectra when recording at the excitation wavelength, the scattering intensities at the excitation wavelength during fluorescence emission scans are used to compare the scattering characteristics of various plasmonic nanoparticles under conditions where the extinction values of all of the nanoparticles are kept constant at this wavelength. For the two excitation wavelengths (519 and 560 nm) we investigated, the scattering intensities of spherical gold nanoparticles increase with increasing size (15, 33, 51, 73, and 103 nm in diameter). These results are correlated with the nanoparticles' scattering efficiencies (the ratios of scattering to the extinction cross-sections), which are theoretically calculated in the literature using Mie theory. Then, linear calibration equations at each wavelength are derived to estimate the scattering efficiencies of two Au nanorods, Au nanocages, and spherical Ag nanoparticles (15, 25, 37, and 62 nm). The values are very comparable with literature values. For various purposes such as biomedicine and optoelectronics, the present method could be beneficial to those who wish to easily compare and determine the scattering characteristics of various plasmonic nanoparticles at a certain wavelength by using commercially-available spectroscopic techniques.

A Simple Evaporation Method for Large-Scale Production of Liquid Crystalline Lipid Nanoparticles with Various Internal Structures.

We present a simple and industrially accessible method of producing liquid crystalline lipid nanoparticles with various internal structures based on phytantriol, Pluronic F127, and vitamin E acetate. Bilayer vesicles were produced when an ethanolic solution dissolving the lipid components was mixed with deionized water. After the evaporation of ethanol from the aqueous mixture, vesicles were transformed into lipid-filled liquid crystalline nanoparticles with well-defined internal structures such as hexagonal lattices (mostly inverted cubic Pn3m), lined or coiled pattern (inverted hexagonal H2), and disordered structure (inverse microemulsion, L2), depending on the compositions. Further studies suggested that their internal structures were also affected by temperature. The internal structures were characterized from cryo-TEM and small-angle X-ray scattering results. Microcalorimetry studies were performed to investigate the degree of molecular ordering/crystallinity of lipid components within the nanostructures. From the comparative studies, we demonstrated the present method could produce the lipid nanoparticles with similar characteristics to those made from a conventional method. More importantly, the production only requires simple tools for mixing and ethanol evaporation and it is possible to produce 10 kg or so per batch of aqueous lipid nanoparticles dispersions, enabling the large-scale production of the liquid crystalline nanoparticles for various biomedical applications.

Attomolar Level Detection of Raman Molecules with Hierarchical Silver Nanostructures Including Tiny Nanoparticles between Nanosized Gaps Generated in Silver Petals.

We developed a route for synthesizing Ag nanostructures with tunable morphologies for ultrasensitive surface-enhanced Raman spectroscopy. Through the consecutive addition of three reducing agents (i.e., 4-mercaptobenzoic acid, trisodium citrate, and ascorbic acid) to an aqueous solution of silver nitrate, hierarchical flower-like Ag nanostructures were produced. The nanostructures had Ag petals in which nanosized gaps were generated, and small Ag nanoparticles were incorporated within the gaps. Theoretically, the nanostructures exhibited highly enhanced electric fields in the outer-shell regions where the small Ag nanoparticles were densely located. Combining the enhanced field effect with resonance effect of a Raman-active molecule (methylene blue) at a specific wavelength, measurable Raman signals were obtained at concentrations as low as 100 attomolar (10(-16) M; corresponding to 10(-21) mol). Key factors were discussed for the synthesis of the Ag nanostructures while finely controlling the morphologies of hierarchical Ag nanostructures, thereby modulating the intensity of surface-enhanced resonance Raman spectroscopy (SERRS) signals. Therefore, this synthetic method produces highly promising nanostructures for SERRS-based applications.

Manipulation of silver nanocubes detection sensitivity to radical compounds by modifying their surfaces with anionic/cationic polyelectrolytes for wide-range quantification of radicals.

We report a method for controlling the detection sensitivity to or the degree of etching of Ag nanocubes by radicals by modifying their surfaces with poly(acrylic acid) or poly(allylamine hydrochloride) for wide-range quantification of radical compounds. The degree of Ag nanocube etching is influenced by the concentrations of the polyelectrolytes used for modification. These polyelectrolytes protect the Ag nanocubes, probably by either retarding (forming diffusion barriers) or preventing (blocking/entrapping/scavenging) the arrival of radicals to Ag nanocubes, or both. The weights of the two roles are different depending on the polyelectrolyte type; therefore, the sensitivities of Ag nanocubes are also influenced by this factor. The roles of the polyelectrolytes were demonstrated by using radical compounds produced from tetrahydrofuran and H2O2 and further confirmed with Ag nanospheres. Using the results, the radical sensitivities and detection ranges of polyelectrolyte-modified Ag nanoparticles could be manipulated. Moreover, we produced calibration curves for the wide-range quantification of radical compounds.

Fabrication of pseudo-ceramide-based lipid microparticles for recovery of skin barrier function.

The recovery of skin barrier functions was investigated with pseudo-ceramide-based lipid microparticles. The microparticles were prepared by using a fluid bed technique where lipid components (a pseudo-ceramide, cholesterol and a fatty acid) were coated on a sugar seed, and a polymer was subsequently coated on the lipid microparticles. The microparticles contained large amount of pseudo-ceramide, and the pseudo-ceramide was in the form of lamellar structures mixed with other lipid components. In addition, the microparticles were stably dispersed in aqueous media or emulsion systems without any disruption of the microparticles' structures, thereby supplying sufficient amount of the pseudo-ceramide to skins for improving skin barrier functions such as preventing water loss. Such a role of the microparticles was proven by evaluating in vivo the efficacy of the lipid microparticles in reducing a trans-epidermal water loss (TEWL) of impaired murine skins. As a result, the novel pseudo-ceramide-based lipid microparticles for barrier recovery may potentially be applied in the field of dermatology, cosmetics and pharmaceuticals.

Gold nanocages: from synthesis to theranostic applications.

Gold nanostructures have garnered considerable attention in recent years for their potential to facilitate both the diagnosis and treatment of cancer through their advantageous chemical and physical properties. The key feature of Au nanostructures for enabling this diverse array of biomedical applications is their attractive optical properties, specifically the scattering and absorption of light at resonant wavelengths due to the excitation of plasmon oscillations. This phenomenon is commonly known as localized surface plasmon resonance (LSPR) and is the source of the ruby red color of conventional Au colloids. The resonant wavelength depends on the size, shape, and geometry of the nanostructures, providing a set of knobs to manipulate the optical properties as needed. For in vivo applications, especially when optical excitation or transduction is involved, the LSPR peaks of the Au nanostructures have to be tuned to the transparent window of soft tissues in the near-infrared (NIR) region (from 700 to 900 nm) to maximize the penetration depth. Gold nanocages represent one class of nanostructures with tunable LSPR peaks in the NIR region. These versatile nanostructures, characterized by hollow interiors and ultrathin, porous walls, can be prepared in relatively large quantities using a remarkably simple procedure based on the galvanic replacement between Ag nanocubes and aqueous chloroauric acid. The LSPR peaks of Au nanocages can be readily and precisely tuned to any wavelength in the NIR region by controlling their size, wall thickness, or both. Other significant features of Au nanocages that make them particularly intriguing materials for biomedical applications include their compact sizes, large absorption cross sections (almost five orders of magnitude greater than those of conventional organic dyes), and their bio-inertness, as well as a robust and straightforward procedure for surface modification based on Au-thiolate chemistry. In this Account, we present some of the most recent advances in the use of Au nanocages for a broad range of theranostic applications. First, we describe their use as tracers for tracking by multiphoton luminescence. Gold nanocages can also serve as contrast agents for photoacoustic (PA) and mutimodal (PA/fluorescence) imaging. In addition, these nanostructures can be used as photothermal agents for the selective destruction of cancerous or diseased tissue. Finally, Au nanocages can serve as drug delivery vehicles for controlled and localized release in response to external stimuli such as NIR radiation or high-intensity focused ultrasound (HIFU).