Micromachines

14 pages, 3318 KiB

Open AccessArticle

Electrochemical Performance of Micropillar Array Electrodes in Microflows

by Bo Liu, Chuanwen Lv, Chaozhan Chen, Bin Ran, Minbo Lan, Huaying Chen and Yonggang Zhu

Micromachines 2020, 11(9), 858; https://doi.org/10.3390/mi11090858 - 17 Sep 2020

Cited by 11 | Viewed by 3143

The microchip-based electrochemical detection system (μEDS) has attracted plenty of research attention due to its merits including the capability in high-density integration, high sensitivity, fast analysis time, and reduced reagent consumption. The miniaturized working electrode is usually regarded as the core component of [...] Read more.

The microchip-based electrochemical detection system (μEDS) has attracted plenty of research attention due to its merits including the capability in high-density integration, high sensitivity, fast analysis time, and reduced reagent consumption. The miniaturized working electrode is usually regarded as the core component of the μEDS, since its characteristic directly determines the performance of the whole system. Compared with the microelectrodes with conventional shapes such as the band, ring and disk, the three-dimensional (3D) micropillar array electrode (μAE) has demonstrated significant potential in improving the current response and decreasing the limits of detection due to its much larger reaction area. In this study, the numerical simulation method was used to investigate the performance of the μEDS, and both the geometrical and hydrodynamic parameters, including the micropillars shape, height, arrangement form and the flow rate of the reactant solution, were taken into consideration. The tail effect in μAEs was also quantitatively analyzed based on a pre-defined parameter of the current density ratio. In addition, a PDMS-based 3D μAE was fabricated and integrated into the microchannel for the electrochemical detection. The experiments of cyclic voltammetry (CV) and chronoamperometry (CA) were conducted, and a good agreement was found between the experimental and simulation results. This study would be instructive for the configuration and parameters design of the μEDS, and the presented method can be adopted to analyze and optimize the performance of nanochip-based electrochemical detection system (nEDS). Full article

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

► Show Figures

Figure 1

11 pages, 2549 KiB

Open AccessArticle

Fabrication of Infrared-Compatible Nanofluidic Devices for Plasmon-Enhanced Infrared Absorption Spectroscopy

by Thu Hac Huong Le, Takumi Matsushita, Ryoichi Ohta, Yuta Shimoda, Hiroaki Matsui and Takehiko Kitamori

Micromachines 2020, 11(12), 1062; https://doi.org/10.3390/mi11121062 - 30 Nov 2020

Cited by 2 | Viewed by 2122

Abstract

Nanofluidic devices have offered us fascinating analytical platforms for chemical and bioanalysis by exploiting unique properties of liquids and molecules confined in nanospaces. The increasing interests in nanofluidic analytical devices have triggered the development of new robust and sensitive detection techniques, especially label-free [...] Read more.

Nanofluidic devices have offered us fascinating analytical platforms for chemical and bioanalysis by exploiting unique properties of liquids and molecules confined in nanospaces. The increasing interests in nanofluidic analytical devices have triggered the development of new robust and sensitive detection techniques, especially label-free ones. IR absorption spectroscopy is one of the most powerful biochemical analysis methods for identification and quantitative measurement of chemical species in the label-free and non-invasive fashion. However, the low sensitivity and the difficulties in fabrication of IR-compatible nanofluidic devices are major obstacles that restrict the applications of IR spectroscopy in nanofluidics. Here, we realized the bonding of CaF₂ and SiO₂ at room temperature and demonstrated an IR-compatible nanofluidic device that allowed the IR spectroscopy in a wide range of mid-IR regime. We also performed the integration of metal-insulator-metal perfect absorber metamaterials into nanofluidic devices for plasmon-enhanced infrared absorption spectroscopy with ultrahigh sensitivity. This study also shows a proof-of-concept of the multi-band absorber by combining different types of nanostructures. The results indicate the potential of implementing metamaterials in tracking several characteristic molecular vibrational modes simultaneously, making it possible to identify molecular species in mixture or complex biological entities. Full article

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

► Show Figures

Figure 1

12 pages, 3312 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Joule Heating Effects on Transport-Induced-Charge Phenomena in an Ultrathin Nanopore

by Zhixuan Wang, Wei-Lun Hsu, Shuntaro Tsuchiya, Soumyadeep Paul, Amer Alizadeh and Hirofumi Daiguji

Micromachines 2020, 11(12), 1041; https://doi.org/10.3390/mi11121041 - 26 Nov 2020

Cited by 8 | Viewed by 3280

Abstract

Transport-induced-charge (TIC) phenomena, in which the concentration imbalance between cations and anions occurs when more than two chemical potential gradients coexist within an ultrathin dimension, entail numerous nanofluidic systems. Evidence has indicated that the presence of TIC produces a nonlinear response of electroosmotic [...] Read more.

Transport-induced-charge (TIC) phenomena, in which the concentration imbalance between cations and anions occurs when more than two chemical potential gradients coexist within an ultrathin dimension, entail numerous nanofluidic systems. Evidence has indicated that the presence of TIC produces a nonlinear response of electroosmotic flow to the applied voltage, resulting in complex fluid behavior. In this study, we theoretically investigate thermal effects due to Joule heating on TIC phenomena in an ultrathin nanopore by computational fluid dynamics simulation. Our modeling results show that the rise of local temperature inside the nanopore significantly enhances TIC effects and thus has a significant influence on electroosmotic behavior. A local maximum of the solution conductivity occurs near the entrance of the nanopore at the high salt concentration end, resulting in a reversal of TIC across the nanopore. The Joule heating effects increase the reversal of TIC with the synergy of the negatively charged nanopore, and they also enhance the electroosmotic flow regardless of whether the nanopore is charged. These theoretical observations will improve our knowledge of nonclassical electrokinetic phenomena for flow control in nanopore systems. Full article

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

► Show Figures

Graphical abstract

14 pages, 1902 KiB

Open AccessArticle

Single-Molecule Counting of Nucleotide by Electrophoresis with Nanochannel-Integrated Nano-Gap Devices

by Takahito Ohshiro, Yuki Komoto and Masateru Taniguchi

Micromachines 2020, 11(11), 982; https://doi.org/10.3390/mi11110982 - 31 Oct 2020

Cited by 9 | Viewed by 2440

Abstract

We utilized electrophoresis to control the fluidity of sample biomolecules in sample aqueous solutions inside the nanochannel for single-molecule detection by using a nanochannel-integrated nanogap electrode, which is composed of a nano-gap sensing electrode, nanochannel, and tapered focusing channel. In order to suppress [...] Read more.

We utilized electrophoresis to control the fluidity of sample biomolecules in sample aqueous solutions inside the nanochannel for single-molecule detection by using a nanochannel-integrated nanogap electrode, which is composed of a nano-gap sensing electrode, nanochannel, and tapered focusing channel. In order to suppress electro-osmotic flow and thermal convection inside this nanochannel, we optimized the reduction ratios of the tapered focusing channel, and the ratio of inlet 10 μm to outlet 0.5 μm was found to be high performance of electrophoresis with lower concentration of 0.05 × TBE (Tris/Borate/EDTA) buffer containing a surfactant of 0.1 w/v% polyvinylpyrrolidone (PVP). Under the optimized conditions, single-molecule electrical measurement of deoxyguanosine monophosphate (dGMP) was performed and it was found that the throughput was significantly improved by nearly an order of magnitude compared to that without electrophoresis. In addition, it was also found that the long-duration signals that could interfere with discrimination were significantly reduced. This is because the strong electrophoresis flow inside the nanochannels prevents the molecules’ adsorption near the electrodes. This single-molecule electrical measurement with nanochannel-integrated nano-gap electrodes by electrophoresis significantly improved the throughput of signal detection and identification accuracy. Full article

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

► Show Figures

Figure 1

13 pages, 10249 KiB

Open AccessArticle

Pore Structures for High-Throughput Nanopore Devices

by Sou Ryuzaki, Rintaro Matsuda and Masateru Taniguchi

Micromachines 2020, 11(10), 893; https://doi.org/10.3390/mi11100893 - 26 Sep 2020

Cited by 1 | Viewed by 2473

Abstract

Nanopore devices are expected to advance the next-generation of nanobiodevices because of their strong sensing and analyzing capabilities for single molecules and bioparticles. However, the device throughputs are not sufficiently high. Although analytes pass through a nanopore by electrophoresis, the electric field gradient [...] Read more.

Nanopore devices are expected to advance the next-generation of nanobiodevices because of their strong sensing and analyzing capabilities for single molecules and bioparticles. However, the device throughputs are not sufficiently high. Although analytes pass through a nanopore by electrophoresis, the electric field gradient is localized inside and around a nanopore structure. Thus, analytes located far from a nanopore cannot be driven by electrophoresis. Here, we report nanopore structures for high-throughput sensing, namely, inverted pyramid (IP)-shaped nanopore structures. Silicon-based IP-shaped nanopore structures create a homogeneous electric field gradient within a nanopore device, indicating that most of the analytes can pass through a nanopore by electrophoresis, even though the analytes are suspended far from the nanopore entrance. In addition, the nanostructures can be fabricated only by photolithography. The present study suggests a high potential for inverted pyramid shapes to serve as nanopore devices for high-throughput sensing. Full article

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

► Show Figures

Graphical abstract

12 pages, 2137 KiB

Open AccessArticle

Mechanical Rupture-Based Antibacterial and Cell-Compatible ZnO/SiO₂ Nanowire Structures Formed by Bottom-Up Approaches

by Taisuke Shimada, Takao Yasui, Akihiro Yonese, Takeshi Yanagida, Noritada Kaji, Masaki Kanai, Kazuki Nagashima, Tomoji Kawai and Yoshinobu Baba

Micromachines 2020, 11(6), 610; https://doi.org/10.3390/mi11060610 - 24 Jun 2020

Cited by 16 | Viewed by 3934

Abstract

There are growing interests in mechanical rupture-based antibacterial surfaces with nanostructures that have little toxicity to cells around the surfaces; however, current surfaces are fabricated via top-down nanotechnologies, which presents difficulties to apply for bio-surfaces with hierarchal three-dimensional structures. Herein, we developed ZnO/SiO [...] Read more.

There are growing interests in mechanical rupture-based antibacterial surfaces with nanostructures that have little toxicity to cells around the surfaces; however, current surfaces are fabricated via top-down nanotechnologies, which presents difficulties to apply for bio-surfaces with hierarchal three-dimensional structures. Herein, we developed ZnO/SiO₂ nanowire structures by using bottom-up approaches and demonstrated to show mechanical rupture-based antibacterial activity and compatibility with human cells. When Escherichia coli were cultured on the surface for 24 h, over 99% of the bacteria were inactivated, while more than 80% of HeLa cells that were cultured on the surface for 24 h were still alive. This is the first demonstration of mechanical rupture-based bacterial rupture via the hydrothermally synthesized nanowire structures with antibacterial activity and cell compatibility. Full article

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

► Show Figures

Figure 1

21 pages, 3226 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Advances in Label-Free Detections for Nanofluidic Analytical Devices

by Thu Hac Huong Le, Hisashi Shimizu and Kyojiro Morikawa

Micromachines 2020, 11(10), 885; https://doi.org/10.3390/mi11100885 - 23 Sep 2020

Cited by 17 | Viewed by 3731

Abstract

Nanofluidics, a discipline of science and engineering of fluids confined to structures at the 1–1000 nm scale, has experienced significant growth over the past decade. Nanofluidics have offered fascinating platforms for chemical and biological analyses by exploiting the unique characteristics of liquids and [...] Read more.

Nanofluidics, a discipline of science and engineering of fluids confined to structures at the 1–1000 nm scale, has experienced significant growth over the past decade. Nanofluidics have offered fascinating platforms for chemical and biological analyses by exploiting the unique characteristics of liquids and molecules confined in nanospaces; however, the difficulty to detect molecules in extremely small spaces hampers the practical applications of nanofluidic devices. Laser-induced fluorescence microscopy with single-molecule sensitivity has been so far a major detection method in nanofluidics, but issues arising from labeling and photobleaching limit its application. Recently, numerous label-free detection methods have been developed to identify and determine the number of molecules, as well as provide chemical, conformational, and kinetic information of molecules. This review focuses on label-free detection techniques designed for nanofluidics; these techniques are divided into two groups: optical and electrical/electrochemical detection methods. In this review, we discuss on the developed nanofluidic device architectures, elucidate the mechanisms by which the utilization of nanofluidics in manipulating molecules and controlling light–matter interactions enhances the capabilities of biological and chemical analyses, and highlight new research directions in the field of detections in nanofluidics. Full article

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

► Show Figures

Figure 1

11 pages, 2180 KiB

Open AccessFeature PaperArticle

Size Sorting of Exosomes by Tuning the Thicknesses of the Electric Double Layers on a Micro-Nanofluidic Device

by Satoko Fujiwara, Kyojiro Morikawa, Tatsuro Endo, Hideaki Hisamoto and Kenji Sueyoshi

Micromachines 2020, 11(5), 458; https://doi.org/10.3390/mi11050458 - 28 Apr 2020

Cited by 12 | Viewed by 3594

Abstract

Exosomes, a type of extracellular vesicle with a diameter of 30–150 nm, perform key biological functions such as intercellular communication. Recently, size sorting of exosomes has received increasing attention in order to clarify the correlation between their size and components. However, such sorting [...] Read more.

Exosomes, a type of extracellular vesicle with a diameter of 30–150 nm, perform key biological functions such as intercellular communication. Recently, size sorting of exosomes has received increasing attention in order to clarify the correlation between their size and components. However, such sorting remains extremely difficult. Here, we propose to sort their size by controlling their electrokinetic migration in nanochannels in a micro-nanofluidic device, which is achieved by tuning the thickness of the electric double layers in the nanochannels. This approach was demonstrated experimentally for exosomes smaller than 250 nm. Using different running buffer concentrations (1 × 10⁻³, 1 × 10⁻⁴, and 1 × 10⁻⁵ M), most of the exosomes larger than 140, 110, and 80 nm were successfully cut off at the downstream of the nanochannels, respectively. Therefore, it is clarified that the proposed method is applicable for the size sorting of exosomes. Full article

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

► Show Figures

Graphical abstract

12 pages, 2194 KiB

Open AccessArticle

A Simple Low-Temperature Glass Bonding Process with Surface Activation by Oxygen Plasma for Micro/Nanofluidic Devices

by Koki Shoda, Minori Tanaka, Kensuke Mino and Yutaka Kazoe

Micromachines 2020, 11(9), 804; https://doi.org/10.3390/mi11090804 - 25 Aug 2020

Cited by 16 | Viewed by 4656

Abstract

The bonding of glass substrates is necessary when constructing micro/nanofluidic devices for sealing micro- and nanochannels. Recently, a low-temperature glass bonding method utilizing surface activation with plasma was developed to realize micro/nanofluidic devices for various applications, but it still has issues for general [...] Read more.

The bonding of glass substrates is necessary when constructing micro/nanofluidic devices for sealing micro- and nanochannels. Recently, a low-temperature glass bonding method utilizing surface activation with plasma was developed to realize micro/nanofluidic devices for various applications, but it still has issues for general use. Here, we propose a simple process of low-temperature glass bonding utilizing typical facilities available in clean rooms and applied it to the fabrication of micro/nanofluidic devices made of different glasses. In the process, the substrate surface was activated with oxygen plasma, and the glass substrates were placed in contact in a class ISO 5 clean room. The pre-bonded substrates were heated for annealing. We found an optimal concentration of oxygen plasma and achieved a bonding energy of 0.33–0.48 J/m² in fused-silica/fused-silica glass bonding. The process was applied to the bonding of fused-silica glass and borosilicate glass, which is generally used in optical microscopy, and revealed higher bonding energy than fused-silica/fused-silica glass bonding. An annealing temperature lower than 200 °C was necessary to avoid crack generation by thermal stress due to the different thermal properties of the glasses. A fabricated micro/nanofluidic device exhibited a pressure resistance higher than 600 kPa. This work will contribute to the advancement of micro/nanofluidics. Full article

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

► Show Figures

Figure 1

3 pages, 159 KiB

Open AccessEditorial

Advances in Nanofluidics

by Yutaka Kazoe and Yan Xu

Micromachines 2021, 12(4), 427; https://doi.org/10.3390/mi12040427 - 14 Apr 2021

Cited by 4 | Viewed by 2080

Abstract

Recently, a new frontier in fluid science and engineering at the 1 to 1000 nm scale, called nanofluidics, has developed and provided new methodologies and applications to the fields of chemistry, biology, material sciences, bioengineering, medicine, drug discovery, energy, and environmental engineering [...] [...] Read more.

Recently, a new frontier in fluid science and engineering at the 1 to 1000 nm scale, called nanofluidics, has developed and provided new methodologies and applications to the fields of chemistry, biology, material sciences, bioengineering, medicine, drug discovery, energy, and environmental engineering [...] Full article

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

11 pages, 2767 KiB

Open AccessArticle

Advanced Top-Down Fabrication for a Fused Silica Nanofluidic Device

by Kyojiro Morikawa, Yutaka Kazoe, Yuto Takagi, Yoshiyuki Tsuyama, Yuriy Pihosh, Takehiko Tsukahara and Takehiko Kitamori

Micromachines 2020, 11(11), 995; https://doi.org/10.3390/mi11110995 - 09 Nov 2020

Cited by 33 | Viewed by 3107

Abstract

Nanofluidics have recently attracted significant attention with regard to the development of new functionalities and applications, and producing new functional devices utilizing nanofluidics will require the fabrication of nanochannels. Fused silica nanofluidic devices fabricated by top-down methods are a promising approach to realizing [...] Read more.

Nanofluidics have recently attracted significant attention with regard to the development of new functionalities and applications, and producing new functional devices utilizing nanofluidics will require the fabrication of nanochannels. Fused silica nanofluidic devices fabricated by top-down methods are a promising approach to realizing this goal. Our group previously demonstrated the analysis of a living single cell using such a device, incorporating nanochannels having different sizes (10²–10³ nm) and with branched and confluent structures and surface patterning. However, fabrication of geometrically-controlled nanochannels on the 10¹ nm size scale by top-down methods on a fused silica substrate, and the fabrication of micro-nano interfaces on a single substrate, remain challenging. In the present study, the smallest-ever square nanochannels (with a size of 50 nm) were fabricated on fused silica substrates by optimizing the electron beam exposure time, and the absence of channel breaks was confirmed by streaming current measurements. In addition, micro-nano interfaces between 10³ nm nanochannels and 10¹ μm microchannels were fabricated on a single substrate by controlling the hydrophobicity of the nanochannel surfaces. A micro-nano interface for a single cell analysis device, in which a nanochannel was connected to a 10¹ μm single cell chamber, was also fabricated. These new fabrication procedures are expected to advance the basic technologies employed in the field of nanofluidics. Full article

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

► Show Figures

Figure 1

Journal Menu

Journal Browser

Advances in Nanofluidics

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (11 papers)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI