Hirofumi Tani

Micelle-mediated extraction

The extraction technique based on phase separation in aqueous micellar solutions is reviewed. The technique has now been utilized for separation and preconcentration of metal chelates, organic compounds, and proteins. Additionally, the phase behavior of the micellar solutions and recent advances in the phase separation technique are also described. In the extraction of metal chelates, distribution equilibria are considered. In contrast to conventional solvent extraction, the distribution of metal chelates into a condensed surfactant phase (surfactant-rich phase) was dependent on metal ions. Proteins were extractable into the surfactant-rich phase according to their hydrophobicity. The recent use of affinity ligands and water-soluble polymers for controlling extractability of proteins are also introduced.

Phase separation in aqueous micellar solutions of nonionic surfactants for protein separation

Abstract The use of phase separation in aqueous micellar solutions of nonionic surfactants is introduced as a separation method for membrane proteins. Recent progress in phase separation is also described.

Advances in Microfluidic Paper-Based Analytical Devices for Food and Water Analysis

Food and water contamination cause safety and health concerns to both animals and humans. Conventional methods for monitoring food and water contamination are often laborious and require highly skilled technicians to perform the measurements, making the quest for developing simpler and cost-effective techniques for rapid monitoring incessant. Since the pioneering works of Whitesides’ group from 2007, interest has been strong in the development and application of microfluidic paper-based analytical devices (μPADs) for food and water analysis, which allow easy, rapid and cost-effective point-of-need screening of the targets. This paper reviews recently reported μPADs that incorporate different detection methods such as colorimetric, electrochemical, fluorescence, chemiluminescence, and electrochemiluminescence techniques for food and water analysis.

A strategy for synthesis of lipid nanoparticles using microfluidic devices with a mixer structure

Formation behavior of lipid nanoparticles (LNPs) in microfluidic devices with a staggered herringbone micromixer (SHM) structure was investigated. The fundamental role for SHMs in LNP formation was demonstrated by determining such factors as the limiting SHM cycle numbers and the effect of flow rate. The SHM cycle numbers and the position of the first SHM were as significant as factors as the flow rate condition for producing the small-size LNPs.

Polymer‐induced phase separation in aqueous micellar solutions of octyl‐β‐D‐thioglucoside for extraction of membrane proteins

A water-soluble polymer such as polyethylene glycol (PEG), Dextran T-500 (Dx), or diethylaminoethyl-Dextran (DEAE-Dx) induced aqueous micellar solutions of octyl-beta-D-thioglucoside (OTG) to phase separation at 0 degrees C. One of the two phases thus formed is a surfactant-depleted aqueous solution (aqueous phase) of a water-soluble polymer and the other a concentrated OTG solution (surfactant-rich phase). In a combination of OTG with PEG or Dx, cytochrome P450 (P450) and cytochrome b(5) (b(5)) were well extracted into the surfactant-rich phase. The extraction yield of P450 was slightly greater than that of b(5). In contrast to PEG and Dx, DEAE-Dx markedly reduced the extraction of b(5), while that of P450 remained almost unchanged. DEAE-Dx served the dual functions of inducing the phase separation and preventing the extraction of b(5) into the surfactant-rich phase. This depressed extraction of b(5) was reversed by the addition of potassium phosphate. DEAE-Dx and potassium phosphate proved effective in controlling the extractability of b(5). The polymer-induced phase separation provides a new basis for highly efficient extraction of membrane proteins under mild conditions that should be acceptable for thermolabile membrane proteins under physiological conditions.

Enhancement of the excluded-volume effect in protein extraction using triblock copolymer-based aqueous micellar two-phase systems

Abstract Triblock copolymer surfactants consisting of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), Pluronic L61 (PEO–PPO–PEO, L61) and Pluronic 25R2 (PPO–PEO–PPO, 25R2) were exploited in aqueous micellar two-phase systems for the protein extraction. The extraction was based on the phase separation into surfactant-depleted and -condensed phases (an aqueous and a surfactant-rich phases, respectively) upon warming aqueous micellar solutions of triblock copolymer. In both systems, hydrophilic proteins such as albumin were not extracted into the surfactant-rich phase. On the other hand, hydrophobic cytochrome b 5 was well extracted in the L61 system due to hydrophobic interaction. However, the extraction of cytochrome b 5 was not observed in the 25R2 system. This abnormal extractability of cytochrome b 5 in the 25R2 system was explained by the enhanced excluded-volume interaction between cytochrome b 5 and 25R2 micellar network in the surfactant-rich phase, which overcomes the hydrophobic interaction. Additionally, ionic surfactants were added into the systems for controlling extractability of proteins. In the 25R2 system, cationic tetradecyltrimethylammonium was effective for extracting anionic cytochrome b 5 against the excluded-volume effect, while not for anionic albumin because of its large molecular weight. In 25R2 system containing ionic surfactant, the partitioning of proteins were found to be governed by the hydrophobic, excluded-volume, and electrostatic interactions. Micellar network formed by 25R2 type of surfactant with a strong excluded-volume interaction could provide new selective extraction systems for the separation of proteins.

Image analysis for a microfluidic paper-based analytical device using the CIE L*a*b* color system

The combination of a microfluidic paper-based analytical device (μPAD) and digital image analysis is widely used for quantitative analysis with μPADs because of its easy and simple operation. Herein, we have demonstrated a quantitative analysis based on multiple color changes on a μPAD. The CIE L*a*b* color system was employed to analyse the digital images obtained with the μPAD. We made pH measurements using a universal pH-indicator showing multiple color changes for various pH values of aqueous test solutions. The detectable pH range of this method was wider than the typical grayscale-based image analysis, and we succeeded in the measurements for a wide pH range of 2-9.

Separation of microsomal cytochrome b5 via phase separation in a mixed solution of Triton X-114 and charged dextran

The successful introduction of a charged dextran into the Triton X-114 phase separation system for the selective extraction of cytochrome b5 (cyt. b5) in liver microsomes is described. In the absence of charged dextran, 55% of total microsomal proteins and 84% of cyt. b5 were extracted into the surfactant-rich phase. In the presence of anionic dextran sulfate, the extractability of total microsomal proteins was greatly reduced while that of cyt. b5 was increased. After triplicate extraction, cyt. b5 was purified more than 10-fold from microsomes with a recovery of 91% in the surfactant-rich phase. In view of its operational simplicity, this method provides a good means for the partial purification of cyt. b5 prior to chromatographic separations.

Fluorescence Polarization Measurement System Using a Liquid Crystal Layer and an Image Sensor

The detection system which enables simultaneous fluorescence polarization (FP) measurement of multiple samples was proposed and proven by a proof-of-concept experiment on the viscosity dependence of FP of fluorescein sample in water-ethylene glycol solution and another experiment on the FP immunoassay of prostaglandin E2 sample. The measurement principle of FP is based on the synchronization between the orientation of the liquid crystal molecules and the sampling frequency of a CCD. This report is the first description of the simultaneous FP measurement of multiple samples. This system has a great potential for equipment miniaturization and price reduction as well as providing simultaneous FP measurement of multiple samples.

A microfluidic-based protein crystallization method in 10 micrometer-sized crystallization space

Protein crystallization and subsequent X-ray diffraction analysis of the three-dimensional structure are necessary for elucidation of the biological functions of proteins and effective rational drug design. Therefore, controlling protein crystallization is important to obtain high resolution X-ray diffraction data. Here, a simple microfluidic method using chips with 10 and 50 μm high crystallization chambers to selectively form suitable single protein crystals for X-ray analysis is demonstrated. As proof of concept, three different types of proteins: lysozyme, glucokinase from Pseudoalteromonas sp. AS-131 (PsGK), and NADPH-cytochrome P450 oxidoreductase–heme oxygenase complex were crystallized. We demonstrate that the crystal growth orientation depends on the height of the crystallization chamber regardless of the protein type. Our results suggest that the confined micro space induces the protein molecules to adhere to a specific crystal face and affects the growth kinetics of each crystal face. The present microfluidic-based protein crystallization method can reform a suitable single protein crystal for X-ray analysis from aggregates of needle-shaped protein crystals.