Near-Infrared-Excitable SERS Measurement Using Magneto-Responsive Metafluids for in Situ Molecular Analysis

Metal nanoparticle clusters are regarded as metamaterials, and dispersions of nanoparticle clusters are regarded as metafluids. Surface-enhanced Raman scattering (SERS) from molecules adsorbed on the nanoparticle clusters is one of the notable properties of metafluids. SERS is expected to permit the realization of single-molecule detection in chemical and biological samples, especially cells and tissues. However, most SERS measurements have been done on substrates; local information on cells and tissues have been hard to obtain. SERS active particles can be used to measure the local information on cells. To analyze biological samples using SERS, the SERS substrate should be excitable in the near-infrared (NIR) region to ensure high transparency in biological tissues. Furthermore, transporting the SERS particles to the desired position is crucial for obtaining high resolution. Sizes of SERS-active particles also affect to the resolutions. In this report, gold nanoparticle clusters based on polymer core–shell particles incorporating magnetic Fe3O4 nanoparticles were prepared via a self-assembly method. Structures, LSPR absorption, SERS signals, magnetic responsibility of prepared particles were analyzed by electron microscope, UV–vis spectrum, Raman measurement, and optical microscope observation under magnetic flux, respectively. The enhancement factor of the SERS signal was determined by the size of composited gold nanoparticles. Furthermore, the migration direction of the gold nanoparticle cluster composite particles in aqueous media was successfully controlled by the application of an external magnetic field

Atomic Layer Deposition of HfO₂ Films Using Tetrakis(1‑(<i>N</i>,<i>N</i>‑dimethylamino)-2-propoxy)hafnium [Hf(dmap)₄] for Advanced Gate Dielectrics Applications

Atomic layer deposition (ALD) of HfO2 thin films was studied by using a novel Cl-free hafnium ALD precursor: tetrakis(1-(N,N-dimethyl­amino)-2-propoxy)­hafnium [Hf(dmap)4]. This precursor is a liquid at room temperature and has been shown by differential scanning calorimetry (DSC) analysis to be stable at temperatures as high as 371 °C. Compared with the conventional Hf precursor tetrakis(ethyl­methylamido)­hafnium(IV) (TEMAH), Hf(dmap)4 exhibits a substantially greater decomposition temperature because of its alkoxide structure. Hf(dmap)4 is a volatile compound that shows a very clean thermogravimetry curve without decomposition or residue formation at 10 Torr. We performed ALD of HfO2 using Hf(dmap)4 with an oxidant of either O3 or H2O as an oxidant. As the wafer temperature was increased from 250 to 400 °C, the film growth rate slightly increased from 0.35 to 0.55 Å/cycle. Therefore, Hf(dmap)4 can be used for ALD at higher deposition temperatures than for TEMAH. However, the film growth rate was lowered by the sterically hindered ligand structure of the precursor. We evaluated the saturation behavior of the growth rate in experiments in which the Hf(dmap)4 supply time was varied from 5 to 30 s. As a result, a constant film growth rate was observed because of ALD saturation when the precursor supply time was 10 s or longer in the temperature range 350–400 °C. This result indicates that Hf(dmap)4 was not decomposed and behaved as an ALD precursor at 400 °C. We concluded that Hf(dmap)4 is a promising precursor for high-temperature ALD of HfO2 film for gate dielectrics, high-K capacitors, and HfO2-based ferroelectrics

A New Concept for an Adhesive Material Inspired by Clingfish Sucker Nanofilaments

Underwater adhesive materials are in high demand in various fields, and fish species with sucker disks have attracted attention due to their superior performance and interesting structures. The clingfish, in particular, is widely known for using hierarchical sucker disk structures to demonstrate rapid and strong adhesion to rocky surfaces under strong currents. We examined the combination of nanofilaments and mucus in the clingfish sucker disk. Nanofilaments reinforce mucus adhesion force by reducing the compliance without affecting the contact area. We prepared structures from hard polymers and soft polydimethylsiloxane (PDMS) that mimicked clingfish sucker nanofilaments and mucus, with these biomimetic structures showing significant adhesion force underwater. Furthermore, the hardness and length of the nanofilaments and Young’s modulus and thickness of the mucus-mimicking PDMS layer had critical effects on the adhesion force. According to the results, clingfish nanofilaments act as hard bracing for the soft mucus, and the structural combination of the conflicting characteristics of hardness and softness, thus achieved, is crucial for strong adhesion

A New Concept for an Adhesive Material Inspired by Clingfish Sucker Nanofilaments

Underwater adhesive materials are in high demand in various fields, and fish species with sucker disks have attracted attention due to their superior performance and interesting structures. The clingfish, in particular, is widely known for using hierarchical sucker disk structures to demonstrate rapid and strong adhesion to rocky surfaces under strong currents. We examined the combination of nanofilaments and mucus in the clingfish sucker disk. Nanofilaments reinforce mucus adhesion force by reducing the compliance without affecting the contact area. We prepared structures from hard polymers and soft polydimethylsiloxane (PDMS) that mimicked clingfish sucker nanofilaments and mucus, with these biomimetic structures showing significant adhesion force underwater. Furthermore, the hardness and length of the nanofilaments and Young’s modulus and thickness of the mucus-mimicking PDMS layer had critical effects on the adhesion force. According to the results, clingfish nanofilaments act as hard bracing for the soft mucus, and the structural combination of the conflicting characteristics of hardness and softness, thus achieved, is crucial for strong adhesion

A New Concept for an Adhesive Material Inspired by Clingfish Sucker Nanofilaments

Underwater adhesive materials are in high demand in various fields, and fish species with sucker disks have attracted attention due to their superior performance and interesting structures. The clingfish, in particular, is widely known for using hierarchical sucker disk structures to demonstrate rapid and strong adhesion to rocky surfaces under strong currents. We examined the combination of nanofilaments and mucus in the clingfish sucker disk. Nanofilaments reinforce mucus adhesion force by reducing the compliance without affecting the contact area. We prepared structures from hard polymers and soft polydimethylsiloxane (PDMS) that mimicked clingfish sucker nanofilaments and mucus, with these biomimetic structures showing significant adhesion force underwater. Furthermore, the hardness and length of the nanofilaments and Young’s modulus and thickness of the mucus-mimicking PDMS layer had critical effects on the adhesion force. According to the results, clingfish nanofilaments act as hard bracing for the soft mucus, and the structural combination of the conflicting characteristics of hardness and softness, thus achieved, is crucial for strong adhesion

Hydrophilic Gold Nanoparticles Adaptable for Hydrophobic Solvents

Surface ligand molecules enabling gold nanoparticles to disperse in both polar and nonpolar solvents through changes in conformation are presented. Gold nanoparticles coated with alkyl-head-capped PEG derivatives were initially well dispersed in water through exposure of the PEG residue (bent form). When chloroform was added to the aqueous solution of gold nanoparticles, the gold nanoparticles were transferred from an aqueous to a chloroform phase through exposure of the alkyl-head residue (straight form). The conformational change (bent to straight form) of immobilized ligands in response to the polarity of the solvents was supported by NMR analyses and water contact angles

Sub-100 nm Gold Nanoparticle Vesicles as a Drug Delivery Carrier enabling Rapid Drug Release upon Light Irradiation

Previously, we reported gold nanoparticles coated with semifluorinated ligands self-assembled into gold nanoparticle vesicles (AuNVs) with a sub-100 nm diameter in tetrahydrofuran (THF). Although this size is potentially useful for in vivo use, the biomedical applications of AuNVs were limited, as the vesicular structure collapsed in water. In this paper, we demonstrate that the AuNVs can be dispersed in water by cross-linking each gold nanoparticle with thiol-terminated PEG so that the cross-linked vesicles can work as a drug delivery carrier enabling light-triggered release. Rhodamine dyes or anticancer drugs were encapsulated within the cross-linked vesicles by heating to 62.5 °C. At this temperature, the gaps between nanoparticles open, as confirmed by a blue shift in the plasmon peak and the more efficient encapsulation than that observed at room temperature. The cross-linked AuNVs released encapsulated drugs upon short-term laser irradiation (5 min, 532 nm) by again opening the nanogaps between each nanoparticle in the vesicle. On the contrary, when heating the solution to 70 °C, the release speed of encapsulated dyes was much lower (more than 2 h) than that triggered by laser irradiation, indicating that cross-linked AuNVs are highly responsive to light. The vesicles were efficiently internalized into cells compared to discrete gold nanoparticles and released anticancer drugs upon laser irradiation in cells. These results indicate that cross-linked AuNVs, sub-100 nm in size, could be a new type of light-responsive drug delivery carrier applicable to the biomedical field

Influence of Hydrophobic Structures on the Plasma Membrane Permeability of Lipidlike Molecules

A series of FITC-labeled hydrophobic molecules (1−8) were prepared, and their cellular uptakes have been investigated using cell-cycle-synchronized HeLa cells. The cellular membrane permeability of compounds strongly depended on both the chemical structure and the cell-cycle phase. In the G1/S phase, branched hydrocarbon-containing 3 and cis-olefin-containing 2 and 8 were efficiently internalized into cells by passive diffusion. In contrast, linear alkyl chain-containing 1 and 7 were retained on the membrane without rapid internalization. In the M phase, rapid permeation was suppressed for all molecules

Thermopower Modulation Analyses of High-Mobility Transparent Amorphous Oxide Semiconductor Thin-Film Transistors

Transparent amorphous oxide semiconductor InSnZnOx (ITZO)-based thin-film transistors (TFTs) exhibit a high field-effect mobility (μFE). Although ITZO-TFTs have attracted increasing attention as a next-generation backplane of flat panel displays, the origin of the high μFE remains unclear due to the lack of systematic quantitative analyses using thermopower (S) as the measure. Here, we show that the high μFE originates from an extremely light carrier effective mass (m*) and a long carrier relaxation time (τ). The S measurements of several ITZO films with different carrier concentrations clarified that m* of ITZO films is ∼0.11 m0, which is ∼70% of that of a commercial oxide semiconductor, amorphous InGaZnO4 (∼0.16 m0). We then fabricated bottom-gate-top-contact ITZO-TFTs displaying excellent transistor characteristics (μFE ∼ 58 cm2 V–1 s–1) using amorphous AlOx as the gate insulator and demonstrated that the effective thickness increases with the gate voltage. This suggests that the bulk predominantly contributes to the drain current, which results in τ as long as ∼3.6 fs, which is quadruple that of amorphous InGaZnO4-TFTs (∼0.9 fs). The present results are useful to further improve the mobility of ITZO-TFTs

Thermoresponsive Assembly of Gold Nanoparticles Coated with Oligo(Ethylene Glycol) Ligands with an Alkyl Head

This paper presents the thermoresponsive assembly behaviors of gold nanoparticles (AuNPs; 3, 5, and 10 nm in diameter) that are coated with a self-assembled monolayer of oligo­(ethylene glycol) (OEG) ligands terminated with alkyl heads. AuNPs (5 nm in diameter) coated with OEG ligands without an alkyl head did not assemble within a temperature range from 20 to 70 °C. However, AuNPs coated with ethyl, iso-propyl, and propyl-headed OEG AuNPs afforded assembly at temperatures of 56, 33, and 19 °C, respectively, indicating that the assembly temperature can be tuned over a wide range by slight changes in the hydrophobicity of the alkyl head. Almost no hysteresis during the heating/cooling cycles was observed for the assembly/disassembly process. The diameter of the AuNPs also affected the assembly temperature, with increases in the diameter of the AuNP affording a lower assembly temperature. The ligand with the shorter alkyl tail length provided the lower assembly temperature of AuNPs than the ligand with longer tail