Mesoporous K-doped NiCo2O4 derived from a Prussian blue analog: high-yielding synthesis and assessment as oxygen evolution reaction catalyst.

The conversion and storage of clean renewable energy can be achieved using water splitting. However, water splitting exhibits sluggish kinetics because of the high overpotentials of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) and should therefore be promoted by OER and/or HER electrocatalysts. As the kinetic barrier of the former reaction exceeds that of the latter, high-performance OER catalysts are highly sought after. Herein, K-doped NiCo2O4 (HK-NCO) was hydrothermally prepared from a Prussian blue analog with a metal-organic framework structure and assessed as an OER catalyst. Extensive K doping increased the number of active oxygen vacancies and changed their intrinsic properties (e.g., binding energy), thus increasing conductivity. As a result, HK-NCO exhibited a Tafel slope of 49.9 mV dec-1 and a low overpotential of 292 mV at 10 mA cm-2, outperforming a commercial OER catalyst (Ir) and thus holding great promise as a component of high-performance electrode materials for metal-oxide batteries and supercapacitors.

Ultrasensitive Hypoxia Sensing at the Single-Molecule Level via Super-Resolution Quantum Dot-Linked Immunosandwich Assay.

Activated hypoxia-inducible factor-1alpha (HIF-1α) plays an important role in the adaptive response of tumor cells to oxygen changes through the transcriptional activation of genes that regulate important biological processes required for tumor survival and progression. In this study, we developed an ultrasensitive hypoxia sensor based on read-out with quantum dots on a gold nanodisc (quantum dot-linked immunosandwich assay, QLISA) with excellent selectivity for HIF-1α. The immunoassay platform was established by comparing the immune response results using Qdot525 as a detection nanoprobe instead of a fluorescent dye (Alexa488) (fluorescent-linked immunosandwich assay, FLISA). In addition, using three-dimensional total internal reflection fluorescence microscopy, the platform was optically sectioned along the z-axis at 10 nm intervals to compare the height difference between the nanodisc and the nanoprobe following the QLISA and FLISA procedures and to localize the target location. Here, the super-resolution QLISA (srQLISA)-based hypoxia sensor exhibited high accuracy and precision for the detection of HIF-1α-extracted samples in cancer spheroids compared with the super-resolution FLISA (srFLISA) method. The developed nanobiosensor method demonstrated a wide dynamic linear detection range of 32.2 zM-8.0 pM with a limit of detection of 16 zM under optimal experimental conditions for HIF-1α, an approximate 106-fold enhanced detection sensitivity compared with the conventional enzyme-linked immunosorbent assay method based on absorbance. The detection of HIF-1α using the newly developed srQLISA sensor allows for independently predicting tumor progression and early cancer onset increases in the microvasculature density of tumor lesions.

Scanning acoustic microscopy for material evaluation.

Scanning acoustic microscopy (SAM) or Acoustic Micro Imaging (AMI) is a powerful, non-destructive technique that can detect hidden defects in elastic and biological samples as well as non-transparent hard materials. By monitoring the internal features of a sample in three-dimensional integration, this technique can efficiently find physical defects such as cracks, voids, and delamination with high sensitivity. In recent years, advanced techniques such as ultrasound impedance microscopy, ultrasound speed microscopy, and scanning acoustic gigahertz microscopy have been developed for applications in industries and in the medical field to provide additional information on the internal stress, viscoelastic, and anisotropic, or nonlinear properties. X-ray, magnetic resonance, and infrared techniques are the other competitive and widely used methods. However, they have their own advantages and limitations owing to their inherent properties such as different light sources and sensors.This paper provides an overview of the principle of SAM and presents a few results to demonstrate the applications of modern acoustic imaging technology. A variety of inspection modes, such as vertical, horizontal, and diagonal cross-sections have been presented by employing the focus pathway and image reconstruction algorithm. Images have been reconstructed from the reflected echoes resulting from the change in the acoustic impedance at the interface of the material layers or defects. The results described in this paper indicate that the novel acoustic technology can expand the scope of SAM as a versatile diagnostic tool requiring less time and having a high efficiency.

Formation of high-density CuBi2O4 thin film photocathodes with polyvinylpyrrolidone-metal interaction.

We present a polymer-assisted spin coating process used to fabricate high-density p-type CuBi2O4 (CBO) thin films. Polyvinylpyrrolidone (PVP) is introduced in the precursor solutions in order to promote uniform nucleation of CBO and prevent formation of the secondary phase, such as Bi2O3, by Bi3+ ion hydrolysis. Slow PVP molecule decomposition during the two-step annealing process, with a 1 M/0.5 M (Bi3+/Cu2+) metal ion concentration, enables optimum contact at the CBO/substrate interface by avoiding formation of voids. This resulted in the formation of non-porous, compact CBO thin films. The highest current density of the photoelectrochemical (PEC) oxygen reduction reaction is obtained with non-porous, compact CBO thin films due to unimpeded charge transport through the CBO bulk, as well as across the interface. When combined with silicon, the high-density CBO thin film investigated in this work is expected to provide new PEC tandem cell options to use for solar applications.

Selective shape control of cerium oxide nanocrystals for photocatalytic and chemical sensing effect.

In this study, we report the precise shape control of crystalline cerium oxide, whose morphology changes between nanorods and nanoparticles in a short time. The proposed synthetic route of cerium oxide nanorods was highly dependent on the reaction time, and 10 min was determined to be the optimum synthetic condition. The cerium oxide nanorods were further converted into nanoparticles by the spontaneous assembly of cerium oxide nanoparticles into nanorods. The transmission electron microscopy results showed that the synthesized nanorods grew with high crystallinity along the 〈110〉 direction. The cerium oxide nanorods have been proven to be very efficient electron mediators for use as excellent photocatalytic materials and highly sensitive chemical sensors. The chemical sensor fabricated on a carbon paper substrate showed the high sensitivity of 1.81 µA mM-1 cm-2 and the detection limit of 6.4 µM with the correlation coefficient of 0.950.

One-Shot Dual-Code Immunotargeting for Ultra-Sensitive Tumor Necrosis Factor-α Nanosensors by 3D Enhanced Dark-Field Super-Resolution Microscopy.

Tumor necrosis factor-α (TNF-α) is a significant mediator of autoimmune diseases and an inflammatory protein biomarker. A novel method for the immunotargeting of TNF-α has been developed using three-dimensional (3D) enhanced dark-field super-resolution microscopy (3D EDF-SRM) based on ultrasensitive dual-code plasmonic nanosensing. Dual-code EDF-based 3D SRM improved the localization precision and sensitivity with a least-cubic algorithm, which provides accurate position information for the immunotargeted site. A dual-view device and digital single-lens reflex (DSLR) camera were used for simultaneous dual confirmable quantitative and qualitative immunoscreening based on enhanced dark-field scattering images. Two different sizes of silver nanoparticles (40- and 80-nm AgNPs) were compared to enhance the scattering signal of the immunotargeted plasmonic nanoprobe for the 3D EDF-SRM system. The standard TNF-α was immunotargeted at a single-molecule level and was quantitatively analyzed by measuring the scattering signals of 80 nm AgNPs on an array chip with gold-nanostages (GNSs) with 100 nm spot diameters. The localization precision in the 80 nm AgNP immunotag on the GNS narrowed to ∼9.5 nm after applying the least-cubic algorithm. The developed nanosensor exhibited a detection limit of 65 zM (1.14 ag/mL; S/N = 3) with a wide dynamic detection range of 65 zM-2.08 pM (1.14 ag/mL-36.4 pg/mL; R = 0.9921). These values are 20-33 400 000 times lower than detection limits obtained using previous methods. In addition, a recovery greater than 98% was achieved by spiking standard TNF-α into human serum samples. This method should facilitate simultaneous improvements in immunotargeting precision and ultrahigh sensitive detection of various disease-related target protein molecules at a single-molecule level.

Analysis of dural sac thickness in the human cervical spine.

The thickness of the dura mater in the human cervical spine can vary between individuals and by vertebral level; these differences can result in various clinical outcomes. The purpose was to measure and analyze cervical dura mater thickness. Microscopic measurements were made of tissue from human cadavers. The subjects were nine human cadavers with no previous history of spinal deformity or surgery. Fourteen segments of both anterior and posterior dura mater from the C1 to C7 cervical vertebrae were obtained. Dura mater thickness was measured using an infrared laser-based confocal microscope. Statistical analyses were performed to examine the relationships of cervical dura mater thickness with vertebral level, age, and sex. The overall average cervical dura mater thickness was 379.3 × 10-3 mm. Statistically significant differences in thickness were found between the anterior and posterior segments (P < 0.0001). Moreover, the thickness at each vertebral level was significantly different from the thicknesses at the other levels (P < 0.05). The posterior dura mater thickness was highest at C1 and lowest at C5/6. Posterior dura mater thickness was significantly different at the axial, sub-axial, and lower cervical levels, whereas anterior dura mater thickness was relatively constant among levels. A significant correlation was found between thickness and age (P < 0.05); however, the average dura mater thickness was not significantly different between males and females. This study shows anatomical differences in cervical dura mater thickness with respect to vertebral level and age. These results provide anatomical information that will inform basic research and clinical approaches.

Enhanced detection sensitivity of carcinoembryonic antigen on a plasmonic nanoimmunosensor by transmission grating-based total internal reflection scattering microscopy.

Carcinoembryonic antigen (CEA) is a glycoprotein associated with colorectal carcinomas and is commonly used as a clinical tumor marker. Enhanced detection sensitivity for the assay of CEA molecules was achieved on a plasmonic nanoimmunosensor by wavelength-dependent transmission grating (TG)-based total internal reflection scattering microscopy (TIRSM). The plasmonic nanoparticles were placed in an evanescent field layer on a glass nanoimmunosensor that produced evanescent wave scattering by the total internal reflection of light from two lasers. The light scattered by target protein (CEA)-bound 20-nm silver nanoparticles (plasmonic nanoprobes) was collected and spectrally isolated in first-order spectral images (n=+1) by a TG (70 grooves/mm). The combination of evanescent wave scattering and TG ​significantly enhanced the detection sensitivity and selectivity due to the minimized spectroscopic interference and background noise. The TG-TIRSM method detected the CEA molecules at concentrations down to 19.75zM with a wide linear dynamic range of 19.75zM-39.50nM (correlation coefficient, R=0.9903), which was 45 to 1.25×109 times lower than the detection limits and 2×105 to 2×1011 times wider than the dynamic ranges of previous assay methods. In particular, by simply changing the antibody of the target molecule, this technique can be used to detect various disease-related protein biomarkers directly in human biological samples at the single-molecule level.

Ultrasensitive Detection of α-Fetoprotein by Total Internal Reflection Scattering-Based Super-Resolution Microscopy for Superlocalization of Nano-Immunoplasmonics.

Superlocalization of immunoplasmonic nanotags on antibody-bound gold-nanoislands (GNIs) along the x and y coordinates was determined using total internal reflection scattering-based super-resolution microscopy (TIRS-SRM) at subdiffraction limit resolution. Individual immunoplasmonic nanotags (20 nm silver nanoparticles) and 100 nm GNIs were selectively acquired in the evanescent field layer by wavelength-dependent plasmonic scattering using two illumination lasers (405 and 635 nm, respectively). α-Fetoprotein (AFP), a liver cancer-related model protein, was immobilized as a target molecule on the GNI arrays. The centroid position of a localized immunoplasmonic nanotag on the GNI was resolved at less than 10 nm of spatial resolution by applying 2D Gaussian fitting to its point spread function. This method showed enhanced sensitive quantification with a limit of detection (LOD) of 7.04 zM (1-2 molecules of AFP/GNI), which was 100-5000000000 times lower than detection limits obtained with previous AFP detection methods. Furthermore, the method was also successfully applied to quantify AFP molecules at the single-molecule level in human serum samples. The wavelength-dependent TIRS-SRM method was demonstrated to be an effective tool for superlocalizing individual protein molecules and interactions in nanoscale regions and was a reliable method for the ultrasensitive quantitative detection of disease-related protein molecules as a nanosensor and for diagnosis at the single-molecule level.

Quantitative nanoimmunosensor based on dark-field illumination with enhanced sensitivity and on-off switching using scattering signals.

A nanoimmunosensor based on wavelength-dependent dark-field illumination with enhanced sensitivity was used to detect a disease-related protein molecule at zeptomolar (zM) concentrations. The assay platform of 100-nm gold nanospots could be selectively acquired using the wavelength-dependence of enhanced scattering signals from antibody-conjugated plasmonic silver nanoparticles (NPs) with on-off switching using optical filters. Detection of human thyroid-stimulating hormone (hTSH) at a sensitivity of 100 zM, which corresponds to 1-2 molecules per gold spot, was possible within a linear range of 100 zM-100 fM (R=0.9968). A significantly enhanced sensitivity (~4-fold) was achieved with enhanced dark-field illumination compared to using a total internal reflection fluorescence immunosensor. Immunoreactions were confirmed via optical axial-slicing based on the spectral characteristics of two plasmonic NPs. This method of using wavelength-dependent dark-field illumination had an enhanced sensitivity and a wide, linear dynamic range of 100 zM-100 fM, and was an effective tool for quantitatively detecting a single molecule on a nanobiochip for molecular diagnostics.

Super-resolution of fluorescence-free plasmonic nanoparticles using enhanced dark-field illumination based on wavelength-modulation.

Super-resolution imaging of fluorescence-free plasmonic nanoparticles (NPs) was achieved using enhanced dark-field (EDF) illumination based on wavelength-modulation. Indistinguishable adjacent EDF images of 103-nm gold nanoparticles (GNPs), 40-nm gold nanorods (GNRs), and 80-nm silver nanoparticles (SNPs) were modulated at their wavelengths of specific localized surface plasmon scattering. The coordinates (x, y) of each NP were resolved by fitting their point spread functions with a two-dimensional Gaussian. The measured localization precisions of GNPs, GNRs, and SNPs were 2.5 nm, 5.0 nm, and 2.9 nm, respectively. From the resolved coordinates of NPs and the corresponding localization precisions, super-resolution images were reconstructed. Depending on the spontaneous polarization of GNR scattering, the orientation angle of GNRs in two-dimensions was resolved and provided more elaborate localization information. This novel fluorescence-free super-resolution method was applied to live HeLa cells to resolve NPs and provided remarkable sub-diffraction limit images.

Plasmonic metal scattering immunoassay by total internal reflection scattering microscopy with nanoscale lateral resolution.

Immunoassays on nanopatterned chips through TIRS detection based on reconstructing the three dimensional position provided a nanoscale accuracy of the lateral resolution by using the z-stage controller in the spatial range up to 10 nm. This method offers highly accurate and sensitive quantification with the zeptomolar (∼10(-21) M) detection of proteins.

Growth Mechanism of Highly Crystalline CdS Spheres with Grainy Surfaces.

Owing to its excellent optical and electronic properties, CdS has increasingly received considerable attention as a promising III-V semiconductor material. We report on the growth mechanism of CdS spheres with high crystallinity, uniform size distribution, and grainy surfaces under hydrothermal conditions. By controlling the reaction time, temperature, and pH, CdS with various morphologies and size distributions could be synthesized. The analysis of the time evolution of the morphology and size of the CdS particles provided good indications on the growth mechanism. In addition, the effects of the temperature and pH on the formation and size of the CdS spherical particles were studied to understand the reaction mechanism. The characterization of the physicochemical properties of the synthesized samples by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and Raman spectroscopy is presented.

Quantitative compositional profiling of conjugated quantum dots with single atomic layer depth resolution via time-of-flight medium-energy ion scattering spectroscopy.

We report the quantitative compositional profiling of 3-5 nm CdSe/ZnS quantum dots (QDs) conjugated with a perfluorooctanethiol (PFOT) layer using the newly developed time-of-flight (TOF) medium-energy ion scattering (MEIS) spectroscopy with single atomic layer resolution. The collection efficiency of TOF-MEIS is 3 orders of magnitude higher than that of conventional MEIS, enabling the analysis of nanostructured materials with minimized ion beam damage and without ion neutralization problems. The spectra were analyzed using PowerMEIS ion scattering simulation software to allow a wide acceptance angle. Thus, the composition and core-shell structure of the CdSe cores and ZnS shells were determined with a 3% composition uncertainty and a 0.2-nm depth resolution. The number of conjugated PFOT molecules per QD was also quantified. The size and composition of the QDs were consistent with those obtained from high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, respectively. We suggest TOF-MEIS as a nanoanalysis technique to successfully elucidate the core-shell and conjugated layer structures of QDs, which is critical for the practical application of QDs in various nano- and biotechnologies.

Shape control of magnesium oxysulfate granules using an ethanolamine chelate.

Shape control of inorganic nanomaterials during hydrothermal syntheses is crucial for fine-tuning the function of these materials, which are widely utilized in semiconductors, ceramics, and optical devices. In particular, magnesium compounds possess many desirable physical properties such as high thermal stability, wide band gap and high secondary electron emission yield, which allow their application as polymeric resins, cements, reinforcements, and fillers. However, conventional synthetic methods often require extreme reaction conditions such as high temperatures, high pressures, or prolonged reaction times. Additionally, various shape control methods are typically quite complicated and time consuming under conventional parameters. In this work, magnesium oxysulfate (5Mg(OH)2 x MgSO4 x 3H2O) granules of various shapes were fabricated by introducing ethanolamine chelate during hydrothermal reaction at a relatively low temperature and pressure. The strong interaction between ethanolamine and Mg2+ produced 5Mg(OH)2 x MgSO4 x 3H2O granules in the form of flakes, flowers, or whiskers through self-assembly this formation is dependent on concentration, reaction time, and temperature. The physicochemical properties of the samples were investigated using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis.

Facile fabrication of a cerium oxide nanorod.

Nanorods are one-dimensional structures that possess interesting physical and electrical properties and have potential applications in various areas. Cerium oxide, a very abundant rare earth element, is widely utilized in catalysts of exhaust systems, chemical abrasives, electrical devices, oxidant semiconductor devices, UV adsorbents, and fluorescence emitting materials. Shape control is important for controlling the overall shape and quality of the nanorod during synthesis. However, most of the shape control studies of cerium oxide nanomaterials in the literature have been performed under high temperature and high pressure conditions, which impede industrial mass production. In this study, we describe a facile synthesis method for producing Ce(OH)3 nanorods with different diameters through the application of the common ion effect principle using NH+, Cl-, and OH- ions. The resulting Ce(OH)3 rods were dried to produce the corresponding cerium oxide products. Consequently, a one-pot reaction under mild conditions allowed for the production of high-quality nanorods after much shorter reaction times, with the additional natural release of counter ions under reaction equilibrium. The shape and physicochemical properties were characterized using various analytical methods, including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and Raman spectroscopy.

Growth mechanism of cubic MgO granule via common ion effect.

MgO is a typical wide bandgap insulator with its excellent thermodynamic stability, low dielectric constant, and low refractive index for growing various thin film materials. For this application, it is worth developing and understanding suitable growth method for MgO nanostructure. In this study, cubic MgCO3 have been successfully prepared via hydrolysis control of magnesium salt and alkaline solution with common ions to form nanoflake assembly. An optimum hydrothermal process and its shape evolution of cubic MgCO3 and MgO granules are analyzed. The physicochemical properties of the obtained samples are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier Transform InfraRed (FT-IR) to show high purity and structural uniformity of magnesium compounds.

Extraction of three-dimensional information of biological membranous tissue with scanning confocal infrared laser microscope tomography.

The "LEXT" confocal laser scanning microscope has been used for the three-dimensional (3D) imaging of the surface of specimens, especially in materials science fields, by the penetration of near-infrared (NIR) light without mechanical cutting, deposition, or other specimen pretreatment. Noninvasive investigation of various biological tissues such as human spinal dura mater, rat aorta, and cornea without the dehydration process was successfully carried out with the "LEXT," in order to access both surface and internal topographic images of the biological structures at a good status of the wet tissue such as in vivo, especially in measuring tissue thickness. The confocal NIR laser microscopy offers the viable means to visualize tissue architecture and its thickness in microdomain to integrate 3D images efficiently. We believe that the "LEXT" has a good application for biological researchers to study biomaterials, and it would be useful as a diagnostic tool in the near future.

Selective fluorescent-free detection of biomolecules on nanobiochips by wavelength dependent-enhanced dark field illumination.

Individual silver nanoparticle-conjugated target protein (cTnI) molecules on gold-nanopatterned chip were selectively detected by wavelength dependent-enhanced dark field illumination. Using specific nanoparticles with unique sizes and materials, the immunotargeted nanoparticle on the chips was detected at the single-molecule level by monitoring changes in the plasmonic resonance based on wavelength dependence.

In situ control of oxygen vacancies in TiO2 by atomic layer deposition for resistive switching devices.

Oxygen vacancies (V(O)) have profound effects on the physical and chemical performance of devices based on oxide materials. This is particularly true in the case of oxide-based resistive random access memories, in which memory switching operation under an external electrical stimulus is closely associated with the migration and ordering of the oxygen vacancies in the oxide material. In this paper, we report on a reliable approach to in situ control of the oxygen vacancies in TiOx films. Our strategy for tight control of the oxygen vacancy is based on the utilization of plasma-enhanced atomic layer deposition of titanium oxide under precisely regulated decomposition of the precursor molecules (titanium (IV) tetraisopropoxide, Ti[OCH(CH3)2]4) by plasma-activated reactant mixture (N2+O2). From the various spectroscopic and microstructural analyses by using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, confocal Raman spectroscopy, and spectroscopic ellipsometry, we found that the precursor decomposition power (R(F)) of plasma-activated reactant mixture determines not only the oxygen vacancy concentration but also the crystallinity of the resulting TiO(x) film: nanocrystalline anatase TiO(x) with fewer oxygen vacancies under high R(F), while amorphous TiOx with more oxygen vacancies under low RF. Enabled by our controlling capability over the oxygen vacancy concentration, we were able to thoroughly elucidate the effect of oxygen vacancies on the resistive switching behavior of TiO(x)-based memory capacitors (Pt/TiO(x)/Pt). The electrical conduction behavior at the high resistance state could be explained within the framework of the trap-controlled space-charge-limited conduction with two characteristic transition voltages. One is the voltage (V(SCL)) for the transition from Ohmic conduction to space-charge-limited conduction, and the other is the voltage (V(TFL)) for transition from space-charge-limited conduction to trap-filled-limited conduction. In this work, we have disclosed for the first time the dependence of these two characteristic transition voltages (i.e., V(SCL) and V(TFL)) on the oxygen vacancy concentration.