The blood vessels are important tissues that carry blood throughout the body and are associated with various diseases. Therefore, bioassays have been conducted using animal blood vessels and cells for the development of therapeutic agents and treatment methods. Many animal experiments have been conducted using mouse skin or chicken egg, and cell-based experiments have been conducted using vascular endothelial cells. In contrast, bioassays using biomimetic models based on microfluidic devices called Organ-on-a-Chip or Microphysiological Systems (MPS) have been attracting attention in recent years. Various bioassays have been developed, including permeability tests of vascular endothelial cells cultured on a porous membrane, chemotaxis tests under a concentration gradient of stimulant or oxygen, and tests related to angiogenesis in a hydrogel, and are expected to contribute to medical physiology research.

Quasi-elastic laser scattering (QELS) method is an optical scattering measurement technique by thermally excited capillary wave at gas / liquid and liquid / liquid interfaces. It can measure surface tension optically, which is a distinctive feature in micro-nano sciences. While conventional QELS method requires precise scattering-angle determination and light’s wavelength information for surface tension calculation, new QELS method utilizes spontaneous capillary wave resonance at spatially restricted interfaces in microchannels, microwells, and microdroplets, where the modes’ characteristics and their sizes are required for the tension. This paper provides an explanation of the principle of the method, demonstrats the measurements for gas / liquid interfaces in the microchannels, microwells, and microdroplets, and discusses the method’s usefulness for contemporary micro-nano sciences.

As a sensor for personalized medicine, single molecule electrical measurement using nanodevices is currently attracting attention because of its ability to comprehensively and simultaneously detect various target markers in the biological and medical fields. Nanodevices are integrated nanostructures such as nanopores, nanogaps, nanopipettes, and nanofluidic channels (nanochannels), which can be fabricated using microfabrication techniques. Combining these devices with a high-sensitivity current measurement system makes it possible to detect electricity in each molecule at the single-molecule level. This method is characterized by high sensitivity, low cost, high-throughput detection, portability, low cost through mass production technology, and the possibility of integrating various functions and multiple sensors. This paper, I focuses on medical applications of single molecule electrical measurement using such nanodevices, and discusses current applications of nanodevices in electrical measurement systems. Among them, I introduce a direct sensing method for biomolecules using nanogap devices and its detection of biomolecules, such as nucleic acid base chains, peptides, and signaling molecules. These technologies are expected to contribute to the realization of personalized medicine in the future. In addition, the current issues and future prospects of single molecule electrical measurement technology using nanodevices are discussed.

We have developed a system that can separate planktons and other microorganisms in a liquid according to their characteristics based on the electromagnetophoresis and microfluidic control. Rapid growth of planktons causes public health problems such as red tides and damage to the fishing industry, so a compact system that can immediately inspect the state of planktons on the spot is very effective in solving this problem. In this study, we developed a system that can separate microorganisms such as fine-grained phytoplankton by combining electromagnetophoresis, which occurs when a magnetic field and electric current are applied orthogonally to each other, and a microfluidic device, utilizing the phenomenon in which electromagnetophoresis force increases with particle size. The system is capable of characterizing microorganisms by measuring their migration distance and speed through image analysis. Using the developed system, we have demonstrated the possibility of highly efficient separation of microorganisms based on the migration distance and speed of each size particle in the range of 10 to 50 μm in diameter.

MicroRNAs (miRNAs) within extracellular vesicles (EVs) in body fluids may serve as biomarkers for low-invasive early diseases diagnostics. Although isolation of EVs in body fluids is a crucial step for analyzing miRNAs within the EVs, conventional techniques face challenges due to their low isolation efficiency and requirements of large sample volume. In this work, we propose a method for efficient EV isolation and in-situ miRNA extractions using a disposable microfluidic device with ZnO nanowires. The device has a microchannel on a polymer substrate and the ZnO nanowires are embedded inside the microchannel. The device allows for capturing EVs on nanowire surfaces from biological fluids and extracting miRNAs based on chemical lysis of the captured EVs. Two important factors for the efficient capture mechanism are large surface area of the nanowires and electrostatic interactions between the nanowires and EVs. Our demonstrations confirmed the device isolated EVs from 1 mL of cell supernatant and serum more efficiently in comparison to conventional ultracentrifugation and polymeric precipitation methods. Moreover, by using microarray-based detections of miRNAs extracted from the EVs in human serum, the device also presented a larger number of the detected miRNA types than the conventional methods. EV isolation and miRNA extractions using the device may contribute to realize low-invasive early disease diagnosis and new biomarker development.

Aptamers, which show properties of specific binding to their target molecules, are expected to become an alternative to antibodies for use as molecular recognition probes instead of antibodies. However, long and laborious selection procedures have hindered their application. To overcome the drawbacks, rapid and simple selection methods using a microscale electrophoretic filtration device have been developed. In the first study, the aptamers for immunoglobulin E were successfully selected by three cycle selection based on the developed method. To realize more rapid and simple selection, aptamer selection by single cycle procedure was demonstrated. It was confirmed that CD63 as a model target was successfully trapped by the capillary device partially plugged with a polyacrylamide hydrogel. A DNA library containing various sequences were then electrokinetically introduced into the device after trapping CD63, a large volume of DNAs bound with the trapped CD63. After washing and elution schemes, DNAs located in the eluents were enhanced by PCR, and then their sequences were analyzed by next generation sequencer. As a result, one of the obtained aptamer candidates shows similar motifs to the previously reported aptamer. Isothermal titration calorimetry verified the binding ability and specificity of the obtained candidate to CD63. Consequently, it was clarified that the developed method and device is applicable to the rapid and simple selection of aptamers using the single cycle procedure.

When a glass capillary with a nanopore at its tip is filled with a solution of low ion concentration, the ion concentration at the tip is higher than expected. This is because the ions form an electrical double layer inside the wall. In this case, the ion currents conducted via the nanopore differ dramatically depending on the polarity of the applied potential. This phenomenon is known as ion current rectification (ICR). ICR shows great potential for applications in bioassay methodology, as it is heavily influenced by the amount of surface charges on the inside wall of the nanopore, allowing it to be seamlessly applied in biosensing procedures. However, ICR can only be induced under low ion concentrations, preventing it from being applied for biosensing under physiological conditions. To address this issue, the effects of the ion concentration of phosphate buffer solutions (PBS) in a glass nanocapillary and bulk outside of the capillary on ICR were investigated in this study. Three ion concentrations were introduced into the capillary and the bulk, and ion current via the nanopore was measured. The results show that ICR was successfully monitored even though PBS of a physiological condition was used in either the glass nanocapillary or bulk. In addition, cell spheroids were monitored inside the capillary as a preliminary study for biosensing. This finding can be utilized for ICR-based biosensing applications under a physiological condition.

In recent years, there has been increasing demand for miniaturized analytical instruments that allow immediate on-site analysis. We have been developing a portable HPLC system consisting of a column-integrated chip and a compact, low-power electroosmotic flow pump. This study aims to extend the versatility of the portable HPLC system with a further reduction of the overall system size, and thus we constructed a UV absorbance detection module that can be mounted to the column-integrated chip. For this detection module, a UV light-emitting diode (peak wavelength = 255 nm) and photodiode were used as a light source and photodetector, and a system to control their operation and process the signals was also constructed. The developed detection module exhibited excellent performances as an HPLC detector.

In analysis using microfluidic devices, adsorption of samples and other substances on the channel walls can be a problem. Especially in immunoassays using polydimethylsiloxane (PDMS) devices, the adsorption of antibodies and other substances to be measured greatly affects measurement performance. In this study, we investigated the effect of the addition of two blocking agents on the detection sensitivity of okadaic acid (OA), a diarrheal shellfish poison, by fluorescence polarization immunoassay. In addition, the dissociation constants for the antibody and tracer were calculated from the obtained calibration curve.