Long-term tracking of neural and oligodendroglial development in large-scale human cerebral organoids by noninvasive volumetric imaging.

Human cerebral organoids serve as a quintessential model for deciphering the complexities of brain development in a three-dimensional milieu. However, imaging these organoids, particularly when they exceed several millimeters in size, has been curtailed by the technical impediments such as phototoxicity, slow imaging speeds, and inadequate resolution and imaging depth. Addressing these pivotal challenges, our study has pioneered a high-speed scanning microscope, synergistically coupled with advanced computational image processing.

Cryptographic transistor for true random number generator with low power consumption.

We design a cryptographic transistor (cryptoristor)-based true random number generator (tRNG) with low power consumption and small footprint. This is the first attempt to use irregular and unpredictable operation-induced randomness of a cryptoristor as an entropy source. To extract discrete random numbers with a binary code from the cryptoristor, we developed a noise-coupling analog-to-digital converter.

Cryptographic triboelectric random number generator with gentle breezes of an entropy source.

A wind-driven triboelectric nanogenerator (W-TENG) is a promising energy harvesting device due to its clean, ubiquitous and unexhausted properties. In addition, a W-TENG induces unpredictable chaotic outputs from wind flow that can serve as an entropy source for cryptography. This can be applied to a true random number generator (TRNG) for a secured system due to its inherent turbulent nature; thus, a W-TENG with a two-in-one structure can simultaneously generate both power and true random numbers.

Analyses of unpredictable properties of a wind-driven triboelectric random number generator.

Wind-driven triboelectric nanogenerators (W-TENGs) are a promising candidate for an energy harvester because wind itself possesses unexhausted, ubiquitous, and clean properties. W-TENG has also been used as a random number generator (RNG) due to the inherent chaotic properties of wind that is also an entropy source. Thus, a W-TENG which simultaneously generates both power and true random numbers with a two-in-one structure, is a wind-driven RNG (W-RNG) like the Janus.

Exploiting volumetric wave correlation for enhanced depth imaging in scattering medium.

Imaging an object embedded within a scattering medium requires the correction of complex sample-induced wave distortions. Existing approaches have been designed to resolve them by optimizing signal waves recorded in each 2D image. Here, we present a volumetric image reconstruction framework that merges two fundamental degrees of freedom, the wavelength and propagation angles of light waves, based on the object momentum conservation principle.

Recent advances in optical imaging through deep tissue: imaging probes and techniques.

Optical imaging has been essential for scientific observations to date, however its biomedical applications has been restricted due to its poor penetration through tissues. In living tissue, signal attenuation and limited imaging depth caused by the wave distortion occur because of scattering and absorption of light by various molecules including hemoglobin, pigments, and water. To overcome this, methodologies have been proposed in the various fields, which can be mainly categorized into two stategies: developing new imaging probes and optical techniques.

Through-skull brain imaging in vivo at visible wavelengths via dimensionality reduction adaptive-optical microscopy.

Compensation of sample-induced optical aberrations is crucial for visualizing microscopic structures deep within biological tissues. However, strong multiple scattering poses a fundamental limitation for identifying and correcting the tissue-induced aberrations. Here, we introduce a label-free deep-tissue imaging technique termed dimensionality reduction adaptive-optical microscopy (DReAM) to selectively attenuate multiple scattering.

Triboelectric Nanogenerator: Structure, Mechanism, and Applications.

With the rapid development of the Internet of Things (IoT), the number of sensors utilized for the IoT is expected to exceed 200 billion by 2025. Thus, sustainable energy supplies without the recharging and replacement of the charge storage device have become increasingly important. Among various energy harvesters, the triboelectric nanogenerator (TENG) has attracted considerable attention due to its high instantaneous output power, broad selection of available materials, eco-friendly and inexpensive fabrication process, and various working modes customized for target applications.

Label-free neuroimaging in vivo using synchronous angular scanning microscopy with single-scattering accumulation algorithm.

Label-free in vivo imaging is crucial for elucidating the underlying mechanisms of many important biological systems in their most native states. However, the applicability of existing modalities has been limited to either superficial layers or early developmental stages due to tissue turbidity. Here, we report a synchronous angular scanning microscope for the rapid interferometric recording of the time-gated reflection matrix, which is a unique matrix characterizing full light-specimen interaction.

Selective Equatorial Sclera Crosslinking in the Orbit Using a Metal-Coated Polymer Waveguide.

Purpose: Photochemical crosslinking of the sclera is an emerging technique that may prevent excessive eye elongation in pathologic myopia by stiffening the scleral tissue. To overcome the challenge of uniform light delivery in an anatomically restricted space, we previously introduced the use of flexible polymer waveguides. We presently demonstrate advanced waveguides that are optimized to deliver light selectively to equatorial sclera in the intact orbit.

Microsphere-based interferometric optical probe.

Fluorescent optical probes have rapidly transformed our understanding of complex biological systems by providing specific information on biological targets in the natural living state. However, their utility is often limited by insufficient brightness, photostability, and multiplexing capacity. Here, we report a conceptually new optical probe, termed 'reflectophore', which is based on the spectral interference from a dielectric microsphere.

High-resolution adaptive optical imaging within thick scattering media using closed-loop accumulation of single scattering.

Thick biological tissues give rise to not only the multiple scattering of incoming light waves, but also the aberrations of remaining signal waves. The challenge for existing optical microscopy methods to overcome both problems simultaneously has limited sub-micron spatial resolution imaging to shallow depths. Here we present an optical coherence imaging method that can identify aberrations of waves incident to and reflected from the samples separately, and eliminate such aberrations even in the presence of multiple light scattering.

Label-free nanoscale optical metrology on myelinated axons in vivo.

In the mammalian nervous system, myelin provides electrical insulation for the neural circuit by forming a highly organized, multilayered thin film around the axon fibers. Here, we investigate the spectral reflectance from this subcellular nanostructure and devise a new label-free technique based on a spectroscopic analysis of reflected light, enabling nanoscale imaging of myelinated axons in their natural living state. Using this technique, we demonstrate three-dimensional mapping of the axon diameter and sensing of dynamic changes in the substructure of myelin at nanoscale.

Flexible Optical Waveguides for Uniform Periscleral Cross-Linking.

Purpose: Scleral cross-linking (SXL) with a photosensitizer and light is a potential strategy to mechanically reinforce the sclera and prevent progressive axial elongation responsible for severe myopia. Current approaches for light delivery to the sclera are cumbersome, do not provide uniform illumination, and only treat a limited area of sclera. To overcome these challenges, we developed flexible optical waveguides optimized for efficient, homogeneous light delivery.

Optical lens-microneedle array for percutaneous light delivery.

The limited penetration depth of light in skin tissues is a practical bottleneck in dermatologic applications of light-induced therapies, including anti-microbial blue light therapy and photodynamic skin cancer therapy. Here, we demonstrate a novel device, termed optical microneedle array (OMNA), for percutaneous light delivery. A prototype device with a 11 by 11 array of needles at a spacing of 1 mm and a length of 1.

Shear Brillouin light scattering microscope.

Brillouin spectroscopy has been used to characterize shear acoustic phonons in materials. However, conventional instruments had slow acquisition times over 10 min per 1 mW of input optical power, and they required two objective lenses to form a 90° scattering geometry necessary for polarization coupling by shear phonons. Here, we demonstrate a confocal Brillouin microscope capable of detecting both shear and longitudinal phonons with improved speeds and with a single objective lens.

Selective two-photon collagen crosslinking measured by Brillouin microscopy.

Two-photon polymerization has enabled precise microfabrication of three-dimensional structures with applications spanning from photonic microdevices, drug delivery systems, and cellular scaffolds. We present two-photon collagen crosslinking (2P-CXL) of intact corneal tissue using riboflavin and femtosecond laser irradiation. Collagen fiber orientations and photobleaching were characterized by second harmonic generation and two-photon fluorescence imaging, respectively.

Preferential coupling of an incident wave to reflection eigenchannels of disordered media.

Light waves incident to a highly scattering medium are incapable of penetrating deep into the medium due to the multiple scattering process. This poses a fundamental limitation to optically imaging, sensing, and manipulating targets embedded in opaque scattering layers such as biological tissues. One strategy for mitigating the shallow wave penetration is to exploit eigenchannels with anomalously high transmittance existing in any scattering medium.

Exploring anti-reflection modes in disordered media.

Sensing and manipulating targets hidden under scattering media are universal problems that take place in applications ranging from deep-tissue optical imaging to laser surgery. A major issue in these applications is the shallow light penetration caused by multiple scattering that reflects most of incident light. Although advances have been made to eliminate image distortion by a scattering medium, dealing with the light reflection has remained unchallenged.

Transmission matrix of a scattering medium and its applications in biophotonics.

A conventional lens has well-defined transfer function with which we can form an image of a target object. On the contrary, scattering media such as biological tissues, multimode optical fibers and layers of disordered nanoparticles have highly complex transfer function, which makes them impractical for the general imaging purpose. In recent studies, we presented a method of experimentally recording the transmission matrix of such media, which is a measure of the transfer function.

Toward a miniature endomicroscope: pixelation-free and diffraction-limited imaging through a fiber bundle.

A fiber bundle is widely used for endoscopic imaging due to its direct image delivery capability. However, there exists an inevitable pixelation artifact, which limits spatial resolution to the diameter of individual fibers. In this Letter, we present a method that can eliminate this artifact and achieve diffraction-limited spatial resolution.

Relation between transmission eigenchannels and single-channel optimizing modes in a disordered medium.

The wave transport through disordered media, although a random process, has some universal physical properties. One of these properties that has been investigated in this report is the relation between transmission eigenchannels and the so-called single-channel optimizing mode, which maximizes the intensity of the transmitted wave at a single specific output channel. Since single-channel optimizing modes have higher transmittance than the uncontrolled waves, it has been predicted before that transmission eigenchannels with higher transmittance preferentially contribute to the single-channel optimizing modes in proportion to the square of eigenvalues.

Disorder-mediated enhancement of fiber numerical aperture.

The numerical aperture (NA) of a multimode optical fiber sets the limit of the information transport capacity along the spatial degree of freedom. In this Letter, we report that the application of a highly disordered medium can overcome the capacity limit set by the fiber NA. Specifically, we coated the input surface of a multimode fiber with a disordered medium made of ZnO nanoparticles and transported a wide-field image through the fiber with a spatial resolution beyond the diffraction limit given by the fiber NA.

Sensitive and selective electrochemical detection of dopamine using an electrode modified with carboxylated carbonaceous spheres.

A highly sensitive and selective electrochemical sensor of dopamine (DA) has been developed by employing carboxylated carbonaceous spheres to modify glassy carbon electrodes (GCEs). Scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy were used to characterize as-prepared carbonaceous spheres. The results show that the diameter of carboxylated carbonaceous spheres is uniformly 500 nm and that their surfaces mainly expose carboxyl groups with negative charges.