Hydrogel Magnetomechanical Actuator Nanoparticles for Wireless Remote Control of Mechanosignaling In Vivo.

As a new enabling nanotechnology tool for wireless, target-specific, and long-distance stimulation of mechanoreceptors in vivo, here we present a hydrogel magnetomechanical actuator (h-MMA) nanoparticle. To allow both deep-tissue penetration of input signals and efficient force generation, h-MMA integrates a two-step transduction mechanism that converts magnetic anisotropic energy to thermal energy within its magnetic core (i.e., Zn0.4Fe2.6O4 nanoparticle cluster) and then to mechanical energy to induce the surrounding polymer (i.e., pNiPMAm) shell contraction, finally delivering forces to activate targeted mechanoreceptors. We show that h-MMAs enable on-demand modulation of Notch signaling in both fluorescence reporter cell lines and a xenograft mouse model, demonstrating its utility as a powerful in vivo perturbation approach for mechanobiology interrogation in a minimally invasive and untethered manner.

Non-contact long-range magnetic stimulation of mechanosensitive ion channels in freely moving animals.

Among physical stimulation modalities, magnetism has clear advantages, such as deep penetration and untethered interventions in biological subjects. However, some of the working principles and effectiveness of existing magnetic neurostimulation approaches have been challenged, leaving questions to be answered. Here we introduce m-Torquer, a magnetic toolkit that mimics magnetoreception in nature. It comprises a nanoscale magnetic torque actuator and a circular magnet array, which deliver piconewton-scale forces to cells over a working range of ~70 cm. With m-Torquer, stimulation of neurons expressing bona fide mechanosensitive ion channel Piezo1 enables consistent and reproducible neuromodulation in freely moving mice. With its long working distance and cellular targeting capability, m-Torquer provides versatility in its use, which can range from single cells to in vivo systems, with the potential application in large animals such as primates.

Chemical Transformations of Anisotropic Platelets and Spherical Nanocrystals.

ConspectusInorganic nanocrystal design has been continuously evolving with a better understanding of the chemical reaction mechanisms between chemical stimuli and nanocrystals. Under certain conditions, molecular compounds can be effective as chemical stimuli to induce transformative reactions of nanocrystals toward new materials that would differ in geometric shape, composition, and crystallographic structure. To explore such evolutionary processes, two-dimensional (2D) layered transition-metal chalcogenide (TMC) nanostructures are an interesting structural platform because they not only exhibit unique transformation pathways due to their structural anisotropy but also present new opportunities for improved material properties for potential applications such as catalysis and energy conversion and storage. The high surface area/volume ratio, interlayer van der Waals (vdW) spacing, and different coordination states between the unsaturated edges and the fully saturated basal planes of the chalcogens are characteristic of 2D layered TMC nanostructures, which subsequently lead to anisotropic chemical processes during chemical transformations, such as regioselective reactions at the interfacial boundaries in the pathways for either porous or solid heteronanostructures. In this Account, we first discuss the chemical reactivity of 2D layered TMC nanostructures. By categorizing the external stimuli in terms of chemical principles, such as Lewis acid-base chemistry, a desirable regioselective chemical reaction can occur with controlled reactivity. In association with the knowledge obtained from the nanoscale chemical reactivity of 2D layered nanocrystals, similar efforts in other important morphologies such as 1D and isotropic 0D nanocrystals are introduced. For instance, for 1D and 0D metal oxide nanocrystals, the effects of molecular stimuli on the atomic-level changes in the crystal lattice are demonstrated, eventually leading to a variety of shape transformations.

Magnetothermally Activated Nanometer-level Modular Functional Group Grafting of Nanoparticles.

Nanoparticles with multifunctionality and high colloidal stability are essential for biomedical applications. However, their use is often hindered by the formation of thick coating shells and/or nanoparticle agglomeration. Herein, we report a single nanoparticle coating strategy to form 1 nm polymeric shells with a variety of chemical functional groups and surface charges. Under exposure to alternating magnetic field, nanosecond thermal energy pulses trigger a polymerization in the region only a few nanometers from the magnetic nanoparticle (MNP) surface. Modular coatings containing functional groups, according to the respective choice of monomers, are possible. In addition, the surface charge can be tuned from negative through neutral to positive. We adopted a coating method for use in biomedical targeting studies where obtaining compact nanoparticles with the desired surface charge is critical. A single MNP with a zwitterionic charge can provide excellent colloidal stability and cell-specific targeting.

Morphology-Conserving Non-Kirkendall Anion Exchange of Metal Oxide Nanocrystals.

Nanoscale dynamic processes such as the diffusion of ions within solid-state structures are critical for understanding and tuning material properties in a wide range of areas, such as energy storage and conversion, catalysis, and optoelectronics. In the generation of new types of nanocrystals (NCs), diffusion-mediated ion exchange reactions have also been proposed as one of the most effective transformational strategies. However, retaining the original morphology and crystal structure of metal oxide NCs has been challenging because of Kirkendall void formation, and there has been no success, especially for anion exchange. Here we show that with the aid of an oxygen extracting reagent (OER), anion diffusion is dramatically accelerated and morphology-conserving anion exchange without Kirkendall void formation is possible. In the case of the conversion of Fe3O4 to Fe3S4, oxygen extraction and subsequent formation of the amorphous phase facilitate the migration of incoming sulfur anions by approximately 100-fold, which is close to the level of the outgoing cation diffusivity. We also demonstrate that the working principle of the morphology-conserving non-Kirkendall anion exchange is operative for metal oxide NCs with different shapes and crystal structures.

Fourier digital holography of real scenes for 360° tabletop holographic displays.

Recently, the tabletop holographic display has been introduced to present a large 3D hologram floating over the table. When the observer looks down at the hologram, the display reconstructs upper perspectives of the object at a 45° angle. This paper presents the full imaging chain for the tabletop holographic display based on capture, processing, and reconstruction of a 360° observable hologram of the real object. Two different imaging methods, which involve lensless Fourier digital holographic recordings and the tabletop holographic display, are introduced. The first method utilizes the conventional capture approach with a side view perspective and numerical tilt correction for 45° angular mismatch between the acquisition and reconstruction systems. The second method presents a modified lensless digital Fourier holography for holographic recording of the upper perspective. Experimental results including numerical and optical reconstructions present various visual aspects of both capture approaches such as viewpoint correction, refocusing, 3D effects, and 3D deformations.

Ultrathin Interface Regime of Core-Shell Magnetic Nanoparticles for Effective Magnetism Tailoring.

The magnetic exchange coupling interaction between hard and soft magnetic phases has been important for tailoring nanoscale magnetism, but spin interactions at the core-shell interface have not been well studied. Here, we systematically investigated a new interface phenomenon termed enhanced spin canting (ESC), which is operative when the shell thickness becomes ultrathin, a few atomic layers, and exhibits a large enhancement of magnetic coercivity (HC). We found that ESC arises not from the typical hard-soft exchange coupling but rather from the large magnetic surface anisotropy (KS) of the ultrathin interface. Due to this large increase in magnetism, ultrathin core-shell nanoparticles overreach the theoretical limit of magnetic energy product ((BH)max) and exhibit one of the largest values of specific loss power (SLP), which testifies to their potential capability as an effective mediator of magnetic energy conversion.

Quantitative Measurements of Size-Dependent Magnetoelectric Coupling in Fe3O4 Nanoparticles.

Bulk magnetite (Fe3O4), the loadstone used in magnetic compasses, has been known to exhibit magnetoelectric (ME) properties below ∼10 K; however, corresponding ME effects in Fe3O4 nanoparticles have been enigmatic. We investigate quantitatively the ME coupling of spherical Fe3O4 nanoparticles with uniform diameters (d) from 3 to 15 nm embedded in an insulating host, using a sensitive ME susceptometer. The intrinsic ME susceptibility (MES) of the Fe3O4 nanoparticles is measured, exhibiting a maximum value of ∼0.6 ps/m at 5 K for d = 15 nm. We found that the MES is reduced with reduced d but remains finite until d = ∼5 nm, which is close to the critical thickness for observing the Verwey transition. Moreover, with reduced diameter the critical temperature below which the MES becomes conspicuous increased systematically from 9.8 K in the bulk to 19.7 K in the nanoparticles with d = 7 nm, reflecting the core-shell effect on the ME properties. These results point to a new pathway for investigating ME effect in various nanomaterials.

360-degree tabletop electronic holographic display.

We demonstrate a tabletop holographic display system for simultaneously serving continuous parallax 3.2-inch 360-degree three-dimensional holographic image content to multiple observers at a 45-degree oblique viewing circumference. To achieve this, localized viewing windows are to be seamlessly generated on the 360-degree viewing circumference. In the proposed system, four synchronized high-speed digital micro-mirror displays are optically configured to comprise a single 2 by 2 multi-vision panel that enables size enlargement and time-division-multiplexing of holographic image content. Also, a specially designed optical image delivery sub-system that is composed of parabolic mirrors and an aspheric lens is designed as an essential part for achieving an enlarged 3.2-inch holographic image and a large 45-degree oblique viewing angle without visual distortion.

Fourier Surfaces Reaching Full-Color Diffraction Limits.

Optical Fourier surfaces (OFSs), characterized by sinusoidally profiled diffractive optical elements, can outperform traditional binary-type counterparts by minimizing optical noise through selectively driving diffraction at desired frequencies. While scanning probe lithography (SPL), gray-scale electron beam lithography (EBL), and holographic inscriptions are effective for fabricating OFSs, achieving full-color diffractions at fundamental efficiency limits is challenging. Here, an integrated manufacturing process is presented, validated theoretically and experimentally, for fully transparent OFSs reaching the fundamental limit of diffraction efficiency. Leveraging holographic inscriptions and soft nanoimprinting, this approach effectively addresses challenges in conventional OFS manufacturing, enabling scalable production of noise-free and maximally efficient OFSs with record-high throughput (1010-1012 µm2 h-1), surpassing SPL and EBL by 1010 times. Toward this end, a wafer-scale OFSs array is demonstrated consisting of full-color diffractive gratings, color graphics, and microlenses by the one-step nanoimprinting, which is readily compatible with rapid prototyping of OFSs even on curved panels, demanding for transformative optical devices such as augmented and virtual reality displays.

Nanoscale magnetism control via surface and exchange anisotropy for optimized ferrimagnetic hysteresis.

With the aim of controlling nanoscale magnetism, we demonstrate an approach encompassing concepts of surface and exchange anisotropy while reflecting size, shape, and structural hybridization of nanoparticles. We visualize that cube has higher magnetization value than sphere with highest coercivity at 60 nm. Its hybridization into core-shell (CS) structure brings about a 14-fold increase in the coercivity with an exceptional energy conversion of magnetic field into thermal energy of 10600 W/g, the largest reported to date. Such capability of the CS-cube is highly effective for drug resistant cancer cell treatment.

Transflective digital holographic microscopy and its use for probing plasmonic light beaming.

We present a novel digital holographic microscopy technique termed transflective digital holographic microscopy in order to probe plasmonic beaming fields and to view their platform structures. Here, we borrow the term, 'transflective', a portmanteau meaning a blend of transmission and reflection according to the light-collecting condition, which is conventionally used in liquid crystal display systems. Incorporating the transmission type holographic microscopy with the reflection type, achieved by the utilization of polarization property of coherent light waves, we propose an application of the system to probing the beam path and its corresponding structure in plasmonic beaming phenomena.

A compact light concentrator by the use of plasmonic faced folded nano-rods.

We propose a compact nano-metallic structure for enhancing and concentrating far-field transmission: a faced folded nano-rod (FFR) unit, composed of two folded metallic nano-rods placed facing each other in an aperture. By analyzing local charge, field, and current distributions in the FFR unit using three-dimensional finite difference time domain (FDTD) calculation results, we show that although charge and field configurations become somewhat different depending on the polarization states of the illumination, similar current flows are formed in the FFR unit, which entail similar far-field radiation patterns regardless of the polarization states, making the FFR unit a quasi-polarization-insensitive field concentrator. We demonstrate this functionality of the FFR unit experimentally using the holographic microscopy which provides us a three-dimensional map of the complex wavefronts of optical fields emanating from the FFR unit.

Phase-conjugate holographic lithography based on micromirror array recording.

We present phase-conjugate holographic lithography with a hologram recorded by a digital micromirror device (DMD) and a telecentric lens. In our lithography system, a phase-conjugate hologram is applied instead of conventional masks or reticles to form patterns. This method has the advantage of increasing focus range, and it is applicable to the formation of patterns on fairly uneven surfaces. The hologram pattern is dynamically generated by the DMD, and its resolution is mainly determined by the demagnification of the telecentric lens. We experimentally demonstrate that our holographic lithographic system has a large focus range, and it is feasible to make a large-area hologram by stitching each pattern generated by the DMD without a falling off in resolution.

High-resolution T1 MRI via renally clearable dextran nanoparticles with an iron oxide shell.

Contrast agents for magnetic resonance imaging (MRI) improve anatomical visualizations. However, owing to poor image resolution in whole-body MRI, resolving fine structures is challenging. Here, we report that a nanoparticle with a polysaccharide supramolecular core and a shell of amorphous-like hydrous ferric oxide generating strong T1 MRI contrast (with a relaxivity coefficient ratio of ~1.2) facilitates the imaging, at resolutions of the order of a few hundred micrometres, of cerebral, coronary and peripheral microvessels in rodents and of lower-extremity vessels in rabbits. The nanoparticle can be synthesized at room temperature in aqueous solution and in the absence of surfactants, has blood circulation and renal clearance profiles that prevent opsonization, and leads to better imaging performance than Dotarem (gadoterate meglumine), a clinically approved gadolinium-based MRI contrast agent. The nanoparticle's biocompatibility and imaging performance may prove advantageous in a broad range of preclinical and clinical applications of MRI.

Analysis of the coupling of light into a metal-dielectric composite waveguide structure and its application for use as a wavelength-band selection filter.

We analyzed and experimentally tested a metal-dielectric composite waveguide structure. After coating the surface of the metal layer in the Kretschmann attenuated total internal reflection configuration with a dielectric layer, we explain the coupling of incident light into the coated layer. After finding the dispersion relationships for the layered media including the metal-dielectric composite waveguide, we can determine a solution for its existence in a complex domain. By inscribing a periodic grating structure in the dielectric layer of the metal-dielectric composite waveguide, we experimentally verify the coupling of incident light on the metal-dielectric composite waveguide structure and propose its application for use as a wavelength-band selection filter.

Optical beam focusing with a metal slit array arranged along a semicircular surface and its optimization with a genetic algorithm.

A metal slit array arranged along a semicircular surface achieving subwavelength optical beam focusing along the lateral direction is proposed. Taking into consideration surface plasmon polaritons that pass through a metal slit array, we design the array with a curvature. By use of a genetic algorithm, the size of the metal slit and the corresponding curvature are to be determined. Based on our metal slit array configuration, the full width at half-maximum can be achieved on a subwavelength scale.

Wide viewing angle dynamic holographic stereogram with a curved array of spatial light modulators.

A novel design of dynamic holographic stereogram with a curved array of spatial light modulators (SLMs) is proposed. In general, it is difficult to simultaneously achieve a wide viewing angle and an available width for the digital holographic display. Moreover, the wide viewing angle of a display system needs a large optical numerical aperture where the paraxial approximation fails, and thus an extremely large planar SLM is necessary in using previous methods. To solve this problem, our proposed display system is composed of a curved array of SLMs to obtain a large number of data points and reduce the spatial bandwidth in SLMs. In the curved array of SLMs, each SLM is individually transformed to display local angular spectra of object wave, which is based on a fundamental idea of holographic stereogram. To embody the dynamic holographic stereogram with SLMs, each SLM is effectively reformed for simplifying the optical structure and reducing the light power loss. In detail, spatially modulated wave is optically divided and transformed, as if each SLM were composed of three sub-SLMs. This design improves the scalability in viewing angle of holographic display and the loss of light power is significantly reduced. With this method, we can achieve the digital holographic display with 22.8 degrees viewing angle.