Single particle/molecule tracking is widely used for the evaluation of diffusion coefficients using diverse tracking algorithms. Many of them require the subtle decision of displacement threshold parameter to enable the appropriate tracking, though it depends on both of the diffusion coefficient itself and the measurement system. A simple and highly transferable technique is proposed to overcome this difficulty based on the evaluation of diffusion coefficient from the peak position of the distribution of squared displacements in the logarithmic scale. In combination with its linear dependence on time, this protocol is remarkably robust against the too large value of the displacement threshold including that covers the whole image. Furthermore, the proposed technique is compatible with many of the existing algorithms by construction.

Industrial applications of cellulose nanofibres (CNFs) include the additive to a wide range of materials from display and cosmetic to pigment inks. Many of these expected applications are based on the mixture of colloidal particles and CNFs in aqueous dispersion. In particular, the mixed dispersion is typically processed in such a way that the droplet or shallow wide volume of dispersion is dried on the substrate or container. In this work, the basic physical properties that these diverse kinds of potential applications share in common are focused on. The colloidal films were fabricated consisting of polystyrene particles and CNFs under the condition of various concentration combinations through the drying of aqueous dispersion in polystyrene well plates. It has been found that the films fabricated from higher concentrations of CNF tend to peel-off spontaneously in the drying process. The basic mechanism of phenomenon is attributed to the contraction of CNFs during the drying by hydrogen bonding between the filaments.

Promising versatile applications of cellulose nanofibres (CNFs) include film structures for device substrates and surface coatings. Although there are various factors that affect the textures of such ‘nanopapers’, the drying from aqueous dispersion of CNF is the typical process to fabricate them. The basic property on this drying process is focused on, paying attention to the influence of temperature on the macroscopic uniformity. On the one hand, higher drying temperature is advantageous for the fast fabrication. On the other hand, too high temperature leads to significant nonuniformity, are focused on of the film. They propose that this drawback is suppressed by the multi-step coating process. The multi-step coating technique is simple without extra introduction of apparatus or chemical species. Therefore, it is a good option, e.g. when trying to fabricate relatively thin film structures where coffee-ring-like phenomena tend to take place.

Particles transport driven by a temperature gradient in a solution is known as thermophoresis or Soret effect. The drift velocity of a particle is expressed as , where is a thermophoretic mobility. Therefore, the thermophoretic mobility is a parameter to characterise the nature of thermophoresis, and the systematic measurement of for various combinations of particles and solvents is necessary for its potential application. In the present work, we develop the microfluidic system called microgap Soret cell and show its validity by obtaining for wide experimental conditions. It is shown that the microgap Soret cell can rapidly and directly obtain the thermophoretic mobility of a particle with the diameter of by maintaining the large temperature gradient in the microfluidic system. Moreover, by using the microgap Soret cell, the temperature dependency of is investigated for thermophoresis of polystyrene particles in solutions of sodium hydroxide, polyethylene glycol, and glycerol.

Molecular transport technology is one of the hottest topics in micro- and nanofluidics. Target molecules are often transported by electric forces, e.g. capillary electrophoresis (EP), gel EP, biological and artificial nanopores. On the other hand, such methods are sometimes disturbed by surrounding environments because the surface effects tend to be prominent. The surface charges on the channel walls cause peculiar liquid flows in micro- and nanochannels. Thus, the isolation of electrophoretic transport from the fluidic effects is important to achieve the precise control of targets in confined spaces. In this study, a novel technique to control the transport of microparticles is proposed, where a liquid flow is involved by applying electric body forces. The direction of electrically charged microparticles is controlled by the electric forces not only on the particle but also in the liquid. Herein, an electrohydrodynamic flow is applied by preparing electrically polarised solutions. In this setup, the transport direction of particles can be changed depending on the electric forces by excessive ions, which is estimated by measuring electric conductivity.

Here, the voltage and current conditions required to form a nanoparticle chain bridging a gap between electrodes that is several tens of micrometres wide have been examined. When a voltage is applied to a gap between electrodes covered with a dispersion of nanoparticles, the nanoparticles are trapped in the gap by dielectrophoresis, forming a nanoparticle chain. It has been considered that a nanoparticle chain is formed in a gap only when a voltage higher than a certain value with a current lower than a certain value is applied to the gap. In this work, certain voltages were first applied with changing current to a 10 µm-wide gap between electrodes covered with a dispersion of 150 nm-diameter gold nanoparticles, and they found that a nanoparticle chain was formed only when 6.1 V_rms or more with 15 mA_rms or less was applied. Next, the process of nanoparticle chain formation in a 10 µm-wide gap was directly observed with high-magnification and high-speed microscopy, and they clarified the behaviour of nanoparticle chain formation when a low voltage, high voltage with high current, and high voltage with low current were applied. Finally, they measured the critical value of current for nanoparticle chain formation in a gap several tens of micrometres wide.

Monodisperse gold nanoparticles (GNPs) in aqueous dispersion were synthesised using a low-cost glass microfluidic device with a Y-shaped microchannel. The effects of channel width and flow rate on the size distribution of the synthesised GNPs were investigated. An aqueous solution of tetrachloroauric (III) acid (source of Au ions), and a mixture of an aqueous solution of sodium citrate acid (reducing agent) and tannic acid (protective agent), were injected into a microchannel in the microfluidic device by using a syringe pump. The absorption spectra at low flow rates showed sharper peaks in comparison with those at high flow rates. At the channel width of 260 μm, the full width at half maximum of the absorption peak was 79.2 nm for 0.05 ml/min and 92.9 nm for 0.06 ml/min. From transmission electron microscopy images, the GNPs synthesised using a channel width of 260 μm and flow rate of 0.05 ml/min were found to have a mean diameter of 11.5 nm and coefficient of variation of 0.09. These results confirmed that the combination of a low-flow rate and a small channel width is essential to obtain monodisperse GNPs.

In this work, micropillar array structures with overhang roofs which increase the switching range of the TiO₂ photoresponsive wettability, have been fabricated. The liquid droplet placed on the micropillar array exhibits the Cassie–Baxter superhydrophobic state because of the receding of the liquid–air interface to the pillar top, when its contact angle (θ _TiO2) on the TiO₂ surface exceeds than the geometrical angle (ψ) between the overhang roof and the vertical micropillar shaft. The Cassie–Baxter state can be transformed into the Wenzel state at a relatively large surface area of the micropillar array when the magnitude of θ _TiO2 becomes smaller than ψ after ultraviolet irradiation due to the photoinduced superhydrophilicity of TiO₂. The rutile TiO₂-coated micropillar array with a small ψ exhibits faster reverse wettability transformation from the Wenzel state to the Cassie–Baxter state despite the relatively small θ _TiO2 increase in the dark. In addition, the wettability reversal time was shortened from 180 to 6 min after decreasing ψ from 51° to 9°.

This work reports on the creation of an electroencephalogram (EEG) index and the discovery of a power ratio related to alpha band frequencies (8–13 Hz) that were experimentally found to have a high correlation with human mental fatigue. The EEG was measured from occipital lobe of the human brain by microfabricated dry candle-like microneedle electrodes (CMEs) that can avoid hairs and penetrate through the high-impedance stratum corneum. The newly identified EEG index exhibited higher correlations to mental fatigue states, which were rated subjectively via the visual analogue scale (VAS), than did heart rate variance, which is often used as the objective measure of fatigue levels. Interestingly, it was found that the index trend changed 10 min before the VAS did, which implies that the index could assess the onset of mental fatigue even before the subjects recognised it themselves. The identification of this EEG index, along with the ease of obtaining EEG measurements via CME, which is due to the fact that the CME does not require any skin preparation or conductive gels and can acquire EEGs from hair-covered parts of the scalp, can be expected to promote practical fatigue assessment applications that use EEGs.

The authors examined a shape of sample on micro-volume, which is a several μL, nuclear magnetic resonance (NMR) spectroscopy in order to obtain uniformed magnetic flux density in the sample and a sharp NMR spectrum by using a conventional NMR apparatus. Firstly, they simulated the magnetic flux density distribution in spherical and cubic shaped samples and calculated NMR spectra from each shape. The simulated NMR spectra from spherical samples were sharp enough, being <0.1 ppb in a full width at half maximum (FWHM). On the other hand, the simulated NMR spectra from cubic samples were much broader than those from spherical samples. Then, they made polydimethylsiloxane sample chambers with spherical or cubic sample of several µL in volume and they evaluated NMR spectra from those micro-volume sample chambers. As a result, they obtained a sharp NMR spectrum with FWHM of 2 ppb from the sample chamber with the spherical sample, and a broad spectrum with FWHM of 220 ppb from the sample chamber with the cubic sample. These results indicate that the spherical shape is essential to obtain a shape spectrum in micro-volume NMR spectroscopy by using a conventional NMR apparatus.

Death from overwork and severe accidents caused by mental fatigue and sleepiness are becoming one of the more pressing social problems of developed countries. Such mental fatigue and sleepiness often comes from declines and/or changes in wakefulness in our daily life. Recently, numerous researchers have focused on possible ways of utilising physiological signals to deduce alertness; however, the characteristic behaviours that can be used to deduce wakefulness are difficult to measure. To better understand the indices of change in wakefulness states, the authors fabricated a micro-optical sensor system that can measure physiological signals from eye and eyelid conditions without imposing stress on the user. Using the newly fabricated micro-optical sensor system, they have found and reproduced characteristic blink behaviours that are indicative of changes in a person's wakefulness. Herein, new indices are proposed that have potential for use in fatigue evaluation tests. The experimental results demonstrate that the sensor system can detect declines in and/or changes in wakefulness that indicate mental fatigue and sleepiness.

Inverting glasses invert the wearer's visual field in the vertical or horizontal direction using total internal reflection by triangular prisms. Inverting glasses are powerful tools for investigating neural adaptation and are widely used in the fields of psychology and brain science. However, conventional inverting glasses are not equipped with a detection system for eye movement or the line-of-sight of the wearer during experiments. Inverting glasses were developed that can be mounted with a see-through eye detection system, which consists of micropatterned dye-sensitised photovoltaic cells that determine the position of the pupil by detecting light reflected from the black and white parts of the eye. The detector does not require an external camera and is thus lightweight and has low-power consumption, which is advantageous for mounting on the inverting glasses. Using the developed inverting glasses, which swap the left and right visual fields, they conducted tracking and pointing tasks while measuring eye movement. Gaze learning curves were obtained from the experiments for the first time, which they believe will provide new and useful information to the study of neural adaptation.

Endoscopic palpation is a promising technology for detecting tumours that are too small to be detected by CT and magnetic resonance imaging, are not located on tissue surfaces, and cannot be observed using endoscopes. This method uses a small force sensor mounted on the tip of an endoscope. It is desirable that the sensor can scan tissue surfaces and continuously measure the stiffness of organs. Prior work developed a ballpoint-pen-like capacitive force sensor and carried out proof of principle experiments; however, the sensor was too large to be mounted on an endoscope. This study designed three-dimensional (3D) microfluidic channels encapsulating liquid metal to develop a sensor that is small enough to be mounted on an endoscope. Eight polydimethyl siloxane layers with channel structures were assembled and filled with Galinstan, a commercial liquid metal, to form 3D electrodes. The sensor was experimentally characterised and verified to be applicable to endoscopic palpation.

A cantilever-type vibration energy harvester (VEH) made of PolyVinylidene DiFluoride (PVDF) was fabricated and characterised. PVDF is one of polymer piezoelectric material, which is more flexible than ceramic-based piezoelectric materials such as lead zirconate titanate. Since PVDF dissolves in organic solvent, it is coatable on substrate or parts, making it compatible with micro electro mechanical systems process. The fabrication process of VEH is as follows: a PVDF film (thickness: 30 µm) was coated on a phosphor bronze rectangular plate (length: 35 mm, width: 15 mm, thickness: 0.1 mm) by bar-coating method, followed by polarisation by corona discharge method. Aluminium top electrode (length: 30 mm, width: 10 mm, thickness: 0.3 μm) was deposited on the PVDF film by DC sputtering. One end of the plate was clamped by a fixture to form a cantilever, the length of which is 25 mm. Finally, a proof mass (m = 0.2 g) was attached to the free end of cantilever. Output power P at resonant frequency (= 55 Hz) was measured as a function of load resistance R, in which acceleration was set to 17 m/s². Maximum output of 4.3 µW was achieved at R = 2.1 MΩ, which is not inferior to those of reported VEHs using ceramic piezoelectric materials.

This work describes a water surface mobile robot utilising surface tension forces. Recent biological studies on water striders revealed how they stay afloat and move on the surface of water. By using their hairy legs coated with hydrophobic substance produced, they increase the water repellency and float by the surface tension. This work focuses on understanding the static and dynamic interactions between supporting legs and the surface of water. First, microstructured wire legs were fabricated by using femtosecond laser machining to enhance the water repellency. Then the supporting force, the pull-off force and the drag force were measured to find the suitable legs for water strider robot. Finally, by assembling the legs optimised for supporting load and propulsion, a water strider robot weighing 4.39 g was developed. The robot successfully moved on the surface of water at a speed of 59.2 mm/s.