Label-free and liquid state SERS detection of multi-scaled bioanalytes via light-induced pinpoint colloidal assembly.

Surface-enhanced Raman scattering (SERS) has been extensively applied to detect complex analytes due to its ability to enhance the fingerprint signals of molecules around nanostructured metallic surfaces. Thus, it is essential to design SERS-active nanostructures with abundant electromagnetic hotspots in a probed volume according to the dimensions of the analytes, as the analytes must be located in their hotspots for maximum signal enhancement. Herein, we demonstrate a simple method for detecting robust SERS signals from multi-scaled bioanalytes, regardless of their dimensions in the liquid state, through a photothermally driven co-assembly with colloidal plasmonic nanoparticles as signal enhancers.

Challenges and Recent Analytical Advances in Micro/Nanoplastic Detection.

Despite growing ecological concerns, studies on microplastics and nanoplastics are still in their initial stages owing to technical hurdles in analytical techniques, especially for nanoplastics. We provide an overview of the general attributes of micro/nanoplastics in natural environments and analytical techniques commonly used for their analysis. After demonstrating the analytical challenges associated with the identification of nanoplastics due to their distinctive characteristics, we discuss recent technological advancements for detecting nanoplastics.

Advancements of Intense Terahertz Field Focusing on Metallic Nanoarchitectures for Monitoring Hidden Interatomic Gas-Matter Interactions.

With the advancements of nanotechnology, innovative photonic designs coupled with functional materials provide a unique way to acquire, share, and respond effectively to information. It is found that the simple deposition of a 30 nm-thick palladium nanofilm on a terahertz (THz) metasurface chip with a 14 nm-wide effective nanogap of asymmetric materials and geometries allows the tracking of both interatomic and interfacial gas-matter interactions, including gas adsorption, hydrogenation (or dehydrogenation), metal phase changes, and unique water-forming reactions. Combinatorial analyses by simulation and experimental measurements demonstrate the distinct nanostructures, which leads to significant light-matter interactions and corresponding THz absorption in a real-time, highly repeatable, and reliable manner.

Fabry-Perot Cavity Control for Tunable Raman Scattering.

The Fabry-Perot (FP) resonator is an intuitive and versatile optical structure owing to its uniqueness in light-matter interactions, yielding resonance with a wide range of wavelengths as it couples with photonic materials encapsulated in a dielectric cavity. Leveraging the FP resonator for molecular detection, a simple geometry of the metal-dielectric-metal structure is demonstrated to allow tuning of the enhancement factors (EFs) of surface-enhanced Raman scattering (SERS). The optimum near-field EF from randomly dispersed gold nano-gaps and dynamic modulation of the far-field SERS EF by varying the optical resonance of the FP etalon are systematically investigated by performing computational and experimental analyses.

Real-Time Underwater Nanoplastic Detection beyond the Diffusion Limit and Low Raman Scattering Cross-Section Electro-Photonic Tweezers.

Emerging as substantial concerns in the ecosystem, submicron plastics have attracted much attention for their considerable hazards. However, their effect and even amount in the environment remain unclear. Establishing a substantive analytic platform is essential to expand the understanding of nanoplastics.

In Vitro Membrane Platform for the Visualization of Water Impermeability across the Liquid-Ordered Phase under Hypertonic Conditions.

Passive water penetration across the cell membrane by osmotic diffusion is essential for the homeostasis of cell volume, in addition to the protein-assisted active transportation of water. Since membrane components can regulate water permeability, controlling compositional variation during the volume regulatory process is a prerequisite for investigating the underlying mechanisms of water permeation and related membrane dynamics. However, the lack of a viable in vitro membrane platform in hypertonic solutions impedes advanced knowledge of cell volume regulation processes, especially cholesterol-enriched lipid domains called lipid rafts.

Development of a Photonic Switch via Electro-Capillarity-Induced Water Penetration Across a 10-nm Gap.

With narrow and dense nanoarchitectures increasingly adopted to improve optical functionality, achieving the complete wetting of photonic devices is required when aiming at underwater molecule detection over the water-repellent optical materials. Despite continuous advances in photonic applications, real-time monitoring of nanoscale wetting transitions across nanostructures with 10-nm gaps, the distance at which photonic performance is maximized, remains a chronic hurdle when attempting to quantify the water influx and molecules therein. For this reason, the present study develops a photonic switch that transforms the wetting transition into perceivable color changes using a liquid-permeable Fabry-Perot resonator.

Ionic contrast across a lipid membrane for Debye length extension: towards an ultimate bioelectronic transducer.

Despite technological advances in biomolecule detections, evaluation of molecular interactions via potentiometric devices under ion-enriched solutions has remained a long-standing problem. To avoid severe performance degradation of bioelectronics by ionic screening effects, we cover probe surfaces of field effect transistors with a single film of the supported lipid bilayer, and realize respectable potentiometric signals from receptor-ligand bindings irrespective of ionic strength of bulky solutions by placing an ion-free water layer underneath the supported lipid bilayer. High-energy X-ray reflectometry together with the circuit analysis and molecular dynamics simulation discovered biochemical findings that effective electrical signals dominantly originated from the sub-nanoscale conformational change of lipids in the course of receptor-ligand bindings.

Nanoscale Terahertz Monitoring on Multiphase Dynamic Assembly of Nanoparticles under Aqueous Environment.

Probing the kinetic evolution of nanoparticle (NP) growth in liquids is essential for understanding complex nano-phases and their corresponding functions. Terahertz (THz) sensing, an emerging technology for next-generation laser photonics, has been developed with unique photonic features, including label-free, non-destructive, and molecular-specific spectral characteristics. Recently, metasurface-based sensing platforms have helped trace biomolecules by overcoming low THz absorption cross-sectional limits.

Autofluorescence-Raman Mapping Integration analysis for ultra-fast label-free monitoring of adipogenic differentiation of stem cells.

Stem cell-based therapies have recently emerged to treat various incurable diseases and disorders. Types of stem cell-derived cells and their functions should be intensively analyzed before therapy. However, current pre-treatment steps for biological analysis are mostly destructive.

Direct comparison with terahertz metamaterials and surface-enhanced Raman scattering in a molecular-specific sensing performance.

Signal enhancement of spectroscopies including terahertz time-domain spectroscopy (THz-TDS) and surface-enhanced Raman scattering (SERS) is a critical issue for effective molecular detection and identification. In this study, the sensing performance between THz-TDS and SERS individually accompanied by the proper plasmonic subwavelength structures was compared. For the precisely quantitative study on the optical properties of rhodamine 6G (R6G) dyes, SERS incorporates with the non-linearly enhanced Raman emissions at the molecular characteristic peaks while THz-TDS refers to the transmittance change and the shift of the spectral resonance.

Asymmetric optical camouflage: tuneable reflective colour accompanied by the optical Janus effect.

Going beyond an improved colour gamut, an asymmetric colour contrast, which depends on the viewing direction, and its ability to readily deliver information could create opportunities for a wide range of applications, such as next-generation optical switches, colour displays, and security features in anti-counterfeiting devices. Here, we propose a simple Fabry-Perot etalon architecture capable of generating viewing-direction-sensitive colour contrasts and encrypting pre-inscribed information upon immersion in particular solvents (optical camouflage). Based on the experimental verification of the theoretical modelling, we have discovered a completely new and exotic optical phenomenon involving a tuneable colour switch for viewing-direction-dependent information delivery, which we define as asymmetric optical camouflage.

Label-free brain tissue imaging using large-area terahertz metamaterials.

Terahertz (THz) imaging technology has shown significant potential for use in biomedical imaging owing to its non-ionizing characteristics by its low photon energy and its ultrabroadband spectral comparability with many molecular vibrational resonances. However, despite the significant advantage of being able to identify bio-materials in label-free configurations, most meaningful signals are buried by huge water absorption, thus it is very difficult to distinguish them using the small differences in optical constants at THz regime, limiting the practical application of this technology. Here, we demonstrate advanced THz imaging with enhanced color contrast by the use of THz field that is localized and enhanced by a nanometer-scale slot array.

Time-Dependent Wetting Scenarios of a Water Droplet on Surface-Energy-Controlled Microcavity Structures with Functional Nanocoatings.

We report the surface-energy-dependent wetting transition characteristics of an evaporating water droplet on surface-energy-controlled microcavity structures with functional nanocoatings. The droplet wetting scenarios were categorized into four types depending on the synergistic effect of surface energy and pattern size. The silicon (Si) microcavity surfaces ( = 69.

Precise capture and dynamic relocation of nanoparticulate biomolecules through dielectrophoretic enhancement by vertical nanogap architectures.

Toward the development of surface-sensitive analytical techniques for biosensors and diagnostic biochip assays, a local integration of low-concentration target materials into the sensing region of interest is essential to improve the sensitivity and reliability of the devices. As a result, the dynamic process of sorting and accurate positioning the nanoparticulate biomolecules within pre-defined micro/nanostructures is critical, however, it remains a huge hurdle for the realization of practical surface-sensitive biosensors and biochips. A scalable, massive, and non-destructive trapping methodology based on dielectrophoretic forces is highly demanded for assembling nanoparticles and biosensing tools.

Compensation of spin-orbit interaction using the geometric phase of distributed nanoslits for polarization-independent plasmonic vortex generation.

A metasurface is a planar optical device that controls the phase, amplitude, and polarization of light through subwavelength-scale unit elements, called meta-atom. The tunability of plasmonic vortex lens (PVL) which generates surface plasmon polaritons (SPPs) carrying orbital angular momentum can be improved by using meta-atom. However, conventional PVLs exhibit nonuniform field profiles according to the incident polarization states owing to the spin-orbital interaction (SOI) effect observed during SPP excitation.

Kinetics of lipid raft formation at lipid monolayer-bilayer junction probed by surface plasmon resonance.

A label-free, non-dispruptive, and real-time analytical device to monitor the dynamic features of biomolecules and their interactions with neighboring molecules is an essential prerequisite for biochip- and diagonostic assays. To explore one of the central questions on the lipid-lipid interactions in the course of the liquid-ordered (l) domain formation, called rafts, we developed a method of reconstituting continuous but spatially heterogeneous lipid membrane platforms with molayer-bilayer juntions (MBJs) that enable to form the l domains in a spatiotemporally controlled manner. This allows us to detect the time-lapse dynamics of the lipid-lipid interactions during raft formation and resultant membrane phase changes together with the raft-associated receptor-ligand binding through the surface plasmon resonance (SPR).

Surface Correlation-Based Fingerprinting Method Using LTE Signal for Localization in Urban Canyon.

The Global Satellite Navigation System (GNSS) used in various location-based services is accurate and stable in outdoor environments. However, it cannot be utilized in an indoor environment because of low signal availability and degradation of accuracy due to the multipath distortion of satellite signals in urban areas. On the contrary, LTE signals are available almost everywhere in urban areas and are quite stable without much variation throughout the year.

Highly Sensitive Color Tunablility by Scalable Nanomorphology of a Dielectric Layer in Liquid-Permeable Metal-Insulator-Metal Structure.

A liquid-permeable concept in a metal-insulator-metal (MIM) structure is proposed to achieve highly sensitive color-tuning property through the change of the effective refractive index of the dielectric insulator layer. A semicontinuous top metal film with nanoapertures, adopted as a transreflective layer for MIM resonator, allows to tailor the nanomorphology of a dielectric layer through selective etching of the underneath insulator layer, resulting in nanopillars and hollow voids in the insulator layer. By allowing outer mediums to enter into the hollow voids of the dielectric layer, such liquid-permeable MIM architecture enables to achieve the wavelength shift as large as 323.

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.

Ultrasensitive terahertz sensing of gold nanoparticles inside nano slot antennas.

We introduce a robust control method of terahertz (THz) transmission by tuning filling factors of Au nanoparticles (AuNPs) inside nano slot antennas. AuNPs in sub-100 nm diameters were spread over the nano slot antennas, followed by sweeping them into the slots. AuNPs can be efficiently localized and inserted into nano slots where the THz fields are greatly enhanced, by a "squeegee" made of the polydimethylsiloxane (PDMS).

Dynamic Manipulation of Charged Lipids in Model Membrane for Bio-Microarrays.

We describe the dynamic manipulation of the charged lipids in a confined geometry where two dispersive factors arising from the random diffusion-based Brownian motion and the field-induced drift of target lipids compete with each other. It is found that the lateral distribution of the target lipids is well controlled through a combined effect of an external electric field and the geometric restrictions by the confinement. The dynamic manipulation scheme for the charged lipids in two-dimension would be useful for understanding the spatial organization of membrane components in a supported lipid membrane mimicking a real cell membrane and for producing membrane-based microarrays.

Continuity of Monolayer-Bilayer Junctions for Localization of Lipid Raft Microdomains in Model Membranes.

We show that the selective localization of cholesterol-rich domains and associated ganglioside receptors prefer to occur in the monolayer across continuous monolayer-bilayer junctions (MBJs) in supported lipid membranes. For the MBJs, glass substrates were patterned with poly(dimethylsiloxane) (PDMS) oligomers by thermally-assisted contact printing, leaving behind 3 nm-thick PDMS patterns. The hydrophobicity of the transferred PDMS patterns was precisely tuned by the stamping temperature.

Lipid Membrane Deformation Accompanied by Disk-to-Ring Shape Transition of Cholesterol-Rich Domains.

During vesicle budding or endocytosis, biomembranes undergo a series of lipid- and protein-mediated deformations involving cholesterol-enriched lipid rafts. If lipid rafts of high bending rigidities become confined to the incipient curved membrane topology such as a bud-neck interface, they can be expected to reform as ring-shaped rafts. Here, we report on the observation of a disk-to-ring shape morpho-chemical transition of a model membrane in the absence of geometric constraints.