Micromachines

11 pages, 8315 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Improved High-Yield PMMA/Graphene Pressure Sensor and Sealed Gas Effect Analysis

by Ying Liu, Yong Zhang, Xin Lin, Ke-hong Lv, Peng Yang, Jing Qiu and Guan-jun Liu

Micromachines 2020, 11(9), 786; https://doi.org/10.3390/mi11090786 - 19 Aug 2020

Cited by 7 | Viewed by 2926

Graphene with atomic thickness possesses excellent mechanical and electrical properties, which hold great potential for high performance pressure sensing. The exposed electron of graphene is always cross-sensitive to any pollution absorbed or desorbed on the surface, from which the long-term stability of the [...] Read more.

Graphene with atomic thickness possesses excellent mechanical and electrical properties, which hold great potential for high performance pressure sensing. The exposed electron of graphene is always cross-sensitive to any pollution absorbed or desorbed on the surface, from which the long-term stability of the graphene pressure sensor suffers a lot. This is one of the main obstacles towards graphene commercial applications. In this paper, we utilized polymethylmethacrylate (PMMA)/graphene heterostructure to isolate graphene from the ambient environment and enhance its strength simultaneously. PMMA/graphene pressure sensors, with the finite-depth cavities and the through-hole cavities separately, were made for comparative study. The through-hole device obtained a comparable sensitivity per unit area to the state of the art of the bare graphene pressure sensor, since there were no leaking cracks or defects. Both the sensitivity and stability of the through-hole sensor are better than those of the sensor with 285-nm-deep cavities, which is due to the sealed gas effect in the pressure cavity. A modified piezoresistive model was derived by considering the pressure change of the sealed gas in the pressure cavity. The calculated result of the new model is consistent with the experimental results. Our findings point out a promising route for performance optimization of graphene pressure sensors. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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16 pages, 8383 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Random Access Addressing of MEMS Electrostatic Shutter Array for Multi-Object Astronomical Spectroscopy

by Xufeng Liu, Takuya Takahashi, Masahiro Konishi, Kentaro Motohara and Hiroshi Toshiyoshi

Micromachines 2020, 11(8), 782; https://doi.org/10.3390/mi11080782 - 17 Aug 2020

Cited by 4 | Viewed by 3605

Abstract

An extended version of cross-bar type addressing technique is developed for three-port electrostatic micro shutters arranged in an arrayed format. A microelectromechanical systems (MEMS) shutter blade suspended by a pair of torsion beams works as a movable electrode that is either attracted upwards [...] Read more.

An extended version of cross-bar type addressing technique is developed for three-port electrostatic micro shutters arranged in an arrayed format. A microelectromechanical systems (MEMS) shutter blade suspended by a pair of torsion beams works as a movable electrode that is either attracted upwards to the cover plate to close the aperture or retracted downwards into the through-hole to open it. Tri-state positioning of the shutter—i.e., open, rest, and close—is controlled by the hysteresis loop of the electrostatic pull-in and release behavior using the combination of the voltages applied to the shutter, the cover, and the substrate. Random access addressing of the shutters is demonstrated by a control system composed of MATLAB-coded Arduino electronics. The shutter array developed in this work is for a sub-cluster of a reconfigurable shutter array under development for a multi-object galactic astronomy. Full article

(This article belongs to the Special Issue Optical MEMS, Volume II)

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17 pages, 4661 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Development of Fully Flexible Tactile Pressure Sensor with Bilayer Interlaced Bumps for Robotic Grasping Applications

by Lingfeng Zhu, Yancheng Wang, Deqing Mei and Chengpeng Jiang

Micromachines 2020, 11(8), 770; https://doi.org/10.3390/mi11080770 - 12 Aug 2020

Cited by 20 | Viewed by 5344

Abstract

Flexible tactile sensors have been utilized in intelligent robotics for human-machine interaction and healthcare monitoring. The relatively low flexibility, unbalanced sensitivity and sensing range of the tactile sensors are hindering the accurate tactile information perception during robotic hand grasping of different objects. This [...] Read more.

Flexible tactile sensors have been utilized in intelligent robotics for human-machine interaction and healthcare monitoring. The relatively low flexibility, unbalanced sensitivity and sensing range of the tactile sensors are hindering the accurate tactile information perception during robotic hand grasping of different objects. This paper developed a fully flexible tactile pressure sensor, using the flexible graphene and silver composites as the sensing element and stretchable electrodes, respectively. As for the structural design of the tactile sensor, the proposed bilayer interlaced bumps can be used to convert external pressure into the stretching of graphene composites. The fabricated tactile sensor exhibits a high sensing performance, including relatively high sensitivity (up to 3.40% kPa⁻¹), wide sensing range (200 kPa), good dynamic response, and considerable repeatability. Then, the tactile sensor has been integrated with the robotic hand finger, and the grasping results have indicated the capability of using the tactile sensor to detect the distributed pressure during grasping applications. The grasping motions, properties of the objects can be further analyzed through the acquired tactile information in time and spatial domains, demonstrating the potential applications of the tactile sensor in intelligent robotics and human-machine interfaces. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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12 pages, 1376 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Parallel-Channel Electrotaxis and Neuron Screening of Caenorhabditis elegans

by Khaled Youssef, Daphne Archonta, Terrance Kubiseski, Anurag Tandon and Pouya Rezai

Micromachines 2020, 11(8), 756; https://doi.org/10.3390/mi11080756 - 4 Aug 2020

Cited by 8 | Viewed by 3447

Abstract

In this paper, we report a novel microfluidic method to conduct a Caenorhabditis elegans electrotaxis movement assay and neuronal imaging on up to 16 worms in parallel. C. elegans is a model organism for neurodegenerative disease and movement disorders such as Parkinson’s disease [...] Read more.

In this paper, we report a novel microfluidic method to conduct a Caenorhabditis elegans electrotaxis movement assay and neuronal imaging on up to 16 worms in parallel. C. elegans is a model organism for neurodegenerative disease and movement disorders such as Parkinson’s disease (PD), and for screening chemicals that alleviate protein aggregation, neuronal death, and movement impairment in PD. Electrotaxis of C. elegans in microfluidic channels has led to the development of neurobehavioral screening platforms, but enhancing the throughput of the electrotactic behavioral assay has remained a challenge. Our device consisted of a hierarchy of tree-like channels for worm loading into 16 parallel electrotaxis screening channels with equivalent electric fields. Tapered channels at the ends of electrotaxis channels were used for worm immobilization and fluorescent imaging of neurons. Parallel electrotaxis of worms was first validated against established single-worm electrotaxis phenotypes. Then, mutant screening was demonstrated using the NL5901 strain, carrying human

α

-synuclein in the muscle cells, by showing the associated electrotaxis defects in the average speed, body bend frequency (BBF), and electrotaxis time index (ETI). Moreover, chemical screening of a PD worm model was shown by exposing the BZ555 strain, expressing green fluorescence protein (GFP) in the dopaminergic neurons (DNs), to 6-hydroxydopamine neurotoxin. The neurotoxin-treated worms exhibited a reduction in electrotaxis swimming speed, BBF, ETI, and DNs fluorescence intensity. We envision our technique to be used widely in C. elegans-based movement disorder assays to accelerate behavioral and cellular phenotypic investigations. Full article

(This article belongs to the Special Issue Organisms-on-Chips)

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14 pages, 5613 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Facile Fabrication of Thin-Bottom Round-Well Plates Using the Deformation of PDMS Molds and Their Application for Single-Cell PCR

by Shinya Yamahira and Yuji Heike

Micromachines 2020, 11(8), 748; https://doi.org/10.3390/mi11080748 - 31 Jul 2020

Cited by 2 | Viewed by 5660

Abstract

Recently, microdevices made of resins have been strongly supporting cell analysis in a range of fields, from fundamental life science research to medical applications. Many microdevices are fabricated by molding resin to a mold made precisely from rigid materials. However, because dimensional errors [...] Read more.

Recently, microdevices made of resins have been strongly supporting cell analysis in a range of fields, from fundamental life science research to medical applications. Many microdevices are fabricated by molding resin to a mold made precisely from rigid materials. However, because dimensional errors in the mold are also accurately printed to the products, the accuracy of the product is limited to less than the accuracy of the rigid mold. Therefore, we hypothesized that if dimensional errors could be self-corrected by elastic molds, microdevices could be facilely fabricated with precision beyond that of molds. In this paper, we report a novel processing strategy in which an elastic mold made of polymethylsiloxane (PDMS) deforms to compensate for the dimensional error on the products. By heat-press molding a polycarbonate plate using a mold that has 384 PDMS convexes with a large dimensional error of height of ± 15.6 µm in standard deviation, a 384-round-well plate with a bottom thickness 13.3 ± 2.3 µm (n = 384) was easily fabricated. Finally, single-cell observation and polymerase chain reactions (PCRs) demonstrated the application of the products made by elastic PDMS molds. Therefore, this processing method is a promising strategy for facile, low-cost, and higher precision microfabrication. Full article

(This article belongs to the Special Issue Micro and Nano Devices for Cell Analysis)

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12 pages, 2972 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Curved Structure of Si by Improving Etching Direction Controllability in Magnetically Guided Metal-Assisted Chemical Etching

by Tae Kyoung Kim, Jee-Hwan Bae, Juyoung Kim, Min Kyung Cho, Yu-Chan Kim, Sungho Jin and Dongwon Chun

Micromachines 2020, 11(8), 744; https://doi.org/10.3390/mi11080744 - 30 Jul 2020

Cited by 7 | Viewed by 3885

Abstract

Metal-assisted chemical etching (MACE) is widely used to fabricate micro-/nano-structured Si owing to its simplicity and cost-effectiveness. The technique of magnetically guided MACE, involving MACE with a tri-layer metal catalyst, was developed to improve etching speed as well as to adjust the etching [...] Read more.

Metal-assisted chemical etching (MACE) is widely used to fabricate micro-/nano-structured Si owing to its simplicity and cost-effectiveness. The technique of magnetically guided MACE, involving MACE with a tri-layer metal catalyst, was developed to improve etching speed as well as to adjust the etching direction using an external magnetic field. However, the controllability of the etching direction diminishes with an increase in the etching dimension, owing to the corrosion of Fe due to the etching solution; this impedes the wider application of this approach for the fabrication of complex micro Si structures. In this study, we modified a tri-layer metal catalyst (Au/Fe/Au), wherein the Fe layer was encapsulated to improve direction controllability; this improved controllability was achieved by protecting Fe against the corrosion caused by the etching solution. We demonstrated curved Si microgroove arrays via magnetically guided MACE with Fe encapsulated in the tri-layer catalyst. Furthermore, the curvature in the curved Si microarrays could be modulated via an external magnetic field, indicating that direction controllability could be maintained even for the magnetically guided MACE of bulk Si. The proposed fabrication method developed for producing curved Si microgroove arrays can be applied to electronic devices and micro-electromechanical systems. Full article

(This article belongs to the Special Issue Micro- and Nano-Fabrication by Metal Assisted Chemical Etching)

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12 pages, 5457 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Single-Grain Gate-All-Around Si Nanowire FET Using Low-Thermal-Budget Processes for Monolithic Three-Dimensional Integrated Circuits

by Tung-Ying Hsieh, Ping-Yi Hsieh, Chih-Chao Yang, Chang-Hong Shen, Jia-Min Shieh, Wen-Kuan Yeh and Meng-Chyi Wu

Micromachines 2020, 11(8), 741; https://doi.org/10.3390/mi11080741 - 30 Jul 2020

Cited by 4 | Viewed by 4490

Abstract

We introduce a single-grain gate-all-around (GAA) Si nanowire (NW) FET using the location-controlled-grain technique and several innovative low-thermal budget processes, including green nanosecond laser crystallization, far-infrared laser annealing, and hybrid laser-assisted salicidation, that keep the substrate temperature (T_sub) lower than 400 [...] Read more.

We introduce a single-grain gate-all-around (GAA) Si nanowire (NW) FET using the location-controlled-grain technique and several innovative low-thermal budget processes, including green nanosecond laser crystallization, far-infrared laser annealing, and hybrid laser-assisted salicidation, that keep the substrate temperature (T_sub) lower than 400 °C for monolithic three-dimensional integrated circuits (3D-ICs). The detailed process verification of a low-defect GAA nanowire and electrical characteristics were investigated in this article. The GAA Si NW FETs, which were intentionally fabricated within the controlled Si grain, exhibit a steeper subthreshold swing (S.S.) of about 65 mV/dec., higher driving currents of 327 µA/µm (n-type) and 297 µA/µm (p-type) @ V_th ± 0.8 V, and higher I_on/I_off (>10⁵ @|V_d| = 1 V) and have a narrower electrical property distribution. In addition, the proposed Si NW FETs with a GAA structure were found to be less sensitive to V_th roll-off and S.S. degradation compared to the omega(Ω)-gate Si FETs. It enables ultrahigh-density sequentially stackable integrated circuits with superior performance and low power consumption for future mobile and neuromorphic applications. Full article

(This article belongs to the Special Issue Monolithic 3D Chips)

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13 pages, 1633 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

RhoA and Rac1 in Liver Cancer Cells: Induction of Overexpression Using Mechanical Stimulation

by Sharda Yadav, Navid Kashaninejad and Nam-Trung Nguyen

Micromachines 2020, 11(8), 729; https://doi.org/10.3390/mi11080729 - 28 Jul 2020

Cited by 15 | Viewed by 3018

Abstract

Liver cancer, especially hepatocellular carcinoma (HCC), is an aggressive disease with an extremely high mortality rate. Unfortunately, no promising markers are currently available for the early diagnosis of this disease. Thus, a reliable biomarker reflecting the early behaviour of the tumour will be [...] Read more.

Liver cancer, especially hepatocellular carcinoma (HCC), is an aggressive disease with an extremely high mortality rate. Unfortunately, no promising markers are currently available for the early diagnosis of this disease. Thus, a reliable biomarker reflecting the early behaviour of the tumour will be valuable for diagnosis and treatment. The Ras homologous (Rho) GTPases, which belong to the small guanosine triphosphate (GTP) binding proteins, have been reported to play an important role in mediating liver cancer based on their important function in cytoskeletal reorganisation. These proteins can be either oncogenic or tumour suppressors. They are also associated with the acquirement of malignant features by cancer cells. The overexpression of RhoA and Rac1, members of the Rho GTPases, have been linked with carcinogenesis and the progression of different types of cancer. In the quest of elucidating the role of mechanical stimulation in the mechanobiology of liver cancer cells, this paper evaluates the effect of stretching on the expression levels of RhoA and Rac1 in different types of liver cancers. It is shown that that stretching liver cancer cells significantly increases the expression levels of RhoA and Rac1 in HCC and cholangiocarcinoma cell lines. We hypothesise that this relatively simple and sensitive method could be helpful for screening biological features and provide suitable treatment guidance for liver cancer patients. Full article

(This article belongs to the Special Issue Mechanobiology and Biologically Inspired Engineering)

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20 pages, 4522 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances in Vertically Aligned Nanowires for Photonics Applications

by Sehui Chang, Gil Ju Lee and Young Min Song

Micromachines 2020, 11(8), 726; https://doi.org/10.3390/mi11080726 - 26 Jul 2020

Cited by 13 | Viewed by 5329

Abstract

Over the past few decades, nanowires have arisen as a centerpiece in various fields of application from electronics to photonics, and, recently, even in bio-devices. Vertically aligned nanowires are a particularly decent example of commercially manufacturable nanostructures with regard to its packing fraction [...] Read more.

Over the past few decades, nanowires have arisen as a centerpiece in various fields of application from electronics to photonics, and, recently, even in bio-devices. Vertically aligned nanowires are a particularly decent example of commercially manufacturable nanostructures with regard to its packing fraction and matured fabrication techniques, which is promising for mass-production and low fabrication cost. Here, we track recent advances in vertically aligned nanowires focused in the area of photonics applications. Begin with the core optical properties in nanowires, this review mainly highlights the photonics applications such as light-emitting diodes, lasers, spectral filters, structural coloration and artificial retina using vertically aligned nanowires with the essential fabrication methods based on top-down and bottom-up approaches. Finally, the remaining challenges will be briefly discussed to provide future directions. Full article

(This article belongs to the Special Issue Nanowires and Nanoprobes – Functionalized Arrays)

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14 pages, 14832 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Robot Selection Problem for Mini-Parallel Kinematic Machines: A Task-Driven Approach to the Selection Attributes Identification

by Cinzia Amici, Nicola Pellegrini and Monica Tiboni

Micromachines 2020, 11(8), 711; https://doi.org/10.3390/mi11080711 - 22 Jul 2020

Cited by 13 | Viewed by 2805

Abstract

In the last decades, the Robot Selection Problem (RSP) has been widely investigated, and the importance of properly structuring the decision problem has been stated. Crucial aspect in this process is the correct identification of the robot attributes, which should be limited in [...] Read more.

In the last decades, the Robot Selection Problem (RSP) has been widely investigated, and the importance of properly structuring the decision problem has been stated. Crucial aspect in this process is the correct identification of the robot attributes, which should be limited in number as much as possible, but should be also able to detect at best the peculiar requirements of specific applications. Literature describes several attributes examples, but mainly dedicated to traditional industrial tasks, and applied to the selection of conventional industrial robots. After a synthetic review of the robot attributes depicted in the RSP literature, presented with a custom taxonomy, this paper proposes a set of possible requirements for the selection problem of small scale parallel kinematic machines (PKMs). The RSP is based on a task-driven approach: two mini-manipulators are compared as equivalent linear actuators to be integrated within a more complex system, for the application in both an industrial and a biomedical environment. The set of identified criteria for the two environments is proposed in the results and investigated with respect to working conditions and context in the discussion, emphasizing limits and strength points of this approach; finally, the conclusions synthesizes the main results. Full article

(This article belongs to the Special Issue Sustainable and Reconfigurable Machines for Mini and Micro-Applications)

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12 pages, 2629 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Safe Coated Microneedles with Reduced Puncture Occurrence after Administration

by Hye-Rin Jeong, Hyesun Jun, Hye-Ran Cha, Jae Myun Lee and Jung-Hwan Park

Micromachines 2020, 11(8), 710; https://doi.org/10.3390/mi11080710 - 22 Jul 2020

Cited by 17 | Viewed by 3732

Abstract

The goal of this study is the preparation of safer coated microneedles so that tips remaining after the initial use are less likely to be reinserted on a second use. Twelve groups of uncoated microneedles (u-MNs) were prepared from the combination of three [...] Read more.

The goal of this study is the preparation of safer coated microneedles so that tips remaining after the initial use are less likely to be reinserted on a second use. Twelve groups of uncoated microneedles (u-MNs) were prepared from the combination of three different aspect ratios (height to base width) and four kinds of polymer (polyethylene (PE), polypropylene (PP), nylon and polylactic acid (PLA)). After coating the u-MNs with polyvinyl alcohol formulation to make coated MNs (c-MNs), the force displacement of the u-MNs and the c-MNs was measured. The aspect ratio was reduced from 2.2, 2.5 and 3.0 with u-MNs to 1.3, 1.4 and 1.6 with c-MNs, respectively, after the coating formulation was applied to the MNs. All PLA MNs had a puncture performance of more than 95%. However, the puncture performance of u-MNs made of PE and of PP with a 3.0 aspect ratio was only 8% and 53%, respectively, whereas the rates of c-MNs made of PE and of PP were 82% and 95%, respectively. In animal experiments with PP MNs with a 3.0 aspect ratio, the 59% rate of puncture performance with u-MNs increased to above 96% with c-MNs and fell to 13% for r-MNs. Safe c-MNs can overcome the disadvantages of standard c-MNs by reducing the probable contamination of remaining tips after use. Safe c-MNs have advantages over standard c-MNs in terms of humidity resistance, reasonable cost, sterilization process and short processing time through the separate process of u-MN preparation and simple dip-coating. Full article

(This article belongs to the Special Issue Microneedles)

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17 pages, 5201 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Design and Characterization of an EEG-Hat for Reliable EEG Measurements

by Takumi Kawana, Yuri Yoshida, Yuta Kudo, Chiho Iwatani and Norihisa Miki

Micromachines 2020, 11(7), 635; https://doi.org/10.3390/mi11070635 - 28 Jun 2020

Cited by 11 | Viewed by 4150

Abstract

In this study, a new hat-type electroencephalogram (EEG) device with candle-like microneedle electrodes (CMEs), called an EEG-Hat, was designed and fabricated. CMEs are dry EEG electrodes that can measure high-quality EEG signals without skin treatment or conductive gels. One of the challenges in [...] Read more.

In this study, a new hat-type electroencephalogram (EEG) device with candle-like microneedle electrodes (CMEs), called an EEG-Hat, was designed and fabricated. CMEs are dry EEG electrodes that can measure high-quality EEG signals without skin treatment or conductive gels. One of the challenges in the measurement of high-quality EEG signals is the fixation of electrodes to the skin, i.e., the design of a good EEG headset. The CMEs were able to achieve good contact with the scalp for heads of different sizes and shapes, and the EEG-Hat has a shutter mechanism to separate the hair and ensure good contact between the CMEs and the scalp. Simultaneous measurement of EEG signals from five measurement points on the scalp was successfully conducted after a simple and brief setup process. The EEG-Hat is expected to contribute to the advancement of EEG research. Full article

(This article belongs to the Special Issue Selected Papers from the 10th Symposium on Micro-Nano Science and Technology on Micromachines)

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14 pages, 4999 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Closable Valves and Channels for Polymeric Microfluidic Devices

by Charles P. Clark, M. Shane Woolf, Sarah L. Karstens, Hannah M. Lewis, Aeren Q. Nauman and James P. Landers

Micromachines 2020, 11(7), 627; https://doi.org/10.3390/mi11070627 - 27 Jun 2020

Cited by 7 | Viewed by 3780

Abstract

This study explores three unique approaches for closing valves and channels within microfluidic systems, specifically multilayer, centrifugally driven polymeric devices. Precise control over the cessation of liquid movement is achieved through either the introduction of expanding polyurethane foam, the application of direct contact [...] Read more.

This study explores three unique approaches for closing valves and channels within microfluidic systems, specifically multilayer, centrifugally driven polymeric devices. Precise control over the cessation of liquid movement is achieved through either the introduction of expanding polyurethane foam, the application of direct contact heating, or the redeposition of xerographic toner via chloroform solvation and evaporation. Each of these techniques modifies the substrate of the microdevice in a different way. All three are effective at closing a previously open fluidic pathway after a desired unit operation has taken place, i.e., sample metering, chemical reaction, or analytical measurement. Closing previously open valves and channels imparts stringent fluidic control—preventing backflow, maintaining pressurized chambers within the microdevice, and facilitating sample fractionation without cross-contamination. As such, a variety of microfluidic bioanalytical systems would benefit from the integration of these valving approaches. Full article

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17 pages, 6565 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A mm-Sized Free-Floating Wireless Implantable Opto-Electro Stimulation Device

by Yaoyao Jia, Yan Gong, Arthur Weber, Wen Li and Maysam Ghovanloo

Micromachines 2020, 11(6), 621; https://doi.org/10.3390/mi11060621 - 25 Jun 2020

Cited by 4 | Viewed by 5470

Abstract

Towards a distributed neural interface, consisting of multiple miniaturized implants, for interfacing with large-scale neuronal ensembles over large brain areas, this paper presents a mm-sized free-floating wirelessly-powered implantable opto-electro stimulation (FF-WIOS2) device equipped with 16-ch optical and 4-ch electrical stimulation for reconfigurable neuromodulation. [...] Read more.

Towards a distributed neural interface, consisting of multiple miniaturized implants, for interfacing with large-scale neuronal ensembles over large brain areas, this paper presents a mm-sized free-floating wirelessly-powered implantable opto-electro stimulation (FF-WIOS2) device equipped with 16-ch optical and 4-ch electrical stimulation for reconfigurable neuromodulation. The FF-WIOS2 is wirelessly powered and controlled through a 3-coil inductive link at 60 MHz. The FF-WIOS2 receives stimulation parameters via on-off keying (OOK) while sending its rectified voltage information to an external headstage for closed-loop power control (CLPC) via load-shift-keying (LSK). The FF-WIOS2 system-on-chip (SoC), fabricated in a 0.35-µm standard CMOS process, employs switched-capacitor-based stimulation (SCS) architecture to provide large instantaneous current needed for surpassing the optical stimulation threshold. The SCS charger charges an off-chip capacitor up to 5 V at 37% efficiency. At the onset of stimulation, the capacitor delivers charge with peak current in 1.7–12 mA range to a micro-LED (µLED) array for optical stimulation or 100–700 μA range to a micro-electrode array (MEA) for biphasic electrical stimulation. Active and passive charge balancing circuits are activated in electrical stimulation mode to ensure stimulation safety. In vivo experiments conducted on three anesthetized rats verified the efficacy of the two stimulation mechanisms. The proposed FF-WIOS2 is potentially a reconfigurable tool for performing untethered neuromodulation. Full article

(This article belongs to the Special Issue Implantable Microdevices, Volume II)

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33 pages, 2680 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Tissue-Engineered Models for Glaucoma Research

by Renhao Lu, Paul A. Soden and Esak Lee

Micromachines 2020, 11(6), 612; https://doi.org/10.3390/mi11060612 - 24 Jun 2020

Cited by 7 | Viewed by 5592

Abstract

Glaucoma is a group of optic neuropathies characterized by the progressive degeneration of retinal ganglion cells (RGCs). Patients with glaucoma generally experience elevations in intraocular pressure (IOP), followed by RGC death, peripheral vision loss and eventually blindness. However, despite the substantial economic and [...] Read more.

Glaucoma is a group of optic neuropathies characterized by the progressive degeneration of retinal ganglion cells (RGCs). Patients with glaucoma generally experience elevations in intraocular pressure (IOP), followed by RGC death, peripheral vision loss and eventually blindness. However, despite the substantial economic and health-related impact of glaucoma-related morbidity worldwide, the surgical and pharmacological management of glaucoma is still limited to maintaining IOP within a normal range. This is in large part because the underlying molecular and biophysical mechanisms by which glaucomatous changes occur are still unclear. In the present review article, we describe current tissue-engineered models of the intraocular space that aim to advance the state of glaucoma research. Specifically, we critically evaluate and compare both 2D and 3D-culture models of the trabecular meshwork and nerve fiber layer, both of which are key players in glaucoma pathophysiology. Finally, we point out the need for novel organ-on-a-chip models of glaucoma that functionally integrate currently available 3D models of the retina and the trabecular outflow pathway. Full article

(This article belongs to the Special Issue Mechanobiology and Biologically Inspired Engineering)

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17 pages, 5749 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

3D Printed Monolithic Microreactors for Real-Time Detection of Klebsiella pneumoniae and the Resistance Gene bla_NDM-1 by Recombinase Polymerase Amplification

by Ole Behrmann, Matthias Hügle, Franz Eckardt, Iris Bachmann, Cecilia Heller, Marina Schramm, Carrie Turner, Frank T. Hufert and Gregory Dame

Micromachines 2020, 11(6), 595; https://doi.org/10.3390/mi11060595 - 17 Jun 2020

Cited by 6 | Viewed by 3679

Abstract

We investigate the compatibility of three 3D printing materials towards real-time recombinase polymerase amplification (rtRPA). Both the general ability of the rtRPA reaction to occur while in contact with the cured 3D printing materials as well as the residual autofluorescence and fluorescence drift [...] Read more.

We investigate the compatibility of three 3D printing materials towards real-time recombinase polymerase amplification (rtRPA). Both the general ability of the rtRPA reaction to occur while in contact with the cured 3D printing materials as well as the residual autofluorescence and fluorescence drift in dependence on post curing of the materials is characterized. We 3D printed monolithic rtRPA microreactors and subjected the devices to different post curing protocols. Residual autofluorescence and drift, as well as rtRPA kinetics, were then measured in a custom-made mobile temperature-controlled fluorescence reader (mTFR). Furthermore, we investigated the effects of storage on the devices over a 30-day period. Finally, we present the single- and duplex rtRPA detection of both the organism-specific Klebsiella haemolysin (khe) gene and the New Delhi metallo-β-lactamase 1 (bla_NDM-1) gene from Klebsiella pneumoniae. Results: No combination of 3D printing resin and post curing protocol completely inhibited the rtRPA reaction. The autofluorescence and fluorescence drift measured were found to be highly dependent on printing material and wavelength. Storage had the effect of decreasing the autofluorescence of the investigated materials. Both khe and bla_NDM-1 were successfully detected by single- and duplex-rtRPA inside monolithic rtRPA microreactors printed from NextDent Ortho Clear (NXOC). The reaction kinetics were found to be close to those observed for rtRPA performed in a microcentrifuge tube without the need for mixing during amplification. Singleplex assays for both khe and bla_NDM-1 achieved a limit of detection of 2.5 × 10¹ DNA copies while the duplex assay achieved 2.5 × 10¹ DNA copies for khe and 2.5 × 10² DNA copies for bla_NDM-1. Impact: We expand on the state of the art by demonstrating a technology that can manufacture monolithic microfluidic devices that are readily suitable for rtRPA. The devices exhibit very low autofluorescence and fluorescence drift and are compatible with RPA chemistry without the need for any surface pre-treatment such as blocking with, e.g., BSA or PEG. Full article

(This article belongs to the Section B：Biology and Biomedicine)

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17 pages, 2249 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optimal Control of Colloidal Trajectories in Inertial Microfluidics Using the Saffman Effect

by Felix Rühle, Christian Schaaf and Holger Stark

Micromachines 2020, 11(6), 592; https://doi.org/10.3390/mi11060592 - 15 Jun 2020

Cited by 5 | Viewed by 3264

Abstract

In inertial microfluidics colloidal particles in a Poiseuille flow experience the Segré-Silberberg lift force, which drives them to specific positions in the channel cross section. An external force applied along the microchannel induces a cross-streamline migration to a new equilibrium position because of [...] Read more.

In inertial microfluidics colloidal particles in a Poiseuille flow experience the Segré-Silberberg lift force, which drives them to specific positions in the channel cross section. An external force applied along the microchannel induces a cross-streamline migration to a new equilibrium position because of the Saffman effect. We apply optimal control theory to design the time protocol of the axial control force in order to steer a single particle as precisely as possible from a channel inlet to an outlet at a chosen target position. We discuss the influence of particle radius and channel length and show that optimal steering is cheaper than using a constant control force. Using a single optimized control-force protocol, we demonstrate that even a pulse of particles spread along the channel axis can be steered to a target and that particles of different radii can be separarted most efficiently. Full article

(This article belongs to the Special Issue Inertial Microfluidics)

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19 pages, 6235 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Droplet-Based Screening for the Investigation of Microbial Nonlinear Dose–Response Characteristics System, Background and Examples

by Jialan Cao, Felix Richter, Michael Kastl, Jonny Erdmann, Christian Burgold, David Dittrich, Steffen Schneider, J. Michael Köhler and G. Alexander Groß

Micromachines 2020, 11(6), 577; https://doi.org/10.3390/mi11060577 - 8 Jun 2020

Cited by 9 | Viewed by 3172

Abstract

Droplet-based microfluidics is a versatile tool to reveal the dose–response relationship of different effectors on the microbial proliferation. Traditional readout parameter is the temporal development of the cell density for different effector concentrations. To determine nonlinear or unconventional dose–response relationships, data with high [...] Read more.

Droplet-based microfluidics is a versatile tool to reveal the dose–response relationship of different effectors on the microbial proliferation. Traditional readout parameter is the temporal development of the cell density for different effector concentrations. To determine nonlinear or unconventional dose–response relationships, data with high temporal resolution and dense concentration graduation are essential. If microorganisms with slow microbial growth kinetics are investigated, a sterile and evaporation-free long-term incubation technique is required. Here, we present a modular droplet-based screening system which was developed to solve these issues. Beside relevant technical aspects of the developed modules, the procedural workflow, and exemplary dose–response data for 1D and 2D dose–response screenings are presented. Full article

(This article belongs to the Special Issue Microfluidic for High-Throughput Screening)

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12 pages, 1836 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Novel Design Approaches in the Fabrication of Polymeric Microarray Patches via Micromoulding

by Inken K. Ramöller, Emma McAlister, Abigail Bogan, Ana S. Cordeiro and Ryan F. Donnelly

Micromachines 2020, 11(6), 554; https://doi.org/10.3390/mi11060554 - 30 May 2020

Cited by 27 | Viewed by 4557

Abstract

The focus on novel systems for transdermal delivery of therapeutic agents has increased considerably over recent years, as this administration route comes with many advantages. Polymeric microarray patches (MAPs) are minimally invasive devices that enable systemic delivery of a wide range of drugs [...] Read more.

The focus on novel systems for transdermal delivery of therapeutic agents has increased considerably over recent years, as this administration route comes with many advantages. Polymeric microarray patches (MAPs) are minimally invasive devices that enable systemic delivery of a wide range of drugs by overcoming the outer skin barrier. Conventionally, MAPs fabricated by micromoulding have a low needle density. In this study, the performance of hydrogel-forming MAPs cast using novel industrially manufactured micromoulds with a high needle density (600 needles/0.75 cm²) was compared to that of MAPs obtained using conventional moulds with a lower density (196 needles/0.89 cm²). Surrounding holders for micromoulds were designed for time-efficient fabrication of MAPs. The influence of needle densities on mechanical strength, insertion efficiency and in vitro permeation of ibuprofen sodium (IBU) was analysed. Insertion of both MAPs into an artificial skin model and neonatal porcine skin was comparable. No significant difference was observed in permeation studies of IBU (p > 0.05), with a delivery of 8.7 ± 1.7 mg for low-density and 9.5 ± 0.1 mg for high-density MAPs within 24 h. This highlights the potential of these novel micromoulds for manufacturing polymeric MAPs with a higher needle density for future applications. Full article

(This article belongs to the Special Issue Microneedles)

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17 pages, 8494 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Sperm Cell Driven Microrobots—Emerging Opportunities and Challenges for Biologically Inspired Robotic Design

by Ajay Vikram Singh, Mohammad Hasan Dad Ansari, Mihir Mahajan, Shubhangi Srivastava, Shubham Kashyap, Prajjwal Dwivedi, Vaibhav Pandit and Uma Katha

Micromachines 2020, 11(4), 448; https://doi.org/10.3390/mi11040448 - 23 Apr 2020

Cited by 73 | Viewed by 13176

Abstract

With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are [...] Read more.

With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are the main challenges. Propulsion at micro-scale where the Reynolds number is very low is difficult. To overcome this, nature has developed flagella which have evolved over millions of years to work as a micromotor. Among the microscopic cells that exhibit this mode of propulsion, sperm cells are considered to be fast paced. Here, we give a brief review of the state-of-the-art of Spermbots—a new class of microrobots created by coupling sperm cells to mechanical loads. Spermbots utilize the flagellar movement of the sperm cells for propulsion and as such do not require any toxic fuel in their environment. They are also naturally biocompatible and show considerable speed of motion thereby giving us an option to overcome the two challenges of propulsion and biocompatibility. The coupling mechanisms of physical load to the sperm cells are discussed along with the advantages and challenges associated with the spermbot. A few most promising applications of spermbots are also discussed in detail. A brief discussion of the future outlook of this extremely promising category of microrobots is given at the end. Full article

(This article belongs to the Special Issue Advances in Microswimmers)

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14 pages, 3263 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High-Throughput Particle Concentration Using Complex Cross-Section Microchannels

by Asma Mihandoust, Sajad Razavi Bazaz, Nahid Maleki-Jirsaraei, Majid Alizadeh, Robert A. Taylor and Majid Ebrahimi Warkiani

Micromachines 2020, 11(4), 440; https://doi.org/10.3390/mi11040440 - 22 Apr 2020

Cited by 23 | Viewed by 4386

Abstract

High throughput particle/cell concentration is crucial for a wide variety of biomedical, clinical, and environmental applications. In this work, we have proposed a passive spiral microfluidic concentrator with a complex cross-sectional shape, i.e., a combination of rectangle and trapezoid, for high separation efficiency [...] Read more.

High throughput particle/cell concentration is crucial for a wide variety of biomedical, clinical, and environmental applications. In this work, we have proposed a passive spiral microfluidic concentrator with a complex cross-sectional shape, i.e., a combination of rectangle and trapezoid, for high separation efficiency and a confinement ratio less than 0.07. Particle focusing in our microfluidic system was observed in a single, tight focusing line, in which higher particle concentration is possible, as compared with simple rectangular or trapezoidal cross-sections with similar flow area. The sharper focusing stems from the confinement of Dean vortices in the trapezoidal region of the complex cross-section. To quantify this effect, we introduce a new parameter, complex focusing number or CFN, which is indicative of the enhancement of inertial focusing of particles in these channels. Three spiral microchannels with various widths of 400 µm, 500 µm, and 600 µm, with the corresponding CFNs of 4.3, 4.5, and 6, respectively, were used. The device with the total width of 600 µm was shown to have a separation efficiency of ~98%, and by recirculating, the output concentration of the sample was 500 times higher than the initial input. Finally, the investigation of results showed that the magnitude of CFN relies entirely on the microchannel geometry, and it is independent of the overall width of the channel cross-section. We envision that this concept of particle focusing through complex cross-sections will prove useful in paving the way towards more efficient inertial microfluidic devices. Full article

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14 pages, 3062 KiB

Open AccessFeature PaperEditor’s ChoicePerspective

3D Printed MEMS Technology—Recent Developments and Applications

by Tomasz Blachowicz and Andrea Ehrmann

Micromachines 2020, 11(4), 434; https://doi.org/10.3390/mi11040434 - 20 Apr 2020

Cited by 55 | Viewed by 11995

Abstract

Microelectromechanical systems (MEMS) are of high interest for recent electronic applications. Their applications range from medicine to measurement technology, from microfluidics to the Internet of Things (IoT). In many cases, MEMS elements serve as sensors or actuators, e.g., in recent mobile phones, but [...] Read more.

Microelectromechanical systems (MEMS) are of high interest for recent electronic applications. Their applications range from medicine to measurement technology, from microfluidics to the Internet of Things (IoT). In many cases, MEMS elements serve as sensors or actuators, e.g., in recent mobile phones, but also in future autonomously driving cars. Most MEMS elements are based on silicon, which is not deformed plastically under a load, as opposed to metals. While highly sophisticated solutions were already found for diverse MEMS sensors, actuators, and other elements, MEMS fabrication is less standardized than pure microelectronics, which sometimes blocks new ideas. One of the possibilities to overcome this problem may be the 3D printing approach. While most 3D printing technologies do not offer sufficient resolution for MEMS production, and many of the common 3D printing materials cannot be used for this application, there are still niches in which the 3D printing of MEMS enables producing new structures and thus creating elements for new applications, or the faster and less expensive production of common systems. Here, we give an overview of the most recent developments and applications in 3D printing of MEMS. Full article

(This article belongs to the Special Issue 3D Printing of MEMS Technology)

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14 pages, 3261 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Microfluidic-Based Investigation of Bacterial Attachment in Ureteral Stents

by Antonio De Grazia, Gareth LuTheryn, Alireza Meghdadi, Ali Mosayyebi, Erika J. Espinosa-Ortiz, Robin Gerlach and Dario Carugo

Micromachines 2020, 11(4), 408; https://doi.org/10.3390/mi11040408 - 13 Apr 2020

Cited by 23 | Viewed by 5508

Abstract

Obstructions of the ureter lumen can originate from intrinsic or extrinsic factors, such as kidney stones, tumours, or strictures. These can affect the physiological flow of urine from the kidneys to the bladder, potentially causing infection, pain, and kidney failure. To overcome these [...] Read more.

Obstructions of the ureter lumen can originate from intrinsic or extrinsic factors, such as kidney stones, tumours, or strictures. These can affect the physiological flow of urine from the kidneys to the bladder, potentially causing infection, pain, and kidney failure. To overcome these complications, ureteral stents are often deployed clinically in order to temporarily re-establish urinary flow. Despite their clinical benefits, stents are prone to encrustation and biofilm formation that lead to reduced quality of life for patients; however, the mechanisms underlying the formation of crystalline biofilms in stents are not yet fully understood. In this study, we developed microfluidic-based devices replicating the urodynamic field within different configurations of an occluded and stented ureter. We employed computational fluid dynamic simulations to characterise the flow dynamic field within these models and investigated bacterial attachment (Pseudomonas fluorescens) by means of crystal violet staining and fluorescence microscopy. We identified the presence of hydrodynamic cavities in the vicinity of a ureteric occlusion, which were characterised by low levels of wall shear stress (WSS < 40 mPa), and observed that initiation of bacterial attachment occurred in these specific regions of the stented ureter. Notably, the bacterial coverage area was directly proportional to the number of cavities present in the model. Fluorescence microscopy confirmed that the number density of bacteria was greater within cavities (3 bacteria·mm⁻²) when compared to side-holes of the stent (1 bacterium·mm⁻²) or its luminal surface (0.12 bacteria·mm⁻²). These findings informed the design of a novel technological solution against bacterial attachment, which reduces the extent of cavity flow and increases wall shear stress over the stent’s surface. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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15 pages, 3964 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Controllable pH Manipulations in Micro/Nanofluidic Device Using Nanoscale Electrokinetics

by Jae Suk Park, Jeewhan Oh and Sung Jae Kim

Micromachines 2020, 11(4), 400; https://doi.org/10.3390/mi11040400 - 10 Apr 2020

Cited by 6 | Viewed by 3034

Abstract

Recently introduced nanoscale electrokinetic phenomenon called ion concentration polarization (ICP) has been suffered from serious pH changes to the sample fluid. A number of studies have focused on the origin of pH changes and strategies for regulating it. Instead of avoiding pH changes, [...] Read more.

Recently introduced nanoscale electrokinetic phenomenon called ion concentration polarization (ICP) has been suffered from serious pH changes to the sample fluid. A number of studies have focused on the origin of pH changes and strategies for regulating it. Instead of avoiding pH changes, in this work, we tried to demonstrate new ways to utilize this inevitable pH change. First, one can obtain a well-defined pH gradient in proton-received microchannel by applying a fixed electric current through a proton exchange membrane. Furthermore, one can tune the pH gradient on demand by adjusting the proton mass transportation (i.e., adjusting electric current). Secondly, we demonstrated that the occurrence of ICP can be examined by sensing a surrounding pH of electrolyte solution. When pH > threshold pH, patterned pH-responsive hydrogel inside a straight microchannel acted as a nanojunction to block the microchannel, while it did as a microjunction when pH < threshold pH. In case of forming a nanojunction, electrical current significantly dropped compared to the case of a microjunction. The strategies that presented in this work would be a basis for useful engineering applications such as a localized pH stimulation to biomolecules using tunable pH gradient generation and portable pH sensor with pH-sensitive hydrogel. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

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17 pages, 10037 KiB

Open AccessEditor’s ChoiceArticle

Construction of a CQDs/Ag₃PO₄/BiPO₄ Heterostructure Photocatalyst with Enhanced Photocatalytic Degradation of Rhodamine B under Simulated Solar Irradiation

by Huajing Gao, Chengxiang Zheng, Hua Yang, Xiaowei Niu and Shifa Wang

Micromachines 2019, 10(9), 557; https://doi.org/10.3390/mi10090557 - 23 Aug 2019

Cited by 57 | Viewed by 5115

Abstract

A carbon quantum dot (CQDs)/Ag₃PO₄/BiPO₄ heterostructure photocatalyst was constructed by a simple hydrothermal synthesis method. The as-prepared CQDs/Ag₃PO₄/BiPO₄ photocatalyst has been characterized in detail by X-ray diffraction, field-emission scanning electron microscopy, transmission electron [...] Read more.

A carbon quantum dot (CQDs)/Ag₃PO₄/BiPO₄ heterostructure photocatalyst was constructed by a simple hydrothermal synthesis method. The as-prepared CQDs/Ag₃PO₄/BiPO₄ photocatalyst has been characterized in detail by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, and photoelectrochemical measurements. It is demonstrated that the CQDs/Ag₃PO₄/BiPO₄ composite is constructed by assembling Ag₃PO₄ fine particles and CQDs on the surface of rice-like BiPO₄ granules. The CQDs/Ag₃PO₄/BiPO₄ heterostructure photocatalyst exhibits a higher photocatalytic activity for the degradation of the rhodamine B dye than that of Ag₃PO₄, BiPO₄, and Ag₃PO₄/BiPO₄. The synergistic effects of light absorption capacity, band edge position, separation, and utilization efficiency of photogenerated carriers play the key role for the enhanced photodegradation of the rhodamine B dye. Full article

(This article belongs to the Special Issue Nanostructures for Photocatalysis)

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15 pages, 13069 KiB

Open AccessEditor’s ChoiceArticle

Facile Preparation of CNT/Ag₂S Nanocomposites with Improved Visible and NIR Light Photocatalytic Degradation Activity and Their Catalytic Mechanism

by Lijing Di, Tao Xian, Xiaofeng Sun, Hongqin Li, Yongjie Zhou, Jun Ma and Hua Yang

Micromachines 2019, 10(8), 503; https://doi.org/10.3390/mi10080503 - 30 Jul 2019

Cited by 52 | Viewed by 4815

Abstract

In this work, a series of carbon nanotubes (CNT)/Ag₂S hybrid nanocomposites were successfully prepared by a facile precipitation method. Transmission electron microscope (TEM) observation indicates that Ag₂S nanoparticles with an average particle size of ~25 nm are uniformly anchored [...] Read more.

In this work, a series of carbon nanotubes (CNT)/Ag₂S hybrid nanocomposites were successfully prepared by a facile precipitation method. Transmission electron microscope (TEM) observation indicates that Ag₂S nanoparticles with an average particle size of ~25 nm are uniformly anchored on the surface of CNT. The photocatalytic activities of the CNT/Ag₂S nanocomposites were investigated toward the degradation of rhodamine B (RhB) under visible and near-infrared (NIR) light irradiation. It is shown that the nanocomposites exhibit obviously enhanced visible and NIR light photocatalytic activities compared with bare Ag₂S nanoparticles. Moreover, the recycling photocatalytic experiment demonstrates that the CNT/Ag₂S nanocomposites possess excellent photocatalytic stability. The photoelectrochemical and photoluminescence measurements reveal the efficient separation of photogenerated charges in the CNT/Ag₂S nanocomposites. This is the dominant reason behind the improvement of the photocatalytic activity. Based on active species trapping experiments, the possible photocatalytic mechanism of CNT/Ag₂S nanocomposites for dye degradation under visible and NIR light irradiation was proposed. Full article

(This article belongs to the Section D：Materials and Processing)

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11 pages, 4881 KiB

Open AccessEditor’s ChoiceArticle

Dual-Band Plasmonic Perfect Absorber Based on Graphene Metamaterials for Refractive Index Sensing Application

by Zao Yi, Cuiping Liang, Xifang Chen, Zigang Zhou, Yongjian Tang, Xin Ye, Yougen Yi, Junqiao Wang and Pinghui Wu

Micromachines 2019, 10(7), 443; https://doi.org/10.3390/mi10070443 - 2 Jul 2019

Cited by 99 | Viewed by 5511

Abstract

We demonstrate a dual-band plasmonic perfect absorber (PA) based on graphene metamaterials. Two absorption peaks (22.5 μm and 74.5 μm) with the maximal absorption of 99.4% and 99.9% have been achieved, respectively. We utilize this perfect absorber as a plasmonic sensor for refractive [...] Read more.

We demonstrate a dual-band plasmonic perfect absorber (PA) based on graphene metamaterials. Two absorption peaks (22.5 μm and 74.5 μm) with the maximal absorption of 99.4% and 99.9% have been achieved, respectively. We utilize this perfect absorber as a plasmonic sensor for refractive index (RI) sensing. It has the figure of merit (FOM) of 10.8 and 3.2, and sensitivities of about 5.6 and 17.2 μm/RIU, respectively. Hence, the designed dual-band PA-based RI sensor exhibits good sensing performance in the infrared regime, which offers great potential applications in various biomedical, tunable spectral detecting, environmental monitoring and medical diagnostics. Full article

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10 pages, 1831 KiB

Open AccessEditor’s ChoiceArticle

Effects of Charge Transport Materials on Blue Fluorescent Organic Light-Emitting Diodes with a Host-Dopant System

by Neng Liu, Sijiong Mei, Dongwei Sun, Wuxing Shi, Jiahuan Feng, Yuanming Zhou, Fei Mei, Jinxia Xu, Yan Jiang and Xianan Cao

Micromachines 2019, 10(5), 344; https://doi.org/10.3390/mi10050344 - 25 May 2019

Cited by 78 | Viewed by 6976

Abstract

High efficiency blue fluorescent organic light-emitting diodes (OLEDs), based on 1,3-bis(carbazol-9-yl)benzene (mCP) doped with 4,4’-bis(9-ethyl-3-carbazovinylene)-1,1’-biphenyl (BCzVBi), were fabricated using four different hole transport layers (HTLs) and two different electron transport layers (ETLs). Fixing the electron transport material TPBi, four hole transport materials, including [...] Read more.

High efficiency blue fluorescent organic light-emitting diodes (OLEDs), based on 1,3-bis(carbazol-9-yl)benzene (mCP) doped with 4,4’-bis(9-ethyl-3-carbazovinylene)-1,1’-biphenyl (BCzVBi), were fabricated using four different hole transport layers (HTLs) and two different electron transport layers (ETLs). Fixing the electron transport material TPBi, four hole transport materials, including 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), N,N’-Di(1-naphthyl)-N,N’-diphenyl-(1,1’-biphenyl)-4’-diamine(NPB), 4,4’-Bis(N-carbazolyl)-1,1,-biphenyl (CBP) and molybdenum trioxide (MoO₃), were selected to be HTLs, and the blue OLED with TAPC HTL exhibited a maximum luminance of 2955 cd/m² and current efficiency (CE) of 5.75 cd/A at 50 mA/cm², which are 68% and 62% higher, respectively, than those of the minimum values found in the device with MoO₃ HTL. Fixing the hole transport material TAPC, the replacement of TPBi ETL with Bphen ETL can further improve the performance of the device, in which the maximum luminance can reach 3640 cd/m² at 50 mA/cm², which is 23% higher than that of the TPBi device. Furthermore, the lifetime of the device is also optimized by the change of ETL. These results indicate that the carrier mobility of transport materials and energy level alignment of different functional layers play important roles in the performance of the blue OLEDs. The findings suggest that selecting well-matched electron and hole transport materials is essential and beneficial for the device engineering of high-efficiency blue OLEDs. Full article

(This article belongs to the Special Issue Nanostructured Light-Emitters)

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16 pages, 22489 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Enhanced Photocatalytic Performance and Mechanism of Au@CaTiO₃ Composites with Au Nanoparticles Assembled on CaTiO₃ Nanocuboids

by Yuxiang Yan, Hua Yang, Zao Yi, Ruishan Li and Xiangxian Wang

Micromachines 2019, 10(4), 254; https://doi.org/10.3390/mi10040254 - 17 Apr 2019

Cited by 72 | Viewed by 5919

Abstract

Using P25 as the titanium source and based on a hydrothermal route, we have synthesized CaTiO₃ nanocuboids (NCs) with the width of 0.3–0.5 μm and length of 0.8–1.1 μm, and systematically investigated their growth process. Au nanoparticles (NPs) of 3–7 nm in [...] Read more.

Using P25 as the titanium source and based on a hydrothermal route, we have synthesized CaTiO₃ nanocuboids (NCs) with the width of 0.3–0.5 μm and length of 0.8–1.1 μm, and systematically investigated their growth process. Au nanoparticles (NPs) of 3–7 nm in size were assembled on the surface of CaTiO₃ NCs via a photocatalytic reduction method to achieve excellent Au@CaTiO₃ composite photocatalysts. Various techniques were used to characterize the as-prepared samples, including X-ray powder diffraction (XRD), scanning/transmission electron microscopy (SEM/TEM), diffuse reflectance spectroscopy (UV-vis DRS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Rhodamine B (RhB) in aqueous solution was chosen as the model pollutant to assess the photocatalytic performance of the samples separately under simulated-sunlight, ultraviolet (UV) and visible-light irradiation. Under irradiation of all kinds of light sources, the Au@CaTiO₃ composites, particularly the 4.3%Au@CaTiO₃ composite, exhibit greatly enhanced photocatalytic performance when compared with bare CaTiO₃ NCs. The main roles of Au NPs in the enhanced photocatalytic mechanism of the Au@CaTiO₃ composites manifest in the following aspects: (1) Au NPs act as excellent electron sinks to capture the photoexcited electrons in CaTiO₃, thus leading to an efficient separation of photoexcited electron/hole pairs in CaTiO₃; (2) the electromagnetic field caused by localized surface plasmon resonance (LSPR) of Au NPs could facilitate the generation and separation of electron/hole pairs in CaTiO₃; and (3) the LSPR-induced electrons in Au NPs could take part in the photocatalytic reactions. Full article

(This article belongs to the Special Issue Nanostructures for Photocatalysis)

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11 pages, 2585 KiB

Open AccessEditor’s ChoiceArticle

Tunable Graphene-based Plasmonic Perfect Metamaterial Absorber in the THz Region

by Zao Yi, Jiajia Chen, Chunlian Cen, Xifang Chen, Zigang Zhou, Yongjian Tang, Xin Ye, Shuyuan Xiao, Wei Luo and Pinghui Wu

Micromachines 2019, 10(3), 194; https://doi.org/10.3390/mi10030194 - 18 Mar 2019

Cited by 75 | Viewed by 6483

Abstract

The optical performance of a periodically tunable plasma perfect metamaterial absorber based on a square-square-circle array we propose in the terahertz region is analyzed in this work by the finite difference time domain (FDTD) method. We not only discuss the impact of various [...] Read more.

The optical performance of a periodically tunable plasma perfect metamaterial absorber based on a square-square-circle array we propose in the terahertz region is analyzed in this work by the finite difference time domain (FDTD) method. We not only discuss the impact of various parameters such as period a, length L, radius R, and incident angle θ under transverse magnetic (TM)- and transverse electric (TE)-polarization on the absorption spectra of the absorber but also study the effect of the Fermi energy E_F and relaxation time τ. Finally, we simulate the spectra as the surrounding refractive index n changes to better evaluate the sensing performance of the structure, producing a sensitivity S of the structure of up to 15006 nm/RIU. On account of this research, we find that the absorber is beneficial to sensors and detectors in the terahertz region. Full article

(This article belongs to the Special Issue Plasmonics: From Materials to Devices)

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13 pages, 3934 KiB

Open AccessEditor’s ChoiceArticle

Fabriction of ZnO Nanorods with Strong UV Absorption and Different Hydrophobicity on Foamed Nickel under Different Hydrothermal Conditions

by Xin Li, Xifang Chen, Zao Yi, Zigang Zhou, Yongjian Tang and Yougen Yi

Micromachines 2019, 10(3), 164; https://doi.org/10.3390/mi10030164 - 27 Feb 2019

Cited by 46 | Viewed by 4615

Abstract

ZnO nanorods have been grown on the surface of foamed nickel by a two-step method. Firstly, a layer of ZnO seed is sputtered on the surface of the foamed nickel by magnetron sputtering, and then the hydrothermal method is used to grow ZnO [...] Read more.

ZnO nanorods have been grown on the surface of foamed nickel by a two-step method. Firstly, a layer of ZnO seed is sputtered on the surface of the foamed nickel by magnetron sputtering, and then the hydrothermal method is used to grow ZnO nanorods at different conditions (solution concentration, reaction time and reaction temperature). The results show that the morphology of ZnO nanorods is closely related to the solution concentration, reaction time, and reaction temperature. The energy band structure formed by the foamed nickel and ZnO seed layers and the growth mechanism of ZnO nanorods are discussed. The samples are characterized by Energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and Raman spectroscopy. The absorption characteristics of samples to light are characterized by ultraviolet-to-visible (UV–VIS) absorption. The hydrophilicity of the samples is characterized by the static contact angle. By analyzing the performance characteristics of the samples at different conditions, we finally obtained the optimal growth parameters. At the optimal parameters, the morphology of the grown nanorods is regular, the ultraviolet band has strong absorption, and the surface of the samples forms a superhydrophobic surface. Full article

(This article belongs to the Special Issue Nanowires and Nanoprobes – Functionalized Arrays)

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18 pages, 7708 KiB

Open AccessEditor’s ChoiceArticle

Growth Process and CQDs-modified Bi₄Ti₃O₁₂ Square Plates with Enhanced Photocatalytic Performance

by Xinxin Zhao, Hua Yang, Ziming Cui, Xiangxian Wang and Zao Yi

Micromachines 2019, 10(1), 66; https://doi.org/10.3390/mi10010066 - 18 Jan 2019

Cited by 43 | Viewed by 4803

Abstract

Bi₄Ti₃O₁₂ square plates were synthesized via a hydrothermal route, and their growth process was systematically investigated. Carbon quantum dots (CQDs) were prepared using glucose as the carbon source, which were then assembled on the surface of Bi₄ [...] Read more.

Bi₄Ti₃O₁₂ square plates were synthesized via a hydrothermal route, and their growth process was systematically investigated. Carbon quantum dots (CQDs) were prepared using glucose as the carbon source, which were then assembled on the surface of Bi₄Ti₃O₁₂ square plates via a hydrothermal route with the aim of enhancing the photocatalytic performance. XRD (X-ray powder diffraction), SEM (scanning electron microscopy), TEM (transmission electron microscopy), UV-vis DRS (diffuse reflectance spectroscopy), XPS (X-ray photoelectron spectroscopy), FTIR (Fourier transform infrared spectroscopy), PL (photoluminescence) spectroscopy, EIS (electrochemical impedance spectroscopy) and photocurrent spectroscopy were used to systematically characterize the as-prepared samples. It is demonstrated that the decoration of CQDs on Bi₄Ti₃O₁₂ plates leads to an increased visible light absorption, slightly increased bandgap, increased photocurrent density, decreased charge-transfer resistance, and decreased PL intensity. Simulated sunlight and visible light were separately used as a light source to evaluate the photocatalytic activity of the samples toward the degradation of RhB in aqueous solution. Under both simulated sunlight and visible light irradiation, CQDs@Bi₄Ti₃O₁₂ composites with an appropriate amount of CQDs exhibit obviously enhanced photocatalytic performance. However, the decoration of excessive CQDs gives rise to a decrease in the photocatalytic activity. The enhanced photocatalytic activity of CQDs-modified Bi₄Ti₃O₁₂ can be attributed to the following reasons: (1) The electron transfer between Bi₄Ti₃O₁₂ and CQDs promotes an efficient separation of photogenerated electron/hole pairs in Bi₄Ti₃O₁₂; (2) the up-conversion photoluminescence emitted from CQDs could induce the generation of additional electron/hole pairs in Bi₄Ti₃O₁₂; and (3) the photoexcited electrons in CQDs could participate in the photocatalytic reactions. Full article

(This article belongs to the Special Issue Nanostructures for Photocatalysis)

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