Masatoshi Maeki

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.

Microfluidic Approaches for Protein Crystal Structure Analysis

This review summarizes two microfluidic-based protein crystallization methods, protein crystallization behavior in the microfluidic devices, and their applications for X-ray crystal structure analysis. Microfluidic devices provide many advantages for protein crystallography; they require small sample volumes, provide high-throughput screening, and allow control of the protein crystallization. A droplet-based protein crystallization method is a useful technique for high-throughput screening and the formation of a single crystal without any complicated device fabrication process. Well-based microfluidic platforms also enable effective protein crystallization. This review also summarizes the protein crystal growth behavior in microfluidic devices as, is known from viewpoints of theoretical and experimental approaches. Finally, we introduce applications of microfluidic devices for on-chip crystal structure analysis.

Elucidation of the physicochemical properties and potency of siRNA-loaded small-sized lipid nanoparticles for siRNA delivery

Because nanoparticles with diameters less than 50nm penetrate stromal-rich tumor tissues more efficiently, the synthesis of small-sized nanoparticles encapsulating short interfering RNA (siRNA) is important in terms of realizing novel siRNA medicine for the treatment of various cancers. Lipid nanoparticles (LNPs) are the leading systems for the delivery of siRNA in vivo. Limit size LNPs were successfully synthesized using a microfluidic mixing technique. However, the physicochemical properties and potential for in vivo siRNA delivery of the limit-size LNPs have not been examined in detail. In the present study, we prepared LNPs with different diameters from 32 to 67nm using a microfluidic mixing devise and examined the physicochemical properties of the particles and the potential for their use in delivering siRNA in vitro and in vivo to liver. Reducing the size of the LNPs causes poor-packing and an increased surface area, which result in their instability in serum. Moreover, it was revealed that the ability of endosomal escape (cytosolic siRNA release) of the smaller LNPs is subject to inhibition by serum compared to that of larger counterparts. Taken together, an increase in packing and avoiding the adsorption of serum components are key strategies for the development of next-generation highly potent and small-sized LNPs.

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.

Controlling one protein crystal growth by droplet-based microfluidic system

The preparation of a single crystal is important for a detailed understanding of the structure of protein. However, the preparation of a suitable crystal for X-ray diffraction is often a drawback due to the complexity of the protein molecules and the limited fundamental understanding of the protein crystallization mechanism. In this study, we studied the crystallization mechanism in droplet that was prepared by the microfluidic chip. We found that the mechanism of crystal growth in droplet is different from that by a conventional microbatch method. One crystal was grown in one droplet by controlling droplet shape and droplet volume. In addition, the surface area in droplet affected the size of the obtained protein crystal and the number of crystal(s). The growth of the (110) and (101) faces of tetragonal crystal could be determined by studying one crystal formed within one droplet, indicating that the observation and evaluation of one crystal growth kinetics is easily carried out compared with the conventional method.

Controlling Protein Crystal Nucleation by Droplet‐Based Microfluidics

Herein, we demonstrate the potential of droplet-based microfluidics for controlling protein crystallization and generating single-protein crystals. We estimated the critical droplet size for obtaining a single crystal within a microdroplet and investigated the crystallization of four model proteins to confirm the effect of protein molecular diffusion on crystallization. A single crystal was obtained in microdroplets smaller than the critical size by using droplet-based microfluidics. In the case of thaumatin crystallization, a single thaumatin crystal was obtained in a 200 μm droplet even with high supersaturation. In the case of ferritin crystallization, the nucleation profile of ferritin crystals had a wider distribution than the nucleation profiles of lysozyme, thaumatin, and glucose isomerase crystallization. We found that the droplet-based microfluidic approach was able to control the nucleation of a protein by providing control over the crystallization conditions and the droplet size, and that the diffusion of protein molecules is a significant factor in controlling the nucleation of protein crystals in droplet-based microfluidics.

A method for generating single crystals that rely on internal fluid dynamics of microdroplets

The single crystallization method by focusing on the characteristic internal fluid dynamics of the microdroplets was explored. Also the theoretical background was discussed, and the droplet size for obtaining only a single crystal within a microdroplet was estimated.

A method of cryoprotection for protein crystallography by using a microfluidic chip and its application for in situ X-ray diffraction measurements.

We demonstrate a seamless and contactless method from protein crystallization to X-ray analysis using a microfluidic chip with the aim of obtaining a complete crystallographic data set of a protein crystal under cryogenic conditions. Our microfluidics-based approach did not require direct manipulation of the protein crystal. Therefore, the microfluidic chip approach is suitable for novices of X-ray analysis of protein crystals. We also investigated the effect of stepwise cryoprotection on the quality of protein crystals. Protein crystals with cryoprotection via on-chip manipulation did not show deterioration of crystallographic quality of the protein crystal. The complete diffraction data set of a protein crystal, which is required for determining the 3D structure of the target protein, is obtainable by a simple manipulation.

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.

Advances in microfluidics for lipid nanoparticles and extracellular vesicles and applications in drug delivery systems

Abstract Lipid‐based nanobiomaterials as liposomes and lipid nanoparticles (LNPs) are the most widely used nanocarriers for drug delivery systems (DDSs). Extracellular vesicles (EVs) and exosomes are also expected to be applied as DDS nanocarriers. The performance of nanomedicines relies on their components such as lipids, targeting ligands, encapsulated DNA, encapsulated RNA, and drugs. Recently, the importance of the nanocarrier sizes smaller than 100 nm is attracting attention as a means to improve nanomedicine performance. Microfluidics and lab‐on‐a chip technologies make it possible to produce size‐controlled LNPs by a simple continuous flow process and to separate EVs from blood samples by using a surface marker, ligand, or electric charge or by making a mass or particle size discrimination. Here, we overview recent advances in microfluidic devices and techniques for liposomes, LNPs, and EVs and their applications for DDSs. Graphical abstract Figure. No Caption available.