Zein-Induced Polyelectrolyte Complexes for Encapsulating Triterpenoid Phytochemicals.

The hydrophobicity and aggregation of zein, a biopolymer, limit its application as an effective drug delivery carrier. Here, we developed a zein-induced polyelectrolyte (ZiP) complex and investigated its efficiency in delivering 1% hydrolyzed ginseng saponin, a compound K-rich fraction derived from the root of Panax ginseng. The ZiP complex was formulated by incorporating the self-assembled amphiphilic prolamin zein into the aqueous phase. The physical properties, encapsulation efficiency, and stability of the encapsulation system at room temperature (25 °C) and 45 °C were assessed. The effects of different ratios of zein, pullulan, and pectin on the formation of the ZiP complex, the encapsulation stability, and the cellular efficacy of ZiP complexes were also assessed. The ZiP complex was surface-modified with hydrophilic pullulan and pectin polysaccharides in a mass ratio of 1:2:0.2 through electrostatic interactions. The primary hydrophilic modification of the ZiP complex was formed by the adsorption of pullulan, which enhanced the encapsulation stability. The outermost hydrophilic layer comprised the gelling polysaccharide pectin, which further improved the stability of the macro-sized oil-encapsulated complex, reaching sizes over 50 µm. The size of the ZiP complex increased when the concentration of pectin or the total content of the ZiP complex increased to 2:4:0.2. Compound K was successfully encapsulated with a particle size of 294.8 nm and an encapsulation efficiency of 99.6%. The ZiP complex demonstrated stability at high temperatures and long-term stability of the encapsulated saponin over 24 weeks. These results revealed the potency of ZiP complexes that enhance the in vivo absorption of phytochemicals as effective drug delivery carriers that can overcome the limitations in industrial formulation development as a delivery system.

Nanoampere-Level Piezoelectric Energy Harvesting Performance of Lithography-Free Centimeter-Scale MoS2 Monolayer Film Generators.

2D transition-metal dichalcogenides have been reported to possess piezoelectricity due to their lack of inversion symmetry; thus, they are potentially applicable as electromechanical energy harvesters. Herein, the authors propose a lithography-free piezoelectric energy harvester composed of centimeter-scale MoS2 monolayer films with an interdigitated electrode pattern that is enabled only by the large scale of the film. High-quality large-scale synthesis of the monolayer films is conducted by low-pressure chemical vapor deposition with the assistance of an unprecedented Na2 S promoter. The extra sulfur supplied by Na2 S critically passivates the sulfur vacancies. The energy harvester having a large active area of ≈18.3 mm2 demonstrates an unexpectedly high piezoelectric energy harvesting performance of ≈400.4 mV and ≈40.7 nA under a bending strain of 0.57%, with the careful adjustment of side electrodes along the zigzag atomic arrays in the two dominant domain structure. Nanoampere-level harvesting has not yet been reported with any 2D material-based harvester.

Development of a Planar Haptic Robot With Minimized Impedance.

Several studies have reported that stroke survivors displayed improved voluntary planar movements when forces supporting the upper limb increased, and when impeding forces decreased. Earlier haptic devices interacting with the human upper limb were potentially impacted by undesired residual friction force and device inertia. To explore natural, undisturbed voluntary motor control in stroke survivors, we describe the development of a Decoupled-Operational space Robot for wide Impedance Switching (DORIS) with minimized mechanical impedances. This design is based on a novel decoupling mechanism separating the end effector from a manipulator. While the user manipulates the end effector freely inside the workspace of the decoupling mechanism, to which a manipulator of the robot is attached, the robot detects such change in position using a lightweight linkage system. The manipulator of the robot then follows such movements of the end effector swiftly. Consequently, the user can explore the extended workspace, which can be as large as the manipulator's workspace. Since the end effector is mechanically decoupled from the manipulators and actuators, the user can remain unaffected by the mechanical impedances of the manipulator. Mechanical impedances perceived by the user and bandwidth of the control system were estimated. The developed robot was capable of detecting larger maximum acceleration and larger jerk of the reaching movement in chronic stroke survivors with hemiparesis. We propose that this device can be utilized for evaluating voluntary motor control of the upper limb while minimizing the impact of robot inertia and friction forces on limb behavior.

Five-Dimensional Optical Data Storage Based on Ellipse Orientation and Fluorescence Intensity in a Silver-Sensitized Commercial Glass.

Five-dimensional (5D) recording and decoding is demonstrated by using femtosecond direct laser writing in a silver-containing commercial glass. In particular, laser intensities and ellipse orientations generated by anamorphic focusing are employed to produce 5D data storage unit (3D for XYZ, 1D for the orientation of the elliptically-shaped data storage unit and 1D for its fluorescence intensity). In the recording process, two different images of a 4-bit bitmap format were simultaneously embedded in the medium by multiplexing the elliptical orientation of the laser focus and its intensity so as to access oriented elliptical patterns with independent fluorescence intensity. In the decoding process, two merged original images were successfully reconstructed by comparing each data storage unit with a fabricated calibration matrix of 16 × 16 levels for elliptic orientations and fluorescence intensities. We believe this technique can be applied to semi-permanent high-density data storage device.

Elbow training device using the Mechanically Adjustable Stiffness Actuator(MASA).

This paper presents an elbow training device using the Mechanically Adjustable Stiffness Actuator(MASA) for stroke survivors with hemiplegia. The MASA is a series elastic actuator whose mechanical stiffness is variable. Stiffness and the neutral position of the spring is mechanically changed using two identical actuators. Since assisting torque of the actuators is transmitted through the springs, changing stiffness of the MASA results in different level of assistance by the actuators. Then, according to the performance of the patients during given tracking tasks, the level of assistance is controlled via changing stiffness. A prototype of the rehabilitation device using the MASA is introduced and a preliminary experiments with 10 healthy subjects show the level of assistance changes.

Sub-diffraction-limited fluorescent patterns by tightly focusing polarized femtosecond vortex beams in a silver-containing glass.

We report that the shape and size of fluorescent patterns can be controlled by the focused laser intensity distribution, which depends on irradiation conditions as well as on the spin and orbital angular momenta being carried by light, inducing the formation of silver cluster patterns in a silver-containing zinc phosphate glass. In particular, we demonstrate that sub-diffraction-limited inner structures of fluorescent patterns can be generated by direct laser writing (DLW) with tightly focused femtosecond laser vortex beams as Laguerre-Gauss modes (LG0l) with linear and left-handed circular polarizations. We believe this technique, further combined with dual-color DLW, can be useful and powerful for developing structured light enabled nanostructures.

Enhanced Neurite Outgrowth by Intracellular Stimulation.

Electrical stimulation through direct electrical activation has been widely used to recover the function of neurons, primarily through the extracellular application of thin film electrodes. However, studies using extracellular methods show limited ability to reveal correlations between the cells and the electrical stimulation due to interference from external sources such as membrane capacitance and culture medium. Here, we demonstrate long-term intracellular electrical stimulation of undamaged pheochromocytoma (PC-12) cells by utilizing a vertical nanowire electrode array (VNEA). The VNEA was prepared by synthesizing silicon nanowires on a Si substrate through a vapor-liquid-solid (VLS) mechanism and then fabricating them into electrodes with semiconductor nanodevice processing. PC-12 cells were cultured on the VNEA for 4 days with intracellular electrical stimulation and then a 2-day stabilization period. Periodic scanning via two-photon microscopy confirmed that the electrodes pierced the cells without inducing damage. Electrical stimulation through the VNEA enhances cellular differentiation and neurite outgrowth by about 50% relative to extracellular stimulation under the same conditions. VNEA-mediated stimulation also revealed that cellular differentiation and growth in the cultures were dependent on the potential used to stimulate them. Intracellular stimulation using nanowires could pave the way for controlled cellular differentiation and outgrowth studies in living cells.

Vertical nanowire probes for intracellular signaling of living cells.

The single living cell action potential was measured in an intracellular mode by using a vertical nanoelectrode. For intracellular interfacing, Si nanowires were vertically grown in a controlled manner, and optimum conditions, such as diameter, length, and nanowire density, were determined by culturing cells on the nanowires. Vertical nanowire probes were then fabricated with a complimentary metal-oxide-semiconductor (CMOS) process including sequential deposition of the passivation and electrode layers on the nanowires, and a subsequent partial etching process. The fabricated nanowire probes had an approximately 60-nm diameter and were intracellular. These probes interfaced with a GH3 cell and measured the spontaneous action potential. It successfully measured the action potential, which rapidly reached a steady state with average peak amplitude of approximately 10 mV, duration of approximately 140 ms, and period of 0.9 Hz.

Synthesis of Si nanosheets by a chemical vapor deposition process and their blue emissions.

We synthesized free-standing Si nanosheets (NSs) with a thickness of about <2 nm using a chemical vapor deposition process and studied their optical properties. The Si NSs were formed by the formation of frameworks first along six different <110> directions normal to [111], its zone axis, and then by filling the spaces between the frameworks along the <112> directions under high flow rate of processing gas. The Si NSs showed blue emission at 435 nm, and absorbance and photoluminescence (PL) excitation measurements indicate that enhanced direct band transition attributes to the emission. Time-resolved PL measurement, which showed PL emission at 435 nm and a radiative lifetime of 1.346 ns, also indicates the enhanced direct band gap transition in these Si NSs. These outcomes indicate that dimensionality of Si nanostructures may affect the band gap transition and, in turn, the optical properties.

Coupling of semiconductor nanowires with neurons and their interfacial structure.

We report on the compatibility of various nanowires with hippocampal neurons and the structural study of the neuron-nanowire interface. Si, Ge, SiGe, and GaN nanowires are compatible with hippocampal neurons due to their native oxide, but ZnO nanowires are toxic to neuron due to a release of Zn ion. The interfaces of fixed Si nanowire and hippocampal neuron, cross-sectional samples, were prepared by focused ion beam and observed by transmission electron microscopy. The results showed that the processes of neuron were adhered well on the nanowire without cleft.

A correlated force-optical study on the self-assembly behavior of annexin V on model membranes: effect of dye conjugation.

We have examined the self-assembled membrane-bound aggregates of two annexin V (A5) dye conjugates and compared them to those from native A5. Native A5 and FITC-labeled A5 (A5-FITC) both formed discrete well-defined crystalline monolayer domains of p6 symmetry. However, A5-FITC also showed additional domains with a corrugated appearance not observed in native A5. In contrast, Cy3-labeled A5 (A5-Cy3) showed a mixture of crystalline monolayer and irregular multilayered domains, with the ratio of the two types varying significantly from sample to sample, and also required a much longer incubation time than native A5 and A5-FITC. When A5-FITC and A5-Cy3 were co-incubated on the same bilayer, well-defined crystalline monolayer domains containing both A5-FITC and A5-Cy3 were consistently observed at a much shorter incubation time than that of pure A5-Cy3 alone, indicating that A5-FITC facilitates the inclusion of A5-Cy3. These results suggest that dye labels can affect A5 2D self-assembly and crystal formation on membrane surfaces.

Observation of red-shifted strong surface plasmon scattering in single Cu nanowires.

Surface plasmon scattering spectra of chemically produced single Cu nanowires were obtained using a total internal reflection microscope. In particular, we have observed a strong surface plasmon peak in the far red and a red-shift of the surface plasmon resonance with increasing nanowire diameter. We believe that the most reasonable origin for the red-shift of comparably large diameter nanowires is the phase retardation effect.

Local field-induced optical properties of Ag-coated CdS quantum dots.

Local field-induced optical properties of Ag-coated CdS quantum dot structures are investigated. We experimentally observe a clear exciton peak due to the quantum confinement effect in uncoated CdS quantum dots, and surface plasmon resonance and red-shifted exciton peak in Ag-coated CdS composite quantum dot structures. We have calculated the Stark shift of the exciton peak as a function of the local field for different silver thicknesses and various sizes of quantum dots based on the effective-mass Hamiltonian using the numerical-matrix-diagonalization method. Our theoretical calculations strongly indicate that the exciton peak is red-shifted in the metal-semiconductor composite quantum dots due to a strong local field, i.e., the quantum confined Stark effect.

Anisotropy of near-field speckle patterns.

In the vicinity of a rough interface under normal illumination the speckle field has been found to be anisotropic; that is, its correlation length is much larger in the direction of polarization than in the perpendicular direction, forming stripe-shaped speckle patterns in the near-field region. Furthermore, with increasing distance from the interface, the anisotropy of the near-field speckles decays rapidly, while the speckle size increases drastically in all directions. Based on detailed analysis, it was found that the anisotropy of the near-field speckle patterns can be attributed to polarization-dependent coupling among the evanescent waves from different surface diffusers.

Numerical analysis of an annular-aperture solid immersion lens.

A physical model of an annular-aperture solid immersion lens (SIL) is proposed, and its attractive features are presented numerically with the finite-difference time-domain method. Placing an appropriate annular aperture in front of the SIL shows that the focal depth can evidently be improved, combining the virtues of the annular-aperture technique and the SIL technique. With this proposed method the rigorous distance control condition in related devices can be relaxed, preventing scratches or collisions between the optical head and the recording medium. Potentially, this technique could have great prospects for applications in optical data recording, lithography, and other applications that depend on immersion media to meet the resolution criteria across the image field.

Finite-difference time-domain analysis of self-focusing in a nonlinear Kerr film.

By using a finite-difference time-domain method, we analyze self-focusing effects in a nonlinear Kerr film and demonstrate that the near-field intensity distribution at the film surface can reach a stable state at only a few hundred femtoseconds after the incidence of the beam. Our simulations also show that the formation of multiple filamentations in the near-field is quite sensitive to the thickness of the nonlinear film and the power of the laser beam, strongly indicating the existence of nonlinear Fabry-Perot interference effects of the linearly polarized incident light.

Evolution of electromagnetic interference through nano-metallic double-slit.

We investigated the characteristics of the near- and far-field regions of the interference for nano-metallic double-slits using a two-dimensional finite-difference time-domain (FDTD) method. We have found that the patterns in the near-field region have a phase difference of pi with respect to those in the far-field region. A boundary, which separates the interference patterns of the two regions exists as a half circle and grows as the distance between the two slits increase. It is also found that evanescent waves can be enhanced and confined by coating the double-slit with a dielectric cladding.

Enhancement of shear-force sensitivity using asymmetric response of tuning forks for near-field scanning optical microscopy.

Resonance characteristics of a tuning fork are investigated to enhance the shear-force detection sensitivity for near-field scanning optical microscopy. In particular, we show that the asymmetric frequency response of a tuning fork can be utilized to increase quality factors and suppress the background feedback signal. The pinning down effect on one side of the main peak can readily elevate vertical sensitivity and stability. A simplified model based on a coupled harmonic oscillator is presented to describe the asymmetric resonance behavior of the tuning fork. We also show improved topographic images of a blue-ray disc and optical images of a chromium pattern on the quartz using the asymmetric resonance.

Polarization and detection angle dependence of interferometric imaging with scattering near-field scanning optical microscope.

Polarized images generated by the scattering near-field scanning optical microscopic interferometer were numerically studied by modeling the interferometer as a coupled point-dipole system. It was shown that, for a given specimen, the resolution of the near-field intensity and phase images were strongly dependent on both the polarization-direction of the reference light and the position of the far-field detector, revealing the strong polarization dependence of the near-field images. In the case of evanescent illumination, highly accurate images could be realized only when the detector was placed at a large enough view angle with the specimen and the reference light was polarized in the detecting-plane, which is vertical to the sample plane and contains both the detection point and the probe-tip.

Phase-shifting lateral shearing interferometer with two pairs of wedge plates.

We present a compact and robust phase-shifting lateral shearing interferometer that produces shearing fringes in orthogonal directions without any mechanical rotation or precise alignment. It consists of two pairs of wedge plates, a beam splitter, and a single CCD camera. Both phase-shifting and tilt for lateral shearing are achieved with two pairs of wedge plates, which can reduce systematic errors caused by external vibration and atmospheric disturbance.