Real-time morphological detection of label-free submicron-sized plastics using flow-channeled differential interference contrast microscopy.

Owing to the surge in plastic waste generated during the COVID-19 pandemic, concerns regarding microplastic pollution in aqueous environments are increasing. Since microplastics (MPs) are broken down into submicron (< 1 µm) and nanoscale plastics, their real-time morphological detection in water is necessary. However, the decrease in the scattering cross-section of MPs in aqueous media precludes morphological detection by bright-field microscopy. To address this problem, we propose and demonstrate a differential interference contrast (DIC) system that incorporates a magnification-enhancing system to detect MPs in aqueous samples. To detect MPs in both the stationary and mobile phases, a microfluidic chip was designed, taking into consideration the imaging depth of focus and flow resistance. MPs of various sizes flowing in deionized, tap, and pond water at varying speeds were observed under Static and Flow conditions. Successful real-time morphological detection and quantification of polystyrene beads down to 200 nm at a constant flow rate in water were achieved. Thus, the proposed novel method can significantly reduce analysis time and improve the size-detection limit. The proposed DIC microscopy system can be coupled with Raman or infrared spectroscopy in future studies for chemical composition analysis. ENVIRONMENTAL IMPLICATION: Microplastics (MPs), particularly submicron plastics < 1-µm, can pose a risk to human health and aquatic ecosystems. Existing methods for detecting MPs in the aqueous phase have several limitations, including the use of expensive instruments and prolonged and labor-intensive procedures. Our results clearly demonstrated that a new low-cost flow-channeled differential interference contrast microscopy enables the real-time morphological detection and quantification of MPs down to 200 nm under flowing conditions without sample labeling. Consequently, our proposed rapid method for accurate quantitative measurements can serve as a valuable reference for detecting submicron plastics in water samples.

Eye-Mimicked Neural Network Composed of Photosensitive Neural Spheroids with Human Opsin Proteins.

An in vitro model, composed of the short-wavelength human opsins and rhodopsins, is created. Two types of photosensitive neural spheroids are transfected for selective reaction under bluish-purple and green lights. These are employed to two devices with intact neuron and neural-spheroid to study the interaction. By photostimulation, the photosensitive spheroid initiated photoactivation, and the signal generated from its body is transmitted to adjacent neural networks. Specifically, the signal traveled through the axon bundle in narrow gap from photosensitive spheroid to intact spheroid as an eye-to-brain model including optic nerve. The whole process with photosensitive spheroid is monitored by calcium ion detecting fluorescence images. The results of this study can be applied to examine vision restoration and novel photosensitive biological systems with spectral sensitivity.

Photosensitive Nanodiscs Composed of Human Photoreceptors for Refractive Index Modulation at Selective Wavelengths.

A photoreceptor on the retina acts as an optical waveguide to transfer an individual photonic signal to the cell inside, which is determined by the refractive index of internal materials. Under the photoactivation of photoreceptors making conformational and chemical variation in a visual cell, the optical signal modulation is demonstrated using an artificial photoreceptor-based waveguide with a controlling beam refraction. Two types of nanodiscs are made of human photoreceptor proteins, short-wavelength-sensitive opsin and rhodopsin, with spectral sensitivity. The refractive index and nonlinear features of those two photosensitive nanodiscs are investigated as fundamental properties. The photonanodiscs are photoactivated in such a way that allow refractive index tuning over 0.18 according to the biological function of the respective proteins with color-dependent response.

Multifunctional Additives for High-Energy-Density Lithium-Ion Batteries: Improved Conductive Additive/Binder Networks and Enhanced Electrochemical Properties.

Cylindrical-type cells have been widely adopted by major battery and electric vehicle manufacturers owing to their price competitiveness, safety, and easy expandability. However, placement of electrodes at the core of cylindrical cells is currently restricted because of high electrode curvature and the lack of specialized electrodes and electrode materials. Here, we report the realization of highly flexible high-energy-density electrodes (active material loading of >98.4%) that can be used at the cores of cylindrical cells. The improved properties result from the introduction of a multifunctional poly(melamine-co-formaldehyde) (MF copolymer) additive, which yields a relatively more fluidic and well-dispersed slurry using only 0.08 wt %. MF copolymer-mediated formation of completely wrapped CNT/PVDF networks on LiCoO2 (LCO) and accompanying contact enhancement between LCO and carbon nanotubes (CNTs) resulted in an increase of electrical and mechanical properties of the two types (composites with or without collectors) of electrodes compared with those of additive-free electrodes. Flexibility tests were carried out by rolling electrodes onto cylinder substrates (diameters of ca. 1 and 10 mm); this process resulted in relatively lower resistance changes of the MF copolymer-containing electrodes than for the reference electrodes. In addition, capacity retention after 100 cycles for cells with and without MF copolymers was approximately 10-20% better for the samples with the MF copolymer than for those without. CNT/PVDF networks with MF copolymers were proven to induce a relatively thin and stable cathode electrolyte interface layer accompanying the chemical bond formation during cycling.

Electrically focus-tuneable ultrathin lens for high-resolution square subpixels.

Owing to the tremendous demands for high-resolution pixel-scale thin lenses in displays, we developed a graphene-based ultrathin square subpixel lens (USSL) capable of electrically tuneable focusing (ETF) with a performance competitive with that of a typical mechanical refractive lens. The fringe field due to a voltage bias in the graphene proves that our ETF-USSL can focus light onto a single point regardless of the wavelength of the visible light-by controlling the carriers at the Dirac point using radially patterned graphene layers, the focal length of the planar structure can be adjusted without changing the curvature or position of the lens. A high focusing efficiency of over 60% at a visible wavelength of 405 nm was achieved with a lens thickness of <13 nm, and a change of 19.42% in the focal length with a 9% increase in transmission was exhibited under a driving voltage. This design is first presented as an ETF-USSL that can be controlled in pixel units of flat panel displays for visible light. It can be easily applied as an add-on to high resolution, slim displays and provides a new direction for the application of multifunctional autostereoscopic displays.

Three-dimensional, millimeter-scale semiconducting SWCNT aerogels for highly sensitive ozone detection.

Semiconducting frameworks possessing porous structure are promising platforms for the detection of hazardous gas molecules. In this study, we propose a facile route to fabricate millimeter-scale, three-dimensional semiconducting SWCNT (s-SWCNT) aerogels and demonstrate deactivation of the co-existing metallic SWCNT (m-SWCNT) network via electrical breakdown process. In particular, the on-off ratio of the modulated semiconducting aerogel after the electrical breakdown process was 205, which is an increase of 18.9 times over that before the process. The modulated semiconducting SWCNT aerogels with a large specific surface area (∼1270 m2 g-1) demonstrated their applicability for highly sensitive ppb-level ozone detection. The modulated semiconducting networks led to a 1310 % increase in the magnitude of response to 30-ppb ozone gas injection compared with that of pristine SWCNT aerogels. Furthermore, the prepared aerogels could detect 3 ppb of ozone within 40 s and retain stable reversible ozone detection for 200 cyclic operations over 100 h. Thus, the proposed semiconducting SWCNT aerogels are a promising candidate for highly sensitive environmental gas sensors.

Three-Dimensional Monolithic Organic Battery Electrodes.

Design of freestanding electrodes incorporated with redox-active organic materials has been limited by the poor intrinsic electrical conductivity and lack of methodology driving the feasible integration of conductive substrate and the organic molecules. Single-walled carbon nanotube (SWCNT) aerogels, which possess continuous network structure and high surface area, offer a three-dimensional electrically conducting scaffold. Here, we fabricate monolithic organic electrodes by coating a nanometer-scale imide-based network (IBN) that possesses abundant redox-active sites on the 3D SWCNT scaffold. The substantially integrated 3D monolithic organic electrodes sustain high electrical conductance through a 3D electronic pathway in their compressed form (∼21 µm). A thin and controllable layer (<8 nm) of IBN organic materials has a strong adhesion onto the ultra-lightweight and conductive substrate and facilitates multielectron redox reactions to deliver a specific capacity of up to 1550 mA h g-1 (corresponding to the areal capacity of ∼2.8 mA h cm-2). The redox-active IBN in synergy with the 3D SWCNT scaffold can enable superior electrochemical performances compared to the previously reported organic-based electrode architectures and inorganic-based electrodes.

Determination of the molecular assembly of actin and actin-binding proteins using photoluminescence.

Actin, the most abundant protein in cells, polymerizes into filaments that play key roles in many cellular dynamics. To understand cell dynamics and functions, it is essential to examine the cytoskeleton structure organized by actin and actin-binding proteins. Here, we pave the way for determining the molecular assembly of the actin cytoskeleton using direct photonic in situ analysis, providing the photoluminescence characteristics of actin as a function of filament length and bundling, without labeling. In experiments for monomeric and filamentous actin reconstituted in vitro, structural forms of actin are identified from the peak positions and intensities of photoluminescence. Actin monomers exhibited small intensity emission peaks at 334 nm, whereas filamentous and bundled actin showed a shifted peak at 323 nm with higher intensity. The peak shift was found to be proportional to the length of the actin filament. With probing structural change of actin in various cells in vivo, our study provides an efficient and precise analytical in situ tool to examine the cytoskeleton structure. It will be beneficial for elucidating the mechanism of various cellular functions such as cell migration, differentiation, cytokinesis and adhesion. Furthermore, our technique can be applied to detect the alterations in the cell cytoskeleton that can occur during many pathological processes.

Artificial Rod and Cone Photoreceptors with Human-Like Spectral Sensitivities.

Photosensitive materials contain biologically engineered elements and are constructed using delicate techniques, with special attention devoted to efficiency, stability, and biocompatibility. However, to date, no photosensitive material has been developed to replace damaged visual-systems to detect light and transmit the signal to a neuron in the human body. In the current study, artificial nanovesicle-based photosensitive materials are observed to possess the characteristics of photoreceptors similar to the human eye. The materials exhibit considerably effective spectral characteristics according to each pigment. Four photoreceptors originating from the human eye with color-distinguishability are produced in human embryonic kidney (HEK)-293 cells and partially purified in the form of nanovesicles. Under various wavelengths of visible light, electrochemical measurements are performed to analyze the physiological behavior and kinetics of the photoreceptors, with graphene, performing as an electrode, playing an important role in the lipid bilayer deposition and oxygen reduction processes. Four nanovesicles with different photoreceptors, namely, rhodopsin (Rho), short-, medium-, and longwave sensitive opsin 1 (1SW, 1MW, 1LW), show remarkable color-dependent characteristics, consistent with those of natural human retina. With four different light-emitting diodes for functional verification, the photoreceptors embedded in nanovesicles show remarkably specific color sensitivity. This study demonstrates the potential applications of light-activated platforms in biological optoelectronic industries.

Hydrothermal Synthesis of Composition- and Morphology-Tunable Polyimide-Based Microparticles.

Polyimide is one of the most important high-performance polymers, which is widely used due to its excellent mechanical performance and thermal stability. Unlike the conventional synthetic approach, hydrothermal polymerization enables the synthesis of polyimides without any toxic solvent and catalyst. Herein, we report the synthesis of polyimide-based microparticles (PIMs) through one-pot hydrothermal polymerization using precursors of mellitic acid (MA) and three isomers of phenylenediamine (PDA) (o-, m-, and p-PDA). Interestingly, the chemical composition of PIMs was highly tunable with the choice of the PDA isomers, leading to considerable morphological differences between PIMs. The molecular dynamics simulation and density functional theory calculation of the polymeric segment of the respective PIMs suggested that the relative ratio of amide to imide influenced the rotational freedom of the polymeric chains and number of hydrogen bonds, resulting in the well-defined structures of respective PIMs. Considering the highly tunable nature of PIMs coupled with the facile synthetic protocol, we anticipate prospective potentials of PIMs in materials, energy, and composite applications.

Facile approach to synthesize highly fluorescent multicolor emissive carbon dots via surface functionalization for cellular imaging.

Luminescent nanomaterials are encouraging scaffolds for diverse applications such as chemical sensors and biosensors, imaging, drug delivery, diagnostics, catalysis, energy, photonics, medicine, and so on. Carbon dots (CDs) are a new class of luminescent carbonaceous nanomaterial that have appeared recently and reaped tremendous scientific interest. Herein, we have exploited a simple approach to prepare tuneable and highly fluorescent CDs via surface functionalization. The successful synthesis of CDs is manifested from several investigations like high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The CDs exhibit excellent water solubility and with increasing nitrogen content fluorescence quantum yield increases whereas cell toxicity decreases. The CD synthesized at high temperature (180 °C) shows very high quantum yield (more than 56%). The tuneable optical properties of CDs are systematically studied using UV-vis and fluorescence spectroscopy. The cell viability evaluation and in vitro imaging study reveals that the synthesized CDs can be employed as a potential fluorescent probe for bio-imaging without further modification.

Carrier scattering in quasi-free standing graphene on hexagonal boron nitride.

Graphene, a two-dimensional material with a honeycomb lattice, has been promoted as a next generation material because of its ultrafast charge carriers and superior electrical properties. Hexagonal boron nitride (h-BN) is an insulator explored as an ideal substrate for graphene with lattice-matching. Using raido-frequency (RF) transmission measurement which provides specific characteristics of carrier scattering in a device, we profoundly investigated the electrical properties of quasi-free standing graphene on h-BN. RF devices with graphene supported and encapsulated with h-BN were fabricated to analyze the RF signal at low temperatures from 100 to 300 K. We demonstrated the carrier behavior in graphene with thermally excited carriers and acoustic photon scattering according to heat energy. Both h-BN supported and encapsulated graphene showed a significant enhancement in RF transmission, which is close to a gold interconnector. Our device with graphene on h-BN exhibited concealed nonlinear characteristics at a specific temperature of 180 K due to the internal effects of acoustic phonon scattering, while a usual device with graphene on SiO2/Si provided a linear variation. To anticipate the potential for electronic applications, the electrical circuit properties such as impedance, resistance, and inductance were extracted from the results of RF measurement.

A Reduced Graphene Oxide Based Radio Frequency Glucose Sensing Device Using Multi-Dimensional Parameters.

A reduced graphene oxide (RGO) based glucose sensor using a radio frequency (RF) signal is demonstrated. An RGO with outstanding electrical property was employed as the interconnector material between signal electrodes in an RF electric circuit, and it was functionalized with phenylbutyric acid (PBA) as a linker molecule to bind glucoses. By adding glucose solution, the fabricated sensor with RGO and PBA showed detecting characteristics in RF signal transmission and reflection. Frequency dependent electrical parameters such as resistance, inductance, shunt conductance and shunt capacitance were extracted from the RF results under the equivalent circuit model. These parameters also provided sensing characteristics of glucose with different concentrations. Using these multi-dimensional parameters, the RF sensor device detected glucose levels in the range of 1⁻4 mM, which ordinarily covers the testing range for diabetes or medical examination. The RGO based RF sensor, which fits well to a linear curve with fine stability, holds considerable promise for biomaterials detection, including glucose.

Enhanced nonlinear optical characteristics of copper-ion-doped double crossover DNAs.

The modification of deoxyribonucleic acid (DNA) samples by sequencing the order of bases and doping copper ions opens the possibility for the design of novel nanomaterials exhibiting large optical nonlinearity. We investigated the nonlinear characteristics of copper-ion doped double crossover DNA samples for the first time to the best of our knowledge by using Z-scan and four-wave mixing methods. To accelerate the nonlinear characteristics, we prepared two types of unique DNA nanostructures composed of 148 base pairs doped with copper ions with a facile annealing method. The outstanding third-order nonlinear optical susceptibility of the copper-ion-doped DNA solution, 1.19 × 10(-12) esu, was estimated by the conventional Z-scan measurement, whereas the four-wave mixing experiment was also investigated. In the visible spectral range, the copper-ion-doped DNA solution samples provided competent four-wave mixing signals with a remarkable conversion efficiency of -4.15 dB for the converted signal at 627 nm. The interactions between DNA and copper ions contribute to the enhancement of nonlinearity due to structural and functional changes. The present study signifies that the copper-ion-doped double crossover DNA is a potential candidate as a highly efficient novel material for further nonlinear optical applications.

Broadband supercontinuum generation using a hollow optical fiber filled with copper-ion-modified DNA.

We experimentally demonstrated supercontinuum generation through a hollow core photonic bandgap fiber (HC-PBGF) filled with DNA nanocrystals modified by copper ions in a solution. Both double-crossover nano DNA structure and copper-ion-modified structure provided a sufficiently high optical nonlinearity within a short length of hollow optical fiber. Adding a higher concentration of copper ion into the DNA nanocrystals, the bandwidth of supercontinuum output was monotonically increased. Finally, we achieved the bandwidth expansion of about 1000 nm to be sufficient for broadband multi-spectrum applications.

Suprapapillary versus transpapillary stent placement for malignant biliary obstruction: which is better?

PURPOSE: To compare the complications, stent patency, and patient survival with self-expandable metal stents (SEMSs) placed above or across the sphincter of Oddi in malignant biliary obstruction. MATERIALS AND METHODS: From January 2008 to December 2012, 155 patients were treated with percutaneous transhepatic SEMS placement. Seventy-four patients underwent suprapapillary stent placement (group A), and 81 patients underwent transpapillary stent placement (group B). Complications rates, stent patency, and patient survival were evaluated and analyzed for potential predictors. RESULTS: In group A, 68 covered and 28 uncovered SEMSs were placed, and, in group B, 78 covered and 19 uncovered SEMSs were placed. Thirty-six stent-related early complications were observed in a total of 154 patients (23.4%): pancreatitis (n = 23), cholangitis (n = 12), and cholecystitis (n = 1). The early complication rates for groups A and B were 14.9% (11 of 74) and 31.3% (25 of 80), respectively (P = .016). Pancreatitis occurred in three patients (4.1%) in group A and 20 patients (25.0%) in group B (P = .001). Stent location was a single independent predictor of pancreatitis (P < .001). Stent occlusions by tumor growth was more frequently observed in group A than in group B (P = .007), whereas stent occlusion by sludge incrustation was more frequently found in group B than in group A (P = .007). There was no significant difference in cumulative stent patency (P = .401) or patient survival (P = .792) between groups. CONCLUSIONS: To decrease the incidence of pancreatitis, suprapapillary placement of SEMSs is recommended for malignant biliary obstruction, but not in the lower 2 cm of the common bile duct.

Highly tunable interfacial adhesion of glass fiber by hybrid multilayers of graphene oxide and aramid nanofiber.

The performance of fiber-reinforced composites is governed not only by the nature of each individual component comprising the composite but also by the interfacial properties between the fiber and the matrix. We present a novel layer-by-layer (LbL) assembly for the surface modification of a glass fiber to enhance the interfacial properties between the glass fiber and the epoxy matrix. Solution-processable graphene oxide (GO) and an aramid nanofiber (ANF) were employed as active components for the LbL assembly onto the glass fiber, owing to their abundant functional groups and mechanical properties. We found that the interfacial properties of the glass fibers uniformly coated with GO and ANF multilayers, such as surface free energy and interfacial shear strength, were improved by 23.6% and 39.2%, respectively, compared with those of the bare glass fiber. In addition, the interfacial adhesion interactions between the glass fiber and the epoxy matrix were highly tunable simply by changing the composition and the architecture of layers, taking advantage of the versatility of the LbL assembly.

Surface roughness effects on the frequency tuning performance of a nanoelectromechanical resonator.

Electrothermal heating is one of radio frequency tuning method in nanoelectromechanical resonators with magnetomotive transduction. This study confirmed that the surface roughness of the nanoresonator affects the electrothermal tuning performance under moderate conditions at room temperature. The effect of surface roughness on electrothermal tuning is complicated and involves interactions of mechanical and electrical properties. In addition, the electrothermal damping varied depending on the nanoscale molecular solid structure. These factors affect the signal-to-noise ratio, the effective stress of the beam, and the quality Q-factor of the nanoresonator.

Controlling the luminescence emission from palladium grafted graphene oxide thin films via reduction.

The role of palladium (Pd) in the reduction of graphene oxide (GO) thin films was investigated using a Pd assisted grafting technique. The structural and optical characteristics of these thin films were obtained from various spectroscopic analyses, which confirmed increased C[double bond, length as m-dash]C-C aromatic ring vibration and oxidation of Pd with Ar annealing. In Pd free GO, annealing of films resulted in restoration of sp(2) clusters; however, Pd grafting with non-annealed film enhanced the possibility of restoration and further annealing dramatically increased the restoration rate with enhanced blue photoluminescence (PL) emission. The blue PL emission originates from sp(2) cluster sites and the yellow-green PL from defect trapped states. As reduction of GO increased, yellow-green emission decreased and blue PL became the prominent emission. These experimental findings open up a new feasible pathway for controlling the luminescence emission from graphene oxide that furthers the technological advancement of graphene based optoelectronic devices.