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Micromachines, Volume 10, Issue 2 (February 2019)

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Cover Story (view full-size image) Digital microfluidic chips (DMFs) manipulate droplets on the surface of electrode arrays coated [...] Read more.
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Open AccessArticle Design of a Micromachined Z-axis Tunneling Magnetoresistive Accelerometer with Electrostatic Force Feedback
Micromachines 2019, 10(2), 158; https://doi.org/10.3390/mi10020158
Received: 22 January 2019 / Revised: 21 February 2019 / Accepted: 21 February 2019 / Published: 25 February 2019
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Abstract
This paper presents the design, simulation, fabrication and experiments of a micromachined z-axis tunneling magnetoresistive accelerometer with electrostatic force feedback. The tunneling magnetoresistive accelerometer consists of two upper differential tunneling magnetoresistive sensors, a middle plane main structure with permanent magnetic films and lower [...] Read more.
This paper presents the design, simulation, fabrication and experiments of a micromachined z-axis tunneling magnetoresistive accelerometer with electrostatic force feedback. The tunneling magnetoresistive accelerometer consists of two upper differential tunneling magnetoresistive sensors, a middle plane main structure with permanent magnetic films and lower electrostatic feedback electrodes. A pair of lever-driven differential proof masses in the middle plane main structure is used for sensitiveness to acceleration and closed-loop feedback control. The tunneling magnetoresistive effect with high sensitivity is adopted to measure magnetic field variation caused by input acceleration. The structural mode and mass ratio between inner and outer proof masses are optimized by the Ansys simulation. Simultaneously, the magnetic field characteristic simulation is implemented to analyze the effect of the location of tunneling magnetoresistive sensors, magnetic field intensity, and the dimension of permanent magnetic film on magnetic field sensitivity, which is beneficial for the achievement of maximum sensitivity. The micromachined z-axis tunneling magnetoresistive accelerometer fabricated by the standard deep dry silicon on glass (DDSOG) process has a device dimension of 6400 μm (length) × 6400 μm (width) × 120 μm (height). The experimental results demonstrate the prototype has a maximal sensitivity of 8.85 mV/g along the z-axis sensitive direction under the gap of 1 mm. Simultaneously, Allan variance analysis illustrate that a noise floor of 86.2 μg/Hz0.5 is implemented in the z-axis tunneling magnetoresistive accelerometer. Full article
(This article belongs to the Special Issue MEMS/NEMS Sensors: Fabrication and Application)
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Open AccessArticle Design and Fabrication of a Wavelength-Selective Near-Infrared Metasurface Emitter for a Thermophotovoltaic System
Micromachines 2019, 10(2), 157; https://doi.org/10.3390/mi10020157
Received: 30 November 2018 / Revised: 20 February 2019 / Accepted: 22 February 2019 / Published: 25 February 2019
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Abstract
In this study, a tungsten-SiO2-based metal–insulator–metal-structured metasurface for the thermal emitter of the thermophotovoltaic system was designed and fabricated. The proposed emitter was fabricated by applying the photolithography method. The fabricated emitter has high emissivity in the visible to near-infrared region [...] Read more.
In this study, a tungsten-SiO2-based metal–insulator–metal-structured metasurface for the thermal emitter of the thermophotovoltaic system was designed and fabricated. The proposed emitter was fabricated by applying the photolithography method. The fabricated emitter has high emissivity in the visible to near-infrared region and shows excellent wavelength selectivity. This spectral emissivity tendency agreed well with the result calculated by the finite-difference time-domain method. Additionally, the underlying mechanism of its emission was scrutinized. Study of the fabrication process and theoretical mechanisms of the emission, clarified in this research, will be fundamental to design the wavelength-selective thermal emitter. Full article
(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)
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Open AccessArticle Multinucleation of Incubated Cells and Their Morphological Differences Compared to Mononuclear Cells
Micromachines 2019, 10(2), 156; https://doi.org/10.3390/mi10020156
Received: 29 January 2019 / Revised: 19 February 2019 / Accepted: 22 February 2019 / Published: 25 February 2019
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Abstract
Some cells cultured in vitro have multiple nuclei. Since cultured cells are used in various fields of science, including tissue engineering, the nature of the multinucleated cells must be determined. However, multinucleated cells are not frequently observed. In this study, a method to [...] Read more.
Some cells cultured in vitro have multiple nuclei. Since cultured cells are used in various fields of science, including tissue engineering, the nature of the multinucleated cells must be determined. However, multinucleated cells are not frequently observed. In this study, a method to efficiently obtain multinucleated cells was established and their morphological properties were investigated. Initially, we established conditions to quickly and easily generate multinucleated cells by seeding a Xenopus tadpole epithelium tissue-derived cell line (XTC-YF) on less and more hydrophilic dishes, and incubating the cultures with medium supplemented with or without Y-27632—a ROCK inhibitor—to reduce cell contractility. Notably, 88% of the cells cultured on a less hydrophilic dish in medium supplemented with Y-27632 became multinucleate 48 h after seeding, whereas less than 5% of cells cultured under other conditions exhibited this morphology. Some cells showed an odd number (three and five) of cell nuclei 72 h after seeding. Multinucleated cells displayed a significantly smaller nuclear area, larger cell area, and smaller nuclear circularity. As changes in the morphology of the cells correlated with their functions, the proposed method would help researchers understand the functions of multinucleated cells. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Blood Analysis)
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Open AccessArticle Interactive Effects of Rarefaction and Surface Roughness on Aerodynamic Lubrication of Microbearings
Micromachines 2019, 10(2), 155; https://doi.org/10.3390/mi10020155
Received: 30 January 2019 / Revised: 18 February 2019 / Accepted: 22 February 2019 / Published: 25 February 2019
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Abstract
The aerodynamic lubrication performance of gas microbearing has a particularly critical impact on the stability of the bearing-rotor system in micromachines. Based on the Duwensee’s slip correction model and the fractal geometry theory, the interactive effects of gas rarefaction and surface roughness on [...] Read more.
The aerodynamic lubrication performance of gas microbearing has a particularly critical impact on the stability of the bearing-rotor system in micromachines. Based on the Duwensee’s slip correction model and the fractal geometry theory, the interactive effects of gas rarefaction and surface roughness on the static and dynamic characteristics were investigated under various operation conditions and structure parameters. The modified Reynolds equation, which governs the gas film pressure distribution in rough bearing, is solved by employing the partial derivative method. The results show that high values of the eccentricity ratio and bearing number tend to increase the principal stiffness coefficients significantly, and the fractal roughness surface considerably affects the ultra-thin film damping characteristics compared to smooth surface bearing. Full article
(This article belongs to the Special Issue Gas Flows in Microsystems)
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Open AccessArticle Size Distribution Analysis with On-Chip Multi-Imaging Cell Sorter for Unlabeled Identification of Circulating Tumor Cells in Blood
Micromachines 2019, 10(2), 154; https://doi.org/10.3390/mi10020154
Received: 6 November 2018 / Revised: 13 December 2018 / Accepted: 20 December 2018 / Published: 25 February 2019
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We report a change of the imaging biomarker distribution of circulating tumor cell (CTC) clusters in blood over time using an on-chip multi-imaging flow cytometry system, which can obtain morphometric parameters of cells and those clusters, such as cell number, perimeter, total cross-sectional [...] Read more.
We report a change of the imaging biomarker distribution of circulating tumor cell (CTC) clusters in blood over time using an on-chip multi-imaging flow cytometry system, which can obtain morphometric parameters of cells and those clusters, such as cell number, perimeter, total cross-sectional area, aspect ratio, number of nuclei, and size of nuclei, as “imaging biomarkers”. Both bright-field (BF) and fluorescent (FL) images were acquired at 200 frames per second and analyzed within the intervals for real-time cell sorting. A green fluorescent protein-transfected prostate cancer cell line (MAT-LyLu-GFP) was implanted into Copenhagen rats, and the blood samples of these rats were collected 2 to 11 days later and measured using the system. The results showed that cells having BF area of 90 μm2 or larger increased in number seven days after the cancer cell implantation, which was specifically detected as a shift of the cell size distribution for blood samples of implanted rats, in comparison with that for control blood. All cells with BF area of 150 μm2 or larger were arranged in cell clusters composed of at least two cells, as confirmed by FL nucleus number and area measurements, and they constituted more than 1% of all white blood cells. These results indicate that the mapping of cell size distribution is useful for identifying an increase of irregular cells such as cell clusters in blood, and show that CTC clusters become more abundant in blood over time after malignant tumor formation. The results also reveal that a blood sample of only 50 μL is sufficient to acquire a stable size distribution map of all blood cells to predict the presence of CTC clusters. Full article
(This article belongs to the Special Issue State-of-the-Art Lab-on-a-Chip Technology in Japan)
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Open AccessArticle Design of a Dual-Technology Fusion Sensor Chip with a Ring Electrode for Biosensing Application
Micromachines 2019, 10(2), 153; https://doi.org/10.3390/mi10020153
Received: 29 January 2019 / Revised: 15 February 2019 / Accepted: 18 February 2019 / Published: 23 February 2019
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Quartz crystal microbalance (QCM) is still a new high-precision surface detection technique. However, the adsorption quality detected by the QCM currently contains a solvent-coupling quality and cannot separate the actual biomolecular mass. Local surface plasmon resonance (LSPR) can detect the mass of biomolecules, [...] Read more.
Quartz crystal microbalance (QCM) is still a new high-precision surface detection technique. However, the adsorption quality detected by the QCM currently contains a solvent-coupling quality and cannot separate the actual biomolecular mass. Local surface plasmon resonance (LSPR) can detect the mass of biomolecules, but requires a certain contrast between the solvent of the surrounding medium and the refractive index of the adsorbed layer. The sensor chip, combining two compatible technologies, can realize the simultaneous detection of biomolecules and improve the refractive index sensitivity. The structure of our chip is to prepare the ring-shaped gold electrode on the upper surface of the quartz crystal, the circular gold electrode on the bottom surface, and the spherical gold nanoparticles arrays in the center region of the ring electrode to form a QCM/LSPR dual-technology chip. Through simulation, we finally get the size of the best energy trap by the two electrodes on the upper surface and the lower surface: the ring-top electrode with a thickness of 100 nm, an inner diameter of 4 mm, and an outer diameter of 8 mm; and the bottom electrode with a thickness of 100 nm and a radius of 6 mm. By comparing the refractive index sensitivity, we chose a spherical gold nanoparticle with a radius of 30 nm and a refractive sensitivity of 61.34 nm/RIU to design the LSPR sensor chip. Full article
(This article belongs to the Special Issue Electronic Devices for Biomedical Applications)
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Open AccessReview Advances in Capacitive Micromachined Ultrasonic Transducers
Micromachines 2019, 10(2), 152; https://doi.org/10.3390/mi10020152
Received: 15 January 2019 / Revised: 13 February 2019 / Accepted: 18 February 2019 / Published: 23 February 2019
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Abstract
Capacitive micromachined ultrasonic transducer (CMUT) technology has enjoyed rapid development in the last decade. Advancements both in fabrication and integration, coupled with improved modelling, has enabled CMUTs to make their way into mainstream ultrasound imaging systems and find commercial success. In this review [...] Read more.
Capacitive micromachined ultrasonic transducer (CMUT) technology has enjoyed rapid development in the last decade. Advancements both in fabrication and integration, coupled with improved modelling, has enabled CMUTs to make their way into mainstream ultrasound imaging systems and find commercial success. In this review paper, we touch upon recent advancements in CMUT technology at all levels of abstraction; modeling, fabrication, integration, and applications. Regarding applications, we discuss future trends for CMUTs and their impact within the broad field of biomedical imaging. Full article
(This article belongs to the Special Issue MEMS Technology for Biomedical Imaging Applications)
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Open AccessArticle Tunable Memristic Characteristics Based on Graphene Oxide Charge-Trap Memory
Micromachines 2019, 10(2), 151; https://doi.org/10.3390/mi10020151
Received: 15 January 2019 / Revised: 3 February 2019 / Accepted: 22 February 2019 / Published: 23 February 2019
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Abstract
Solution-processable nonvolatile memory devices, consisted of graphene oxide (GO) embedded into an insulating polymer polymethyl methacrylate (PMMA), were manufactured. By varying the GO content in PMMA nanocomposite films, the memristic conductance behavior of the Ni/PMMA:GO/Indium tin oxide (ITO) sandwiched structure can be tuned [...] Read more.
Solution-processable nonvolatile memory devices, consisted of graphene oxide (GO) embedded into an insulating polymer polymethyl methacrylate (PMMA), were manufactured. By varying the GO content in PMMA nanocomposite films, the memristic conductance behavior of the Ni/PMMA:GO/Indium tin oxide (ITO) sandwiched structure can be tuned in a controllable manner. An investigation was made on the memristic performance mechanism regarding GO charge-trap memory; these blends were further characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), Fourier transform infrared spectra (FTIR), Raman spectra, thermogravimetric analysis, X-ray diffraction (XRD), ultraviolet-visible spectroscopy, and fluorescence spectra in particular. Dependent on the GO content, the resistive switching was originated from the charges trapped in GO, for which bipolar tunable memristic behaviors were observed. PMMA:GO composites possess an ideal capability for large area device applications with the benefits of superior electronic properties and easy chemical modification. Full article
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Open AccessArticle Analysis of Kerr Noise in Angular-Rate Sensing Based on Mode Splitting in a Whispering-Gallery-Mode Microresonator
Micromachines 2019, 10(2), 150; https://doi.org/10.3390/mi10020150
Received: 24 January 2019 / Revised: 14 February 2019 / Accepted: 20 February 2019 / Published: 23 February 2019
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Whispering-gallery-mode (WGM) microresonators have shown their potential in high-precision gyroscopes because of their small volume and high-quality factors. However, Kerr noise can always be the limit of accuracy. Angular-rate sensing based on mode splitting treats backscattering as a measured signal, which can induce [...] Read more.
Whispering-gallery-mode (WGM) microresonators have shown their potential in high-precision gyroscopes because of their small volume and high-quality factors. However, Kerr noise can always be the limit of accuracy. Angular-rate sensing based on mode splitting treats backscattering as a measured signal, which can induce mode splitting, while it is considered as a main source of noise in conventional resonator optical gyroscopes. Meanwhile, mode splitting also provides superior noise suppression owing to its self-reference scheme. Kerr noise in this scheme has not been defined and solved yet. Here, the mechanism of the Kerr noise in the measurement is analyzed and the mathematical expressions are derived, indicating the relationship between the Kerr noise and the output of the system. The influence caused by Kerr noise on the output is simulated and discussed. Simulations show that the deviation of the splitting caused by Kerr noise is 1.913 × 10−5 Hz at an angular rate of 5 × 106 °/s and the corresponding deviation of the angular rate is 9.26 × 10−9 °/s. It has been proven that angular-rate sensing based on mode splitting offers good suppression of Kerr noise. Full article
(This article belongs to the Special Issue MEMS Accelerometers)
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Open AccessArticle The Improvement on the Performance of DMD Hadamard Transform Near-Infrared Spectrometer by Double Filter Strategy and a New Hadamard Mask
Micromachines 2019, 10(2), 149; https://doi.org/10.3390/mi10020149
Received: 7 December 2018 / Revised: 15 February 2019 / Accepted: 15 February 2019 / Published: 23 February 2019
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Abstract
In the Hadamard transform (HT) near-infrared (NIR) spectrometer, there are defects that can create a nonuniform distribution of spectral energy, significantly influencing the absorbance of the whole spectrum, generating stray light, and making the signal-to-noise ratio (SNR) of the spectrum inconsistent. To address [...] Read more.
In the Hadamard transform (HT) near-infrared (NIR) spectrometer, there are defects that can create a nonuniform distribution of spectral energy, significantly influencing the absorbance of the whole spectrum, generating stray light, and making the signal-to-noise ratio (SNR) of the spectrum inconsistent. To address this issue and improve the performance of the digital micromirror device (DMD) Hadamard transform near-infrared spectrometer, a split waveband scan mode is proposed to mitigate the impact of the stray light, and a new Hadamard mask of variable-width stripes is put forward to improve the SNR of the spectrometer. The results of the simulations and experiments indicate that by the new scan mode and Hadamard mask, the influence of stray light is restrained and reduced. In addition, the SNR of the spectrometer also is increased. Full article
(This article belongs to the Special Issue Optical MEMS)
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Open AccessArticle In Situ Image Acquisition and Measurement of Microdroplets Based on Delay Triggering
Micromachines 2019, 10(2), 148; https://doi.org/10.3390/mi10020148
Received: 19 January 2019 / Revised: 14 February 2019 / Accepted: 20 February 2019 / Published: 22 February 2019
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Abstract
An in situ image acquisition apparatus based on delay triggering for visualizing microdroplets formation is described. The imaging system includes a charge-coupled device camera, a motion control card, a driving circuit, a time delay triggering circuit, and a light source. By adjusting the [...] Read more.
An in situ image acquisition apparatus based on delay triggering for visualizing microdroplets formation is described. The imaging system includes a charge-coupled device camera, a motion control card, a driving circuit, a time delay triggering circuit, and a light source. By adjusting the varying trigger delay time which is synchronized with respect to the signal for jetting, the steady sequential images of the droplet flying in free space can be captured real-time by the system. Several image processing steps are taken to measure the diameters and coordinates of the droplets. Also, the jetting speeds can be calculated according to the delay time interval. For glycerin/water (60:40, mass ratio), under the given conditions of the self-made pneumatically diaphragm-driven drop-on-demand inkjet apparatus, the average of diameter and volume are measured as 266.8 μm and 9944 pL, respectively, and the maximum average velocity of the microdroplets is 0.689 m/s. Finally, the imaging system is applied to measure the volume of 200 microsolder balls generated from the inkjet apparatus. The average diameter is 87.96 μm, and the relative standard deviation is 0.83%. The results show good reproducibility. Unlike previous stroboscopic techniques, the present in situ imaging system which is absence of instantaneous high intensity light employs two control signals to stimulate the microdroplet generator and the charge-coupled device (CCD) camera. Hence, the system can avoid the desynchronization problem of signals which control the strobe light-emitting diode (LED) light source and the camera in previous equipment. This technology is a reliable and cost-effective approach for capturing and measuring microdroplets. Full article
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Open AccessArticle Experimental Investigation on Direct Micro Milling of Cemented Carbide
Micromachines 2019, 10(2), 147; https://doi.org/10.3390/mi10020147
Received: 14 January 2019 / Revised: 19 February 2019 / Accepted: 19 February 2019 / Published: 22 February 2019
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Abstract
Cemented carbide is currently used for various precise molds and wear resistant parts. However, the machining of cemented carbide still is a difficult challenge due to its superior mechanical properties. In this paper, an experimental study was conducted on direct micro milling of [...] Read more.
Cemented carbide is currently used for various precise molds and wear resistant parts. However, the machining of cemented carbide still is a difficult challenge due to its superior mechanical properties. In this paper, an experimental study was conducted on direct micro milling of cemented carbide with a polycrystalline diamond (PCD) micro end mill. The cutting force characteristics, surface formation, and tool wear mechanisms were systematically investigated. Experimental results show that cemented carbide can be removed with ductile cutting utilizing the PCD tool with a large tool tip radius. Micro burrs, brittle pits, and cracks are the observed surface damage mechanisms. The tool wear process presents microchipping on the cutting edge and exfoliating on the rake face in the early stage, and then severe abrasive and adhesive wear on the bottom face in the following stage. Full article
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Open AccessArticle Investigation of Micromachined Antenna Substrates Operating at 5 GHz for RF Energy Harvesting Applications
Micromachines 2019, 10(2), 146; https://doi.org/10.3390/mi10020146
Received: 29 November 2018 / Revised: 18 January 2019 / Accepted: 18 January 2019 / Published: 22 February 2019
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This paper investigates micromachined antenna performance operating at 5 GHz for radio frequency (RF) energy harvesting applications by comparing different substrate materials and fabrication modes. The research aims to discover appropriate antenna designs that can be integrated with the rectifier circuit and fabricated [...] Read more.
This paper investigates micromachined antenna performance operating at 5 GHz for radio frequency (RF) energy harvesting applications by comparing different substrate materials and fabrication modes. The research aims to discover appropriate antenna designs that can be integrated with the rectifier circuit and fabricated in a CMOS (Complementary Metal-Oxide Semiconductor)-compatible process approach. Therefore, the investigation involves the comparison of three different micromachined antenna substrate materials, including micromachined Si surface, micromachined Si bulk with air gaps, and micromachined glass-surface antenna, as well as conventional RT/Duroid-5880 (Rogers Corp., Chandler, AZ, USA)-based antenna as the reference. The characteristics of the antennas have been analysed using CST-MWS (CST MICROWAVE STUDIO®—High Frequency EM Simulation Tool). The results show that the Si-surface micromachined antenna does not meet the parameter requirement for RF antenna specification. However, by creating an air gap on the Si substrate using a micro-electromechanical system (MEMS) process, the antenna performance could be improved. On the other hand, the glass-based antenna presents a good S11 parameter, wide bandwidth, VSWR (Voltage Standing Wave Ratio) ≤ 2, omnidirectional radiation pattern and acceptable maximum gain of >5 dB. The measurement results on the fabricated glass-based antenna show good agreement with the simulation results. The study on the alternative antenna substrates and structures is especially useful for the development of integrated patch antennas for RF energy harvesting systems. Full article
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Open AccessFeature PaperArticle Piezoelectric MEMS Resonators for Cigarette Particle Detection
Micromachines 2019, 10(2), 145; https://doi.org/10.3390/mi10020145
Received: 29 January 2019 / Revised: 17 February 2019 / Accepted: 19 February 2019 / Published: 21 February 2019
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In this work, we demonstrate the potential of a piezoelectric resonator for developing a low-cost sensor system to detect microscopic particles in real-time, which can be present in a wide variety of environments and workplaces. The sensor working principle is based on the [...] Read more.
In this work, we demonstrate the potential of a piezoelectric resonator for developing a low-cost sensor system to detect microscopic particles in real-time, which can be present in a wide variety of environments and workplaces. The sensor working principle is based on the resonance frequency shift caused by particles collected on the resonator surface. To test the sensor sensitivity obtained from mass-loading effects, an Aluminum Nitride-based piezoelectric resonator was exposed to cigarette particles in a sealed chamber. In order to determine the resonance parameters of interest, an interface circuit was implemented and included within both open-loop and closed-loop schemes for comparison. The system was capable of tracking the resonance frequency with a mass sensitivity of 8.8 Hz/ng. Although the tests shown here were proven by collecting particles from a cigarette, the results obtained in this application may have interest and can be extended towards other applications, such as monitoring of nanoparticles in a workplace environment. Full article
(This article belongs to the Special Issue 10th Anniversary of Micromachines)
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Open AccessReview A Review of Design and Fabrication of the Bionic Flapping Wing Micro Air Vehicles
Micromachines 2019, 10(2), 144; https://doi.org/10.3390/mi10020144
Received: 16 January 2019 / Revised: 7 February 2019 / Accepted: 14 February 2019 / Published: 21 February 2019
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Bionic flapping-wing micro air vehicles (FWMAVs) are promising for a variety of applications because of their flexibility and high mobility. This study reviews the state-of-the-art FWMAVs of various research institutes driven by electrical motor, mechanical transmission structure and “artificial muscle” material and then [...] Read more.
Bionic flapping-wing micro air vehicles (FWMAVs) are promising for a variety of applications because of their flexibility and high mobility. This study reviews the state-of-the-art FWMAVs of various research institutes driven by electrical motor, mechanical transmission structure and “artificial muscle” material and then elaborates on the aerodynamic mechanism of micro-winged birds and insects. Owing to their low mass budget, FWMAVs require actuators with high power density from micrometer to centimeter scales. The selection and design of the mechanical transmission should be considered in parallel with the design of the power electronic interface required to drive it. Finally, power electronic topologies suitable for driving “artificial muscle” materials used in FWMAVs are stated. Full article
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Open AccessArticle The Effect of Microfluidic Geometry on Myoblast Migration
Micromachines 2019, 10(2), 143; https://doi.org/10.3390/mi10020143
Received: 10 December 2018 / Revised: 4 February 2019 / Accepted: 19 February 2019 / Published: 21 February 2019
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In vitro systems comprised of wells interconnected by microchannels have emerged as a platform for the study of cell migration or multicellular models. In the present study, we systematically evaluated the effect of microchannel width on spontaneous myoblast migration across these microchannels—from the [...] Read more.
In vitro systems comprised of wells interconnected by microchannels have emerged as a platform for the study of cell migration or multicellular models. In the present study, we systematically evaluated the effect of microchannel width on spontaneous myoblast migration across these microchannels—from the proximal to the distal chamber. Myoblast migration was examined in microfluidic devices with varying microchannel widths of 1.5–20 µm, and in chips with uniform microchannel widths over time spans that are relevant for myoblast-to-myofiber differentiation in vitro. We found that the likelihood of spontaneous myoblast migration was microchannel width dependent and that a width of 3 µm was necessary to limit spontaneous migration below 5% of cells in the seeded well after 48 h. These results inform the future design of Polydimethylsiloxane (PDMS) microchannel-based co-culture platforms as well as future in vitro studies of myoblast migration. Full article
(This article belongs to the Special Issue Microfluidic Cell Assay Chips)
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Open AccessCorrection Correction: Shen, T. et al. High-Precision and Low-Cost Wireless 16-Channel Measurement System for Malachite Green Detection. Micromachines, 2018, 9, 646
Micromachines 2019, 10(2), 142; https://doi.org/10.3390/mi10020142
Received: 2 February 2019 / Accepted: 19 February 2019 / Published: 21 February 2019
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Abstract
In the published paper [...] Full article
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Open AccessArticle Asymmetrical Training Scheme of Binary-Memristor-Crossbar-Based Neural Networks for Energy-Efficient Edge-Computing Nanoscale Systems
Micromachines 2019, 10(2), 141; https://doi.org/10.3390/mi10020141
Received: 27 January 2019 / Revised: 15 February 2019 / Accepted: 18 February 2019 / Published: 20 February 2019
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For realizing neural networks with binary memristor crossbars, memristors should be programmed by high-resistance state (HRS) and low-resistance state (LRS), according to the training algorithms like backpropagation. Unfortunately, it takes a very long time and consumes a large amount of power in training [...] Read more.
For realizing neural networks with binary memristor crossbars, memristors should be programmed by high-resistance state (HRS) and low-resistance state (LRS), according to the training algorithms like backpropagation. Unfortunately, it takes a very long time and consumes a large amount of power in training the memristor crossbar, because the program-verify scheme of memristor-programming is based on the incremental programming pulses, where many programming and verifying pulses are repeated until the target conductance. Thus, this reduces the programming time and power is very essential for energy-efficient and fast training of memristor networks. In this paper, we compared four different programming schemes, which are F-F, C-F, F-C, and C-C, respectively. C-C means both HRS and LRS are coarse-programmed. C-F has the coarse-programmed HRS and fine LRS, respectively. F-C is vice versa of C-F. In F-F, both HRS and LRS are fine-programmed. Comparing the error-energy products among the four schemes, C-F shows the minimum error with the minimum energy consumption. The asymmetrical coarse HRS and fine LRS can reduce the time and energy during the crossbar training significantly, because only LRS is fine-programmed. Moreover, the asymmetrical C-F can maintain the network’s error as small as F-F, which is due to the coarse-programmed HRS that slightly degrades the error. Full article
(This article belongs to the Special Issue Nanoscale Switches)
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Open AccessArticle High-Performance Resistance-Switchable Multilayers of Graphene Oxide Blended with 1,3,4-Oxadiazole Acceptor Nanocomposite
Micromachines 2019, 10(2), 140; https://doi.org/10.3390/mi10020140
Received: 28 January 2019 / Revised: 14 February 2019 / Accepted: 18 February 2019 / Published: 20 February 2019
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Graphene oxide (GO) has been actively utilized in nonvolatile resistive switching random access memory (ReRAM) devices due to solution-processability, accessibility for highly scalable device fabrication for transistor-based memory, and cross-bar memory arrays. Uncontrollable oxygen functional groups of GO, however, restrict its application. To [...] Read more.
Graphene oxide (GO) has been actively utilized in nonvolatile resistive switching random access memory (ReRAM) devices due to solution-processability, accessibility for highly scalable device fabrication for transistor-based memory, and cross-bar memory arrays. Uncontrollable oxygen functional groups of GO, however, restrict its application. To obtain stable memory performance, 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) a that can serve as 1,3,4-oxadiazole acceptor was carefully introduced onto the GO framework. Better stability was achieved by increasing the weight ratio of the chemical component from 2:1 to 10:1 in all GO-based solutions. Particularly, rewritable nonvolatile memory characteristics were dependent on the ratio between PBD and GO. PBD:GO devices with a proportion of 10:1 w/w exhibited better memory performance, possessed a higher ON/OFF ratio (>102) at a lower switching voltage of −0.67 V, and had a long retention ability. The interaction between PBD and GO can be demonstrated by transmission electron microscope, scanning electron microscope, thermogravimetric analysis, fourier transform infrared spectra, Raman spectra, X-ray diffraction, and fluorescence spectra. The superior ReRAM properties of the multilayers of GO blended with the PBD nanocomposite are attributed to electron traps caused by the strong electron acceptors. Full article
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Open AccessFeature PaperArticle Graphene-Based Wireless Tube-Shaped Pressure Sensor for In Vivo Blood Pressure Monitoring
Micromachines 2019, 10(2), 139; https://doi.org/10.3390/mi10020139
Received: 11 January 2019 / Revised: 6 February 2019 / Accepted: 14 February 2019 / Published: 20 February 2019
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Abstract
We propose a wireless pressure sensor composed of a graphene sheet and a transmitter coil integrated with a polydimethylsiloxane (PDMS) tube. The pressure inside the tube was monitored wirelessly using an external receiver coil. We then monitored the typical blood pressure range, 12–20 [...] Read more.
We propose a wireless pressure sensor composed of a graphene sheet and a transmitter coil integrated with a polydimethylsiloxane (PDMS) tube. The pressure inside the tube was monitored wirelessly using an external receiver coil. We then monitored the typical blood pressure range, 12–20 kPa, using this fabricated sensor by changing the turn number of the receiver coil and the overlapping length of the coils. Furthermore, we demonstrated wireless blood pressure measurement by connecting our sensor to the blood vessel of a rat. Our results suggested that this sensor can be easily inserted between an implantable medical device and blood vessels for in vivo blood pressure monitoring. The proposed wireless pressure sensor could also be suitable for monitoring in vivo implanted medical systems, such as artificial organs and pump systems. Full article
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Open AccessArticle Nanostructured Fe,Co-Codoped MoO3 Thin Films
Micromachines 2019, 10(2), 138; https://doi.org/10.3390/mi10020138
Received: 5 February 2019 / Revised: 13 February 2019 / Accepted: 15 February 2019 / Published: 20 February 2019
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Abstract
Molybdenum oxide (MoO3) and Fe,Co-codoped MoO3 thin films obtained by spray pyrolysis have been in-depth investigated to understand the effect of Co and Fe codoping on MoO3 thin films. The effect of Fe and Co on the structural, morphological [...] Read more.
Molybdenum oxide (MoO3) and Fe,Co-codoped MoO3 thin films obtained by spray pyrolysis have been in-depth investigated to understand the effect of Co and Fe codoping on MoO3 thin films. The effect of Fe and Co on the structural, morphological and optical properties of MoO3 thin films have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray analysis (EDAX), optical and photoluminescence (PL) spectroscopy, and electropyroelectric methods. The XRD patterns demonstrated the formation of orthorhombic α-MoO3 by spray pyrolysis. SEM characterization has shown an increase in roughness of MoO3 thin films by Fe and Co doping. Optical reflectance and transmittance measurements have shown an increase in optical band gap with the increase in Fe and Co contents. Thermal conductivity and thermal diffusivity of Fe,Co-doped MoO3 were 24.10–25.86 Wm−1K−1 and 3.80 × 10−6–5.15 × 10−6 m2s−1, respectively. MoO3 thin films have shown PL emission. Doping MoO3 with Fe and Co increases emission in the visible range due to an increase number of chemisorbed oxygen atoms. The photodegradation of an aqueous solution of methylene blue (MB) depended on the content of the codoping elements (Fe,Co). The results showed that a degradation efficiency of 90% was observed after 60 min for MoO3: Fe 2%-Co 1%, while the degradation efficiency was about 35% for the undoped MoO3 thin film. Full article
(This article belongs to the Special Issue Nanostructured Photovoltaic Devices)
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Open AccessArticle Research on a Dual-Mode Infrared Liquid-Crystal Device for Simultaneous Electrically Adjusted Filtering and Zooming
Micromachines 2019, 10(2), 137; https://doi.org/10.3390/mi10020137
Received: 12 December 2018 / Revised: 25 January 2019 / Accepted: 13 February 2019 / Published: 19 February 2019
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Abstract
A new dual-mode liquid-crystal (LC) micro-device constructed by incorporating a Fabry–Perot (FP) cavity and an arrayed LC micro-lens for performing simultaneous electrically adjusted filtering and zooming in infrared wavelength range is presented in this paper. The main micro-structure is a micro-cavity consisting of [...] Read more.
A new dual-mode liquid-crystal (LC) micro-device constructed by incorporating a Fabry–Perot (FP) cavity and an arrayed LC micro-lens for performing simultaneous electrically adjusted filtering and zooming in infrared wavelength range is presented in this paper. The main micro-structure is a micro-cavity consisting of two parallel zinc selenide (ZnSe) substrates that are pre-coated with ~20-nm aluminum (Al) layers which served as their high-reflection films and electrodes. In particular, the top electrode of the device is patterned by 44 × 38 circular micro-holes of 120 μm diameter, which also means a 44 × 38 micro-lens array. The micro-cavity with a typical depth of ~12 μm is fully filled by LC materials. The experimental results show that the spectral component with needed frequency or wavelength can be selected effectively from incident micro-beams, and both the transmission spectrum and the point spread function can be adjusted simultaneously by simply varying the root-mean-square value of the signal voltage applied, so as to demonstrate a closely correlated feature of filtering and zooming. In addition, the maximum transmittance is already up to ~20% according the peak-to-valley value of the spectral transmittance curves, which exhibits nearly twice the increment compared with that of the ordinary LC-FP filtering without micro-lenses. Full article
(This article belongs to the Special Issue Optical MEMS)
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Open AccessArticle Residual Stress in Lithium Niobate Film Layer of LNOI/Si Hybrid Wafer Fabricated Using Low-Temperature Bonding Method
Micromachines 2019, 10(2), 136; https://doi.org/10.3390/mi10020136
Received: 25 October 2018 / Revised: 1 February 2019 / Accepted: 8 February 2019 / Published: 18 February 2019
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Abstract
This paper focuses on the residual stress in a lithium niobate (LN) film layer of a LN-on-insulator (LNOI)/Si hybrid wafer. This stress originates from a large mismatch between the thermal expansion coefficients of the layers. A modified surface-activated bonding method achieved fabrication of [...] Read more.
This paper focuses on the residual stress in a lithium niobate (LN) film layer of a LN-on-insulator (LNOI)/Si hybrid wafer. This stress originates from a large mismatch between the thermal expansion coefficients of the layers. A modified surface-activated bonding method achieved fabrication of a thin-film LNOI/Si hybrid wafer. This low-temperature bonding method at 100 °C showed a strong bond between the LN and SiO2 layers, which is sufficient to withstand the wafer thinning to a LN thickness of approximately 5 μm using conventional mechanical polishing. Using micro-Raman spectroscopy, the residual stress in the bonded LN film in this trilayered (LN/SiO2/Si) structure was investigated. The measured residual tensile stress in the LN film layer was approximately 155 MPa, which was similar to the value calculated by stress analysis. This study will be useful for the development of various hetero-integrated LN micro-devices, including silicon-based, LNOI-integrated photonic devices. Full article
(This article belongs to the Special Issue Heterogeneous Integration for Optical Micro and Nanosystems)
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Open AccessArticle An Experimental Study of 3D Electrode-Facilitated Particle Traffic Flow-Focusing Driven by Induced-Charge Electroosmosis
Micromachines 2019, 10(2), 135; https://doi.org/10.3390/mi10020135
Received: 30 January 2019 / Revised: 12 February 2019 / Accepted: 15 February 2019 / Published: 18 February 2019
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Abstract
In this paper we present a novel microfluidic approach for continuous, rapid and switchable particle concentration, using induced-charge electroosmosis (ICEO) in 3D electrode layouts. Field-effect control on non-linear electroosmosis in the transverse direction greatly facilitates a selective concentration of biological yeast cells from [...] Read more.
In this paper we present a novel microfluidic approach for continuous, rapid and switchable particle concentration, using induced-charge electroosmosis (ICEO) in 3D electrode layouts. Field-effect control on non-linear electroosmosis in the transverse direction greatly facilitates a selective concentration of biological yeast cells from a straight main microchannel into one of the three downstream branch channels in our microfluidic device. For the geometry configuration of 3D driving electrode plates on sidewalls and a 2D planar gate electrode strip on the channel bottom surface, we briefly describe the underlying physics of an ICEO-based particle flow-focusing method, and provide relevant simulation results to show how gate voltage amplitude can be used to guide the motion trajectory of the concentrated particle stream. With a relatively simple geometrical configuration, the proposed microfluidic device provides new possibilities to controllably concentrate micro/nanoparticles in continuous flow by using ICEO, and is suitable for a high-throughput front-end cell concentrator interfacing with various downstream biosensors. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume III)
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Open AccessArticle High-G Calibration Denoising Method for High-G MEMS Accelerometer Based on EMD and Wavelet Threshold
Micromachines 2019, 10(2), 134; https://doi.org/10.3390/mi10020134
Received: 27 December 2018 / Revised: 13 February 2019 / Accepted: 15 February 2019 / Published: 18 February 2019
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Abstract
High-G MEMS accelerometers have been widely used in monitoring natural disasters and other fields. In order to improve the performance of High-G MEMS accelerometers, a denoising method based on the combination of empirical mode decomposition (EMD) and wavelet threshold is proposed. Firstly, EMD [...] Read more.
High-G MEMS accelerometers have been widely used in monitoring natural disasters and other fields. In order to improve the performance of High-G MEMS accelerometers, a denoising method based on the combination of empirical mode decomposition (EMD) and wavelet threshold is proposed. Firstly, EMD decomposition is performed on the output of the main accelerometer to obtain the intrinsic mode function (IMF). Then, the continuous mean square error rule is used to find energy cut-off point, and then the corresponding high frequency IMF component is denoised by wavelet threshold. Finally, the processed high-frequency IMF component is superposed with the low-frequency IMF component, and the reconstructed signal is denoised signal. Experimental results show that this method integrates the advantages of EMD and wavelet threshold and can retain useful signals to the maximum extent. The impact peak and vibration characteristics are 0.003% and 0.135% of the original signal, respectively, and it reduces the noise of the original signal by 96%. Full article
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Open AccessArticle On-Chip Cell Incubator for Simultaneous Observation of Culture with and without Periodic Hydrostatic Pressure
Micromachines 2019, 10(2), 133; https://doi.org/10.3390/mi10020133
Received: 12 January 2019 / Revised: 15 February 2019 / Accepted: 15 February 2019 / Published: 17 February 2019
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Abstract
This paper proposes a microfluidic device which can perform simultaneous observation on cell growth with and without applying periodic hydrostatic pressure (Yokoyama et al. Sci. Rep. 2017, 7, 427). The device is called on-chip cell incubator. It is known that culture [...] Read more.
This paper proposes a microfluidic device which can perform simultaneous observation on cell growth with and without applying periodic hydrostatic pressure (Yokoyama et al. Sci. Rep. 2017, 7, 427). The device is called on-chip cell incubator. It is known that culture with periodic hydrostatic pressure benefits the elasticity of a cultured cell sheet based on the results in previous studies, but how the cells respond to such a stimulus during the culture is not yet clear. In this work, we focused on cell behavior under periodic hydrostatic pressure from the moment of cell seeding. The key advantage of the proposed device is that we can compare the results with and without periodic hydrostatic pressure while all other conditions were kept the same. According to the results, we found that cell sizes under periodic hydrostatic pressure increase faster than those under atmospheric pressure, and furthermore, a frequency-dependent fluctuation of cell size was found using Fourier analysis. Full article
(This article belongs to the Special Issue Microfluidics for Cell and Other Organisms)
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Open AccessArticle A Silicon-based Coral-like Nanostructured Microfluidics to Isolate Rare Cells in Human Circulation: Validation by SK-BR-3 Cancer Cell Line and Its Utility in Circulating Fetal Nucleated Red Blood Cells
Micromachines 2019, 10(2), 132; https://doi.org/10.3390/mi10020132
Received: 24 January 2019 / Revised: 13 February 2019 / Accepted: 14 February 2019 / Published: 17 February 2019
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Abstract
Circulating fetal cells (CFCs) in maternal blood are rare but have a strong potential to be the target for noninvasive prenatal diagnosis (NIPD). “Cell RevealTM system” is a silicon-based microfluidic platform capable to capture rare cell populations in human circulation. The platform [...] Read more.
Circulating fetal cells (CFCs) in maternal blood are rare but have a strong potential to be the target for noninvasive prenatal diagnosis (NIPD). “Cell RevealTM system” is a silicon-based microfluidic platform capable to capture rare cell populations in human circulation. The platform is recently optimized to enhance the capture efficiency and system automation. In this study, spiking tests of SK-BR-3 breast cancer cells were used for the evaluation of capture efficiency. Then, peripheral bloods from 14 pregnant women whose fetuses have evidenced non-maternal genomic markers (e.g., de novo pathogenic copy number changes) were tested for the capture of circulating fetal nucleated red blood cells (fnRBCs). Captured cells were subjected to fluorescent in situ hybridization (FISH) on chip or recovered by an automated cell picker for molecular genetic analyses. The capture rate for the spiking tests is estimated as 88.1%. For the prenatal study, 2–71 fnRBCs were successfully captured from 2 mL of maternal blood in all pregnant women. The captured fnRBCs were verified to be from fetal origin. Our results demonstrated that the Cell RevealTM system has a high capture efficiency and can be used for fnRBC capture that is feasible for the genetic diagnosis of fetuses without invasive procedures. Full article
(This article belongs to the Special Issue Microfluidics for Cell and Other Organisms)
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Open AccessArticle A Microfluidic Micropipette Aspiration Device to Study Single-Cell Mechanics Inspired by the Principle of Wheatstone Bridge
Micromachines 2019, 10(2), 131; https://doi.org/10.3390/mi10020131
Received: 10 January 2019 / Revised: 11 February 2019 / Accepted: 11 February 2019 / Published: 16 February 2019
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Abstract
The biomechanical properties of single cells show great potential for early disease diagnosis and effective treatments. In this study, a microfluidic device was developed for quantifying the mechanical properties of a single cell. Micropipette aspiration was integrated into a microfluidic device that mimics [...] Read more.
The biomechanical properties of single cells show great potential for early disease diagnosis and effective treatments. In this study, a microfluidic device was developed for quantifying the mechanical properties of a single cell. Micropipette aspiration was integrated into a microfluidic device that mimics a classical Wheatstone bridge circuit. This technique allows us not only to effectively alter the flow direction for single-cell trapping, but also to precisely control the pressure exerted on the aspirated cells, analogous to the feature of the Wheatstone bridge that can precisely control bridge voltage and current. By combining the micropipette aspiration technique into the microfluidic device, we can effectively trap the microparticles and Hela cells as well as measure the deformability of cells. The Young’s modulus of Hela cells was evaluated to be 387 ± 77 Pa, which is consistent with previous micropipette aspiration studies. The simplicity, precision, and usability of our device show good potential for biomechanical trials in clinical diagnosis and cell biology research. Full article
(This article belongs to the Special Issue Microfluidics for Cell and Other Organisms)
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Open AccessArticle Phototactic Algae-Driven Unidirectional Transport of Submillimeter-Sized Cargo in a Microchannel
Micromachines 2019, 10(2), 130; https://doi.org/10.3390/mi10020130
Received: 18 January 2019 / Revised: 7 February 2019 / Accepted: 8 February 2019 / Published: 16 February 2019
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Abstract
The sensing and actuation capabilities of biological cells integrated with artificial components have been used to create autonomous microsystems. For creating autonomous microsystems, the unidirectional transport of a submillimeter-sized cargo with stimuli responsive bio-motors should be developed as a fundamental motion. This study [...] Read more.
The sensing and actuation capabilities of biological cells integrated with artificial components have been used to create autonomous microsystems. For creating autonomous microsystems, the unidirectional transport of a submillimeter-sized cargo with stimuli responsive bio-motors should be developed as a fundamental motion. This study aims to use Volvox as a light-controlled microrobot to achieve the unidirectional transport of a submillimeter-sized cargo. We show the fabrication of a guide structure, cargo, and light irradiation platform for a unidirectional actuation. The fundamental performances of each component were investigated, and the motions of Volvox were controlled in a microchamber with the developed light irradiation platform. All components were integrated to demonstrate the unidirectional actuation of a block by Volvox. We discuss the dynamics of the mechanical motions. Full article
(This article belongs to the Special Issue Micro/Nanomotors 2018)
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Open AccessArticle Detection of Hepatitis C Virus Core Protein in Serum Using Aptamer-Functionalized AFM Chips
Micromachines 2019, 10(2), 129; https://doi.org/10.3390/mi10020129
Received: 28 December 2018 / Revised: 8 February 2019 / Accepted: 11 February 2019 / Published: 15 February 2019
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Abstract
In the present study, we demonstrate atomic force microscopy (AFM)-based detection of hepatitis C virus (HCV) particles in serum samples using a chip with aptamer-functionalized surface (apta-based AFM chip). The target particles, containing core antigen of HCV (HCVcoreAg protein), were biospecifically captured onto [...] Read more.
In the present study, we demonstrate atomic force microscopy (AFM)-based detection of hepatitis C virus (HCV) particles in serum samples using a chip with aptamer-functionalized surface (apta-based AFM chip). The target particles, containing core antigen of HCV (HCVcoreAg protein), were biospecifically captured onto the chip surface from 1 mL of test solution containing 10 µL of serum collected from a hepatitis C patient. The registration of aptamer/antigen complexes on the chip surface was performed by AFM. The aptamers used in the present study were initially developed for therapeutic purposes; herein, these aptamers have been successfully utilized as probe molecules for HCVcoreAg detection in the presence of a complex protein matrix (human serum). The results obtained herein can be used for the development of detection systems that employ affine enrichment for protein detection. Full article
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