Thin Layer Chromatography-Freeze Surface-Enhanced Raman Spectroscopy: A Powerful Tool for Monitoring Synthetic Reactions.

Thin layer chromatography (TLC) is widely used to confirm the formation of the target compound in chemical synthesis. The key issue in TLC is spot identification as it primarily relies on retention factors. Coupling of TLC with surface-enhanced Raman spectroscopy (SERS), which gives direct molecular information, is an appropriate choice, to overcome this challenge.

Freeze Surface-Enhanced Raman Scattering Coupled with Thin-Layer Chromatography: Pesticide Detection and Quantification Case.

Thin-layer chromatography (TLC) is widely used in various branches of chemical science to separate components in complex mixtures because of its simplicity. In most cases, analyte spots are visually detected by fluorescence, and the retention factor () is determined from the distance traveled by the analyte. Further characterizations are often necessary to identify separated chemicals because molecular information other than is not available.

Aqueous-nonaqueous solvent-switching ion chromatography of halide impurities in ionic liquids.

We here propose an efficient solvent-switching preconcentration method for the ion-chromatographic (IC) determination of halide impurities contained ionic liquids (ILs). Because halide impurities strongly affect the physicochemical properties of ILs, their analysis is an important task for the successful utilization of ILs. Although IC is an efficient method for this purpose, its application still involves significant challenges.

Surface-enhanced Raman scattering of DNA bases using frozen silver nanoparticle dispersion as a platform.

Raman spectroscopy is a powerful method to characterize molecules in various media. Although surface-enhanced Raman scattering (SERS) is often employed to compensate for the intrinsically poor sensitivity of Raman spectroscopy, there remain serious tasks, such as simple preparations of SERS substrates, sensitivity control, and reproducible measurements. Here, we propose freezing as an efficient way to overcome these problems in SERS measurements using DNA bases as model targets.

Microscale pH inhomogeneity in frozen NaCl solutions.

When an aqueous solution freezes at temperatures above the eutectic point, a freeze concentrated solution (FCS) is separated from the ice phase. Reactions of environmental importance often occur in the FCS and, in some cases, are accelerated compared to those in solution conditions. The pH of the FCS is an essential factor governing the thermodynamics and kinetics of the reactions occurring therein.

Quantification using statistical parameters derived from signal intensity distributions in surface enhanced Raman scattering (SERS).

Raman spectroscopy is a powerful method, which provides information on molecular structures, conformations, interactions etc. However, its applications are severely restricted because of low sensitivity. Although surface enhanced Raman scattering (SERS) significantly enhances sensitivity and enables single-molecular detection, quantification by this method is still challenging because of large signal fluctuations.

Structures of ions accommodated in salty ice Ih crystals.

Frozen aqueous electrolytes are ubiquitous and involved in various phenomena occurring in the natural environment. Although salts are expelled from ice during freezing of aqueous solutions, minor amounts of the constituent ions are accommodated in the crystal lattice of ice. This phenomenon was associated with the generation of the Workman-Reynolds freezing potential.

Directional Supramolecular Polymerization in a Dynamic Microsolution: A Linearly Moving Polymer's End Striking Monomers.

Although directional chain reactions are common in nature's self-assembly processes and in covalent polymerizations, it has been challenging to perform such processes in artificial one-dimensional self-assembling systems. In this paper, we describe a system, employing perylene bisimide (PBI) derivatives as monomers, for selectively activating one end of a supramolecular polymer during its growth and, thereby, realizing directional supramolecular polymerization. Upon introduction of a solution containing only a single PBI monomer into the microflow channel, nucleation was induced spontaneously.

Hydration of bromide at reverse micelle interfaces studied by X-ray absorption fine structure.

Nanoconfined water exhibits various interesting properties, which are not only of fundamental importance but also of practical use. Because reverse micelles (RMs) provide versatile ways to prepare nanoconfined water, the understanding of their physicochemical properties is essential for developing efficient applications. Although the water properties in the RMs could be affected by its interaction with the RM interface, the details have not been well understood.

Controlling water transport between micelles and aqueous microdroplets during sample enrichment.

Droplet microfluidics technologies have advanced rapidly, but enrichment in droplets has still been difficult. To deterministically control the droplet enrichment, the water transport from an aqueous microdroplet in organic continuous phase containing span 80 micelles was investigated. Organic phase containing Span-80-micelles contacted a NaCl aqueous solution to control hydration degree of the micelles, prior to being used in the microfluidic device.

Particle Manipulation with External Field; From Recent Advancement to Perspectives.

Physical forces, such as dielectric, magnetic, electric, optical, and acoustic force, provide useful principles for the manipulation of particles, which are impossible or difficult with other approaches. Microparticles, including polymer particles, liquid droplets, and biological cells, can be trapped at a particular position and are also transported to arbitrary locations in an appropriate external physical field. Since the force can be externally controlled by the field strength, we can evaluate physicochemical properties of particles from the shift of the particle location.

Multiphase Behavior of Tetraphenylethylene Derivatives with Different Polarities at High Pressures.

Although both pressure and temperature are essential parameters governing thermodynamics, the effects of the pressure on solution-phase equilibria have not been well studied compared to those of temperature. Here, we demonstrate the interesting pressure-dependent behavior of tetraphenylethylene (TPE) derivatives in multiphase systems composed of an organic phase and an aqueous phase in the presence and absence of γ-cyclodextrin (γ-CD). In this system, tetraphenylethylene monocarboxylic acid (TPE1H) and its dicarboxylic acid (TPE2H) are distributed in the aqueous phase and dissociated into the corresponding anions, that is, TPE1 and TPE2, when the pH is sufficiently high.

Reverse micelle chromatography for evaluation of partition of organic solutes to micellar pseudophases.

The evaluation of solute partition from an organic solvent to a reverse micelle (RM) is critical for designing effective reaction systems and for synthesizing functional materials using the nano water-phase in the RM. Although spectroscopic methods have been extensively employed for determining the partition constants of solutes in the RM systems, their applications are limited to the case, in which the background absorption is low and the spectroscopic features of the solute are effectively varied by its partitioning to RMs. This paper proposes a novel chromatographic method to overcome this limitation of conventional methods.

Ice Confinement-Induced Solubilization and Aggregation of Cyanonaphthol Revealed by Fluorescence Spectroscopy and Lifetime Measurements.

When an aqueous salt solution freezes, a freeze-concentrated solution (FCS) separates from the ice. The properties of the FCS may differ from those of a supercooled bulk solution of the same ionic strength at the same temperature. The fluorescence and lifetime characteristics of 6-cyano-2-naphthol (6CN) were studied in frozen NaCl solutions in order to provide insight into the solution properties of the FCS.

Interaction between antifreeze protein and ice crystal facet evaluated by ice-channel electrophoretic measurements of threshold electric field strength.

The chemical interaction between antifreeze proteins (AFPs) and ice crystals is evaluated via electrophoresis of AFP-anchored microparticles in fluidic channels formed in frozen aqueous sucrose. Straight fluidic channels are created in a flat glass chamber connecting two Ag/AgCl electrodes. This configuration allows us to estimate an electric field strength exerted on probe particles migrating along the channel.

Aptamer-Based Sensing of Small Organic Molecules by Measuring Levitation Coordinate of Single Microsphere in Combined Acoustic-Gravitational Field.

We present aptamer-based sensing using a coupled acoustic-gravitational (CAG) field, which transduces a change in the density of a microparticle (MP) to a change in the levitation coordinate. A large density of the MP is initially induced by the binding of gold nanoparticles (AuNPs) on the MP through sandwich hybridization with aptamer DNA molecules. Targets added to the system interact with the aptamer DNA molecules to form complexes, and the duplex between the aptamer and the probe DNA molecules is dissociated.

Space Size-Dependent Transformation of Tetraphenylethylene Carboxylate Aggregates by Ice Confinement.

Tetraphenylethylene carboxylate (TPEC) aggregates are transformed by ice confinement, which is controlled by the initial concentration of sucrose employed as a cryoprotectant and temperature. The freezing of aqueous sucrose leads to the formation of micro- or nanoliquid phase confined in ice. Aggregation-induced emission (AIE) of tetraphenylethylene carboxylate (TPEC) in the ice-confined space is explored using fluorescence spectroscopy and lifetime measurements.

Frozen Solution-Mediated Asymmetric Synthesis: Control of Enantiomeric Excess.

Asymmetric List-Mannich reactions were carried out in the frozen state to afford optically active adducts in moderate-to-good chemical yields and enantiomeric excesses (ee). The frozen solution exerts critical control of ee entropy changes, in sharp contrast to the enthalpy-driven asymmetric reactions typically observed in homogeneous solvents. This study provides new perspectives for asymmetric syntheses and an attractive alternative to conventional media.

Hydrostatic Pressure-Induced Spectral Variation of Reichardt's Dye: A Polarity/Pressure Dual Indicator.

The famous solvatochromic Reichardt's dye was applied to quantify hydrostatic pressure in media. The UV/vis spectra of the dye in various organic solvents are shifted bathochromically or hypsochromically at the shorter- or longer-wavelength band, respectively, upon hydrostatic pressurization. The value, determined by an absorption maximum, in ethyl acetate increases from 38.

Size-Tunable Micro-/Nanofluidic Channels Fabricated by Freezing Aqueous Sucrose.

Upon freezing aqueous sucrose at temperatures higher than the eutectic point (-14 °C in this case), two phases, that is, ice and freeze concentrated solution (FCS), are spontaneously separated. FCS forms through-pore fluidic channels when thin ice septum is prepared from aqueous sucrose. Total FCS volume depends on temperature but is independent of the initial sucrose concentration.

Multiple MicroRNA Quantification Based on Acoustic Levitation of Single Microspheres after One-Pot Sandwich Interparticle Hybridizations.

We propose a scheme for the sensitive quantification of multiple microRNAs (miRNAs) on the basis of the levitation coordinate change (Δ z) of single microparticles of different sizes in a coupled acoustic-gravitational (CAG) field. This field transduces the density change of a microparticle into Δ z, which can be measured with high precision. The density of a microparticle is induced by the binding of gold nanoparticles (AuNPs) on it through the sandwich DNA hybridization with miRNA.

Growth and Morphology of Liquid Phase in Frozen Aqueous NaCl Probed by Voltammetry and Simulations.

Cyclic voltammograms (CVs) of Fe(CN) are measured using a microelectrode in frozen aqueous NaCl solutions to obtain morphological information on the liquid phase developed on the electrode surface. CVs in frozen solutions feature the radial diffusion similar to that measured in bulk solution in some cases but the linear diffusion in other cases. The former suggests the sufficient growth of the liquid phase, whereas the latter implies the diffusion paths in particular directions are hindered.

Zeptomole Biosensing of DNA with Flexible Selectivity Based on Acoustic Levitation of a Single Microsphere Binding Gold Nanoparticles by Hybridization.

A novel scheme for DNA sensing at the zeptomole level is presented, based on the levitation of a single microsphere in a combined acoustic-gravitational (CAG) field. The levitation of a microsphere in the field is predominantly determined by its density. Capture and reporter probe DNAs are anchored on poly(methyl methacrylate) microsphere (PMMA) and gold nanoparticles (AuNPs), respectively, and a target DNA induces the binding of AuNPs on PMMA.

Zeta potential determination with a microchannel fabricated in solidified solvents.

This paper proposes a simple and versatile method for the determination of the zeta potential of a channel wall and discusses the values measured for the surface of frozen solvents, which are not only of scientific interest but also of potential use for microfluidic platforms. The zeta potential of the solid surface is an important parameter for discussing its electrokinetic properties, the distribution and reaction of ions in an electric double layer, and the fluidic behavior in the space surrounded by the surface. While the zeta potential of colloidal matters can be determined from their electrophoretic mobility, it is often difficult to determine that of a bulk material.

Electrophoresis in ice surface grooves for probing protein affinity to a specific plane of ice crystal.

Channel-like grooves are formed on the surface of frozen aqueous sucrose. They are filled with a freeze concentrated solution (FCS) and act as an efficient size-tunable separation field for micro and nanoparticles. The width of the channel can be easily varied by changing the temperature.