Sakon Rahong - Academia.edu (original) (raw)

Papers by Sakon Rahong

Advanced Materials Research, 2010

Electrode-embedded nanopore is considered as a promising device structure for label-free single-m... more Electrode-embedded nanopore is considered as a promising device structure for label-free single-molecule sequencing, the principle of which is based on nucleotide identification via transverse electron tunnelling current flowing through a DNA translocating through the pore. Yet, fabrication of a molecular-scale electrode-nanopore detector has been a formidable task that requires atomic-level alignment of a few nanometer sized pore and an electrode gap. Here, we report single-molecule detection using a nucleotide-sized sensing electrode embedded in-plane nanopore. We developed a self-alignment technique to form a nanopore-nanoelectrode solid-state device consisting of a sub-nanometer scale electrode gap in a 15 nm-sized SiO 2 pore. We demonstrate single-molecule counting of nucleotide-sized metal-encapsulated fullerenes in a liquid using the electrode-integrated nanopore sensor. We also performed electrical identification of nucleobases in a DNA oligomer, thereby suggesting the potential use of this synthetic electrode-in-nanopore as a platform for electrical DNA sequencing.

Abstract: A microfabricated device is fabricated by depositing a first metal layer on a substrate... more Abstract: A microfabricated device is fabricated by depositing a first metal layer on a substrate to provide a first electrode of an electrostatic actuator, depositing a first structural polymer layer over the first metal layer, depositing a second metal layer over said first structural polymer layer to form a second electrode of the electrostatic actuator, depositing an insulating layer over said first structural polymer layer, planarizing the insulating layer, etching the first structural polymer layer through the insulating layer and the second metal ...

Lab Chip, 2016

This review highlights the most promising applications of nanowires for bioanalytical chemistry a... more This review highlights the most promising applications of nanowires for bioanalytical chemistry and medical diagnostics. The materials discussed here are metal oxide and Si semiconductors, which are integrated with various microfluidic systems. Nanowire structures offer desirable advantages such as a very small diameter size with a high aspect ratio and a high surface-to-volume ratio without grain boundaries; consequently, nanowires are promising tools to study biological systems. This review starts with the integration of nanowire structures into microfluidic systems, followed by the discussion of the advantages of nanowire structures in the separation, manipulation and purification of biomolecules (DNA, RNA and proteins). Next, some representative nanowire devices are introduced for biosensors from molecular to cellular levels based on electrical and optical approaches. Finally, we conclude the review by highlighting some bio-applications for nanowires and presenting the next challenges that must be overcome to improve the capabilities of nanowire structures for biological and medical systems.

This work reports a new approach to synthesize carbon nanostructures by the Chemical Vapor Deposi... more This work reports a new approach to synthesize carbon nanostructures by the Chemical Vapor Deposition (CVD) technique using Polyoxometalates (POMs) as catalysts. POMs are anionic metal-oxygen complex nanoclusters, which can be synthesized by aqueous chemical processes. Hydrogen and acetylene were used as the carrier gas and the carbon precursor, respectively, for the CVD growth at 700°C. Two methods for the

The photocatalytic reaction of polyoxotungstate [BW 12 O 40 ] 5-, [SiW 12 O 40 ] 4-, [PW 12 O 40 ... more The photocatalytic reaction of polyoxotungstate [BW 12 O 40 ] 5-, [SiW 12 O 40 ] 4-, [PW 12 O 40 ] 3-and [AsW 9 O 33 ] 9-led to the generation of hydrogen gas from aqueous sucrose solution under irradiation of UV light. These photoreactions for each polyoxotungstate were investigated for dependence of pH level and it was displayed that hydrogen gas was obtained at low pH (around pH 2-3) without heterogeneous cocatalyst such as platinum or RuO 2 . The colorless solutions changed to blue-colored solution called heteropoly blue. It indicated that one-or two-electron reduced species were produced with accompanying dehydrogenation of sucrose. Especially, the reaction of [SiW 12 O 40 ] 4-and [BW 12 O 40 ] 5-resulted in the generation of hydrogen gas with a higher yield than others. UV spectra of [SiW 12 O 40 ] 4-and [BW 12 O 40 ] 5-aqueous solution in the presence of sucrose exhibited two absorption peaks around 490 and 730, and 495 and 695 nm, respectively. The intensity increased with e...

Metal thin films are interesting for use in a wide variety of applications, including electrodes ... more Metal thin films are interesting for use in a wide variety of applications, including electrodes in the devices, resistance temperature detector and resistive heater. The thermal treatments have been found to improve surface morphology of metal film. In this work, we investigate the effect of annealing condition of the platinum thin films. The Pt/Cr thin film with a thickness of 200/20 nm was deposited on a dielectric film by electron beam evaporation onto 6 inch silicon-substrate. The deposition rate was kept at 0.01 nm/s and the substrate temperature was maintained at 100 °C during evaporation process. Evaporated-Pt film was annealed in a quartz tube furnace for 120 minute at difference temperature. The surface morphologies of prepared Pt films were observed by field emission scanning electron microscope (FE-SEM) and Atomic Force Microscope (AFM). After annealing, the grain size of the Pt film increased and the electrical resistivity decreased remarkably. The morphologies of the Pt film revealed from FE-SEM and AFM show the reasons why the over annealing temperature affect the increasing of resistivity. A study of effect of annealing temperature of the Pt film will be utilized for microheater and temperature sensor applications.

A new polyaniline/cabon nanotube/platinum (PANI/CNT/Pt) hybrid material has successfully been syn... more A new polyaniline/cabon nanotube/platinum (PANI/CNT/Pt) hybrid material has successfully been synthesized by using electrochemical techniques. PANI/CNT film was fabricated on tin oxide (SnO 2) glass electrode by electropolymerization of aniline under continuous potential. In addition, Pt particles were deposited on PANI thin film by electrochemical deposition. Pt on PANI film led to the formation of nano particles under continuous potential for deposition durations 200s. Pt particles and morphology of hybrid thin films were characterized by scanning electron microscope (SEM). Additionally, the size of Pt particles deposited into PANI/CNT film was smaller than those directly deposited on PANI film without CNT. The capacitance values of these materials were studied by LCR meter frequency in order 1 -100 kHz. It was found that the specific capacitance of PANI/CNT/Pt hybrid film reached up to 22 µF at frequency 1 kHz and the capacitance results were shown higher than pure PANI and PANI/...

Laser interference method is successfully used as the efficient tool for photonic crystal templat... more Laser interference method is successfully used as the efficient tool for photonic crystal template patterning. This technique can produce a sub-wavelength grating within a large area. The interference angles are chosen at 10 and 15 degrees in order to produce 850 and 1300 nm of grating period. The surface morphology of fabricated templates was characterized using Field-Emission Scanning Electron Microscope (FE-SEM) and Atomic Force Microscope (AFM). This template is used as a master mold for polydimethylsiloxane (PDMS) duplication. The photonic crystals device is obtained by evaporation of TiO 2 thin film on PDMS-grating which have advantages for optical biosensor applications. Background Currently, photonic crystal label-free optical biosensors have been demonstrated as a high resolution device for a diversity of cell assays and biochemical detection [1, 2]. The device comprises of a sub-wavelength grating and a waveguide which can be embedded within a same layer[3]. Due to its gui...

Scientific Reports, 2015

Separation and analysis of biomolecules represent crucial processes for biological and biomedical... more Separation and analysis of biomolecules represent crucial processes for biological and biomedical engineering development; however, separation resolution and speed for biomolecules analysis still require improvements. To achieve separation and analysis of biomolecules in a short time, the use of highly-ordered nanostructures fabricated by top-down or bottom-up approaches have been proposed. Here, we reported on the use of three-dimensional (3D) nanowire structures embedded in microchannels fabricated by a bottom-up approach for ultrafast separation of small biomolecules, such as DNA, protein, and RNA molecules. The 3D nanowire structures could analyze a mixture of DNA molecules (50-1000 bp) within 50 s, a mixture of protein molecules (20-340 kDa) within 5 s, and a mixture of RNA molecules (100-1000 bases) within 25 s. And, we could observe the electrophoretic mobility difference of biomolecules as a function of molecular size in the 3D nanowire structures. Since the present methodology allows users to control the pore size of sieving materials by varying the number of cycles for nanowire growth, the 3D nanowire structures have a good potential for use as alternatives for other sieving materials.

Israel Journal of Chemistry, 2014

ABSTRACT Nanostructures based on nanotechnologies have opened up a novel research field for the f... more ABSTRACT Nanostructures based on nanotechnologies have opened up a novel research field for the fast analysis of biomolecules with ultrahigh resolution, including the analysis of single biomolecules. Nanostructures for electrophoretic separation, especially, are an exciting topic among researchers in many areas, and their designs are widely expected to contribute to the goal of developing a single separation tool for a wide range of biomolecules. In this review, nanopillar, nanowall, and nanowire devices are introduced for fast separation of DNA molecules and protein samples, and the numerous advantages of these devices are described. This review also outlines the fabrication processes for nanostructures, including “top-down” and “bottom-up” nanofabrication approaches. Besides describing the fast separation of biomolecules, the electroosmotic flow (EOF) suppression effect, and its related online concentration technique in nanopillar devices, is reviewed. The nanowall devices have the unique feature that longer DNA molecules migrate faster than shorter ones, and that is completely different from the separation behavior of DNA molecules based on nanopillar devices. The feasibility is shown for self-assembly of the nanowire structure embedded in a microchannel on a fused silica substrate, as a means to separate DNA molecules. Applications of a newly-fabricated 3D network structure with spatial density control for the fast separation of a wide range of DNA molecules are also given.

Analytical sciences : the international journal of the Japan Society for Analytical Chemistry, 2015

Molecular filtration and purification play important roles for biomolecule analysis. However, it ... more Molecular filtration and purification play important roles for biomolecule analysis. However, it is still necessary to improve efficiency and reduce the filtration time. Here, we show self-assembled nanowire arrays as three-dimensional (3D) nanopores embedded in a microfluidic channel for ultrafast DNA filtration. The 3D nanopore structure was formed by a vapor-liquid-solid (VLS) nanowire growth technique, which allowed us to control pore size of the filtration material by varying the number of growth cycles. λ DNA molecules (48.5 kbp) were filtrated from a mixture of T4 DNA (166 kbp) at the entrance of the 3D nanopore structure within 1 s under an applied electric field. Moreover, we observed single DNA molecule migration of T4 and λ DNA molecules to clarify the filtration mechanism. The 3D nanopore structure has simplicity of fabrication, flexibility of pore size control and reusability for biomolecule filtration. Consequently it is an excellent material for biomolecular filtration.

Scientific reports, 2014

On the development of flexible electronics, a highly flexible nonvolatile memory, which is an imp... more On the development of flexible electronics, a highly flexible nonvolatile memory, which is an important circuit component for the portability, is necessary. However, the flexibility of existing nonvolatile memory has been limited, e.g. the smallest radius into which can be bent has been millimeters range, due to the difficulty in maintaining memory properties while bending. Here we propose the ultra flexible resistive nonvolatile memory using Ag-decorated cellulose nanofiber paper (CNP). The Ag-decorated CNP devices showed the stable nonvolatile memory effects with 6 orders of ON/OFF resistance ratio and the small standard deviation of switching voltage distribution. The memory performance of CNP devices can be maintained without any degradation when being bent down to the radius of 350 μm, which is the smallest value compared to those of existing any flexible nonvolatile memories. Thus the present device using abundant and mechanically flexible CNP offers a highly flexible nonvolat...

Scientific reports, Jan 4, 2014

Controlling the post-growth assembly of nanowires is an important challenge in the development of... more Controlling the post-growth assembly of nanowires is an important challenge in the development of functional bottom-up devices. Although various methods have been developed for the controlled assembly of nanowires, it is still a challenging issue to align selectively heterogeneous nanowires at desired spatial positions on the substrate. Here we report a size selective deposition and sequential alignment of nanowires by utilizing micrometer scale hydrophilic/hydrophobic patterned substrate. Nanowires dispersed within oil were preferentially deposited only at a water/oil interface onto the hydrophilic patterns. The diameter size of deposited nanowires was strongly limited by the width of hydrophilic patterns, exhibiting the nanoscale size selectivity of nanowires deposited onto micrometer scale hydrophilic patterns. Such size selectivity was due to the nanoscale height variation of a water layer formed onto the micrometer scale hydrophilic patterns. We successfully demonstrated the se...

Scientific Reports, 2014

Analyzing sizes of DNA via electrophoresis using a gel has played an important role in the recent... more Analyzing sizes of DNA via electrophoresis using a gel has played an important role in the recent, rapid progress of biology and biotechnology. Although analyzing DNA over a wide range of sizes in a short time is desired, no existing electrophoresis methods have been able to fully satisfy these two requirements. Here we propose a novel method using a rigid 3D network structure composed of solid nanowires within a microchannel. This rigid network structure enables analysis of DNA under applied DC electric fields for a large DNA size range (100 bp-166 kbp) within 13 s, which are much wider and faster conditions than those of any existing methods. The network density is readily varied for the targeted DNA size range by tailoring the number of cycles of the nanowire growth only at the desired spatial position within the microchannel. The rigid dense 3D network structure with spatial density control plays an important role in determining the capability for analyzing DNA. Since the present method allows the spatial location and density of the nanostructure within the microchannels to be defined, this unique controllability offers a new strategy to develop an analytical method not only for DNA but also for other biological molecules. S ince researchers have revealed the critical role played by information stored within DNA molecules in the complex biological activities occurring in living systems 1-3 , various methodologies have been developed to analyze DNA molecules 4,5 . Among them, gel electrophoresis is the most prominent and commercially available standard method to analyze the size of DNA molecules due to the great controllability of pore sizes and also the inexpensiveness of electrophoresis devices 6 . On the other hand, the limitations of gel electrophoresis have also been pointed out, and they are the difficulty in analyzing relatively long DNA molecules in a short time, the high skill required for appropriately preparing the gel, and the requirement of gel concentration control for each targeted DNA size 7-9 . Recently, data for a wide range of DNA size have been obtained using the hydrodynamic chromatography method 10 . Although the analysis time using this method is faster than that using gel electrophoresis, it still takes several tens of minutes for the fastest analysis. To realize an analysis on the time scale of seconds, nanostructure electrophoresis has attracted much attention as a novel method to overcome the above issues with gel electrophoresis 11 .

RSC Advances, 2012

Creating sublithographic scale uniform nanowires for large area is an important issue for nanowir... more Creating sublithographic scale uniform nanowires for large area is an important issue for nanowirebased various device applications. Although anodic aluminium oxide (AAO) membrane is a promising technique, existing attached AAO membrane mask methods have not been able to fabricate such small nanowires for large areas due to difficulties on transferring a thin membrane.

Advanced Materials Research, 2010

Scientific Reports, 2011

Electrode-embedded nanopore is considered as a promising device structure for label-free single-m... more Electrode-embedded nanopore is considered as a promising device structure for label-free single-molecule sequencing, the principle of which is based on nucleotide identification via transverse electron tunnelling current flowing through a DNA translocating through the pore. Yet, fabrication of a molecular-scale electrode-nanopore detector has been a formidable task that requires atomic-level alignment of a few nanometer sized pore and an electrode gap. Here, we report single-molecule detection using a nucleotide-sized sensing electrode embedded in-plane nanopore. We developed a self-alignment technique to form a nanopore-nanoelectrode solid-state device consisting of a sub-nanometer scale electrode gap in a 15 nm-sized SiO 2 pore. We demonstrate single-molecule counting of nucleotide-sized metal-encapsulated fullerenes in a liquid using the electrode-integrated nanopore sensor. We also performed electrical identification of nucleobases in a DNA oligomer, thereby suggesting the potential use of this synthetic electrode-in-nanopore as a platform for electrical DNA sequencing.

Novel optoelectronic materials based on II-VI inorganic/organic low-dimensional heterostructure w... more Novel optoelectronic materials based on II-VI inorganic/organic low-dimensional heterostructure were successfully grown by electron beam evaporator. The structures were based on ZnSe, tris(8- hydroxyquinoline) aluminum (Alq 3 ) and N,N'-bis(3-methylphenyl)-N,N'-diphenyl-benzidine (TPD). The surface morphology of the structures was investigated by atomic force microscopy and field emission scanning electron microscope. The optical and electronic properties were examined by photoluminescence, photocurrent and

Advanced Materials Research, 2010

Electrode-embedded nanopore is considered as a promising device structure for label-free single-m... more Electrode-embedded nanopore is considered as a promising device structure for label-free single-molecule sequencing, the principle of which is based on nucleotide identification via transverse electron tunnelling current flowing through a DNA translocating through the pore. Yet, fabrication of a molecular-scale electrode-nanopore detector has been a formidable task that requires atomic-level alignment of a few nanometer sized pore and an electrode gap. Here, we report single-molecule detection using a nucleotide-sized sensing electrode embedded in-plane nanopore. We developed a self-alignment technique to form a nanopore-nanoelectrode solid-state device consisting of a sub-nanometer scale electrode gap in a 15 nm-sized SiO 2 pore. We demonstrate single-molecule counting of nucleotide-sized metal-encapsulated fullerenes in a liquid using the electrode-integrated nanopore sensor. We also performed electrical identification of nucleobases in a DNA oligomer, thereby suggesting the potential use of this synthetic electrode-in-nanopore as a platform for electrical DNA sequencing.

Abstract: A microfabricated device is fabricated by depositing a first metal layer on a substrate... more Abstract: A microfabricated device is fabricated by depositing a first metal layer on a substrate to provide a first electrode of an electrostatic actuator, depositing a first structural polymer layer over the first metal layer, depositing a second metal layer over said first structural polymer layer to form a second electrode of the electrostatic actuator, depositing an insulating layer over said first structural polymer layer, planarizing the insulating layer, etching the first structural polymer layer through the insulating layer and the second metal ...

Lab Chip, 2016

This review highlights the most promising applications of nanowires for bioanalytical chemistry a... more This review highlights the most promising applications of nanowires for bioanalytical chemistry and medical diagnostics. The materials discussed here are metal oxide and Si semiconductors, which are integrated with various microfluidic systems. Nanowire structures offer desirable advantages such as a very small diameter size with a high aspect ratio and a high surface-to-volume ratio without grain boundaries; consequently, nanowires are promising tools to study biological systems. This review starts with the integration of nanowire structures into microfluidic systems, followed by the discussion of the advantages of nanowire structures in the separation, manipulation and purification of biomolecules (DNA, RNA and proteins). Next, some representative nanowire devices are introduced for biosensors from molecular to cellular levels based on electrical and optical approaches. Finally, we conclude the review by highlighting some bio-applications for nanowires and presenting the next challenges that must be overcome to improve the capabilities of nanowire structures for biological and medical systems.

This work reports a new approach to synthesize carbon nanostructures by the Chemical Vapor Deposi... more This work reports a new approach to synthesize carbon nanostructures by the Chemical Vapor Deposition (CVD) technique using Polyoxometalates (POMs) as catalysts. POMs are anionic metal-oxygen complex nanoclusters, which can be synthesized by aqueous chemical processes. Hydrogen and acetylene were used as the carrier gas and the carbon precursor, respectively, for the CVD growth at 700°C. Two methods for the

The photocatalytic reaction of polyoxotungstate [BW 12 O 40 ] 5-, [SiW 12 O 40 ] 4-, [PW 12 O 40 ... more The photocatalytic reaction of polyoxotungstate [BW 12 O 40 ] 5-, [SiW 12 O 40 ] 4-, [PW 12 O 40 ] 3-and [AsW 9 O 33 ] 9-led to the generation of hydrogen gas from aqueous sucrose solution under irradiation of UV light. These photoreactions for each polyoxotungstate were investigated for dependence of pH level and it was displayed that hydrogen gas was obtained at low pH (around pH 2-3) without heterogeneous cocatalyst such as platinum or RuO 2 . The colorless solutions changed to blue-colored solution called heteropoly blue. It indicated that one-or two-electron reduced species were produced with accompanying dehydrogenation of sucrose. Especially, the reaction of [SiW 12 O 40 ] 4-and [BW 12 O 40 ] 5-resulted in the generation of hydrogen gas with a higher yield than others. UV spectra of [SiW 12 O 40 ] 4-and [BW 12 O 40 ] 5-aqueous solution in the presence of sucrose exhibited two absorption peaks around 490 and 730, and 495 and 695 nm, respectively. The intensity increased with e...

Metal thin films are interesting for use in a wide variety of applications, including electrodes ... more Metal thin films are interesting for use in a wide variety of applications, including electrodes in the devices, resistance temperature detector and resistive heater. The thermal treatments have been found to improve surface morphology of metal film. In this work, we investigate the effect of annealing condition of the platinum thin films. The Pt/Cr thin film with a thickness of 200/20 nm was deposited on a dielectric film by electron beam evaporation onto 6 inch silicon-substrate. The deposition rate was kept at 0.01 nm/s and the substrate temperature was maintained at 100 °C during evaporation process. Evaporated-Pt film was annealed in a quartz tube furnace for 120 minute at difference temperature. The surface morphologies of prepared Pt films were observed by field emission scanning electron microscope (FE-SEM) and Atomic Force Microscope (AFM). After annealing, the grain size of the Pt film increased and the electrical resistivity decreased remarkably. The morphologies of the Pt film revealed from FE-SEM and AFM show the reasons why the over annealing temperature affect the increasing of resistivity. A study of effect of annealing temperature of the Pt film will be utilized for microheater and temperature sensor applications.

A new polyaniline/cabon nanotube/platinum (PANI/CNT/Pt) hybrid material has successfully been syn... more A new polyaniline/cabon nanotube/platinum (PANI/CNT/Pt) hybrid material has successfully been synthesized by using electrochemical techniques. PANI/CNT film was fabricated on tin oxide (SnO 2) glass electrode by electropolymerization of aniline under continuous potential. In addition, Pt particles were deposited on PANI thin film by electrochemical deposition. Pt on PANI film led to the formation of nano particles under continuous potential for deposition durations 200s. Pt particles and morphology of hybrid thin films were characterized by scanning electron microscope (SEM). Additionally, the size of Pt particles deposited into PANI/CNT film was smaller than those directly deposited on PANI film without CNT. The capacitance values of these materials were studied by LCR meter frequency in order 1 -100 kHz. It was found that the specific capacitance of PANI/CNT/Pt hybrid film reached up to 22 µF at frequency 1 kHz and the capacitance results were shown higher than pure PANI and PANI/...

Laser interference method is successfully used as the efficient tool for photonic crystal templat... more Laser interference method is successfully used as the efficient tool for photonic crystal template patterning. This technique can produce a sub-wavelength grating within a large area. The interference angles are chosen at 10 and 15 degrees in order to produce 850 and 1300 nm of grating period. The surface morphology of fabricated templates was characterized using Field-Emission Scanning Electron Microscope (FE-SEM) and Atomic Force Microscope (AFM). This template is used as a master mold for polydimethylsiloxane (PDMS) duplication. The photonic crystals device is obtained by evaporation of TiO 2 thin film on PDMS-grating which have advantages for optical biosensor applications. Background Currently, photonic crystal label-free optical biosensors have been demonstrated as a high resolution device for a diversity of cell assays and biochemical detection [1, 2]. The device comprises of a sub-wavelength grating and a waveguide which can be embedded within a same layer[3]. Due to its gui...

Scientific Reports, 2015

Separation and analysis of biomolecules represent crucial processes for biological and biomedical... more Separation and analysis of biomolecules represent crucial processes for biological and biomedical engineering development; however, separation resolution and speed for biomolecules analysis still require improvements. To achieve separation and analysis of biomolecules in a short time, the use of highly-ordered nanostructures fabricated by top-down or bottom-up approaches have been proposed. Here, we reported on the use of three-dimensional (3D) nanowire structures embedded in microchannels fabricated by a bottom-up approach for ultrafast separation of small biomolecules, such as DNA, protein, and RNA molecules. The 3D nanowire structures could analyze a mixture of DNA molecules (50-1000 bp) within 50 s, a mixture of protein molecules (20-340 kDa) within 5 s, and a mixture of RNA molecules (100-1000 bases) within 25 s. And, we could observe the electrophoretic mobility difference of biomolecules as a function of molecular size in the 3D nanowire structures. Since the present methodology allows users to control the pore size of sieving materials by varying the number of cycles for nanowire growth, the 3D nanowire structures have a good potential for use as alternatives for other sieving materials.

Israel Journal of Chemistry, 2014

ABSTRACT Nanostructures based on nanotechnologies have opened up a novel research field for the f... more ABSTRACT Nanostructures based on nanotechnologies have opened up a novel research field for the fast analysis of biomolecules with ultrahigh resolution, including the analysis of single biomolecules. Nanostructures for electrophoretic separation, especially, are an exciting topic among researchers in many areas, and their designs are widely expected to contribute to the goal of developing a single separation tool for a wide range of biomolecules. In this review, nanopillar, nanowall, and nanowire devices are introduced for fast separation of DNA molecules and protein samples, and the numerous advantages of these devices are described. This review also outlines the fabrication processes for nanostructures, including “top-down” and “bottom-up” nanofabrication approaches. Besides describing the fast separation of biomolecules, the electroosmotic flow (EOF) suppression effect, and its related online concentration technique in nanopillar devices, is reviewed. The nanowall devices have the unique feature that longer DNA molecules migrate faster than shorter ones, and that is completely different from the separation behavior of DNA molecules based on nanopillar devices. The feasibility is shown for self-assembly of the nanowire structure embedded in a microchannel on a fused silica substrate, as a means to separate DNA molecules. Applications of a newly-fabricated 3D network structure with spatial density control for the fast separation of a wide range of DNA molecules are also given.

Analytical sciences : the international journal of the Japan Society for Analytical Chemistry, 2015

Molecular filtration and purification play important roles for biomolecule analysis. However, it ... more Molecular filtration and purification play important roles for biomolecule analysis. However, it is still necessary to improve efficiency and reduce the filtration time. Here, we show self-assembled nanowire arrays as three-dimensional (3D) nanopores embedded in a microfluidic channel for ultrafast DNA filtration. The 3D nanopore structure was formed by a vapor-liquid-solid (VLS) nanowire growth technique, which allowed us to control pore size of the filtration material by varying the number of growth cycles. λ DNA molecules (48.5 kbp) were filtrated from a mixture of T4 DNA (166 kbp) at the entrance of the 3D nanopore structure within 1 s under an applied electric field. Moreover, we observed single DNA molecule migration of T4 and λ DNA molecules to clarify the filtration mechanism. The 3D nanopore structure has simplicity of fabrication, flexibility of pore size control and reusability for biomolecule filtration. Consequently it is an excellent material for biomolecular filtration.

Scientific reports, 2014

On the development of flexible electronics, a highly flexible nonvolatile memory, which is an imp... more On the development of flexible electronics, a highly flexible nonvolatile memory, which is an important circuit component for the portability, is necessary. However, the flexibility of existing nonvolatile memory has been limited, e.g. the smallest radius into which can be bent has been millimeters range, due to the difficulty in maintaining memory properties while bending. Here we propose the ultra flexible resistive nonvolatile memory using Ag-decorated cellulose nanofiber paper (CNP). The Ag-decorated CNP devices showed the stable nonvolatile memory effects with 6 orders of ON/OFF resistance ratio and the small standard deviation of switching voltage distribution. The memory performance of CNP devices can be maintained without any degradation when being bent down to the radius of 350 μm, which is the smallest value compared to those of existing any flexible nonvolatile memories. Thus the present device using abundant and mechanically flexible CNP offers a highly flexible nonvolat...

Scientific reports, Jan 4, 2014

Controlling the post-growth assembly of nanowires is an important challenge in the development of... more Controlling the post-growth assembly of nanowires is an important challenge in the development of functional bottom-up devices. Although various methods have been developed for the controlled assembly of nanowires, it is still a challenging issue to align selectively heterogeneous nanowires at desired spatial positions on the substrate. Here we report a size selective deposition and sequential alignment of nanowires by utilizing micrometer scale hydrophilic/hydrophobic patterned substrate. Nanowires dispersed within oil were preferentially deposited only at a water/oil interface onto the hydrophilic patterns. The diameter size of deposited nanowires was strongly limited by the width of hydrophilic patterns, exhibiting the nanoscale size selectivity of nanowires deposited onto micrometer scale hydrophilic patterns. Such size selectivity was due to the nanoscale height variation of a water layer formed onto the micrometer scale hydrophilic patterns. We successfully demonstrated the se...

Scientific Reports, 2014

Analyzing sizes of DNA via electrophoresis using a gel has played an important role in the recent... more Analyzing sizes of DNA via electrophoresis using a gel has played an important role in the recent, rapid progress of biology and biotechnology. Although analyzing DNA over a wide range of sizes in a short time is desired, no existing electrophoresis methods have been able to fully satisfy these two requirements. Here we propose a novel method using a rigid 3D network structure composed of solid nanowires within a microchannel. This rigid network structure enables analysis of DNA under applied DC electric fields for a large DNA size range (100 bp-166 kbp) within 13 s, which are much wider and faster conditions than those of any existing methods. The network density is readily varied for the targeted DNA size range by tailoring the number of cycles of the nanowire growth only at the desired spatial position within the microchannel. The rigid dense 3D network structure with spatial density control plays an important role in determining the capability for analyzing DNA. Since the present method allows the spatial location and density of the nanostructure within the microchannels to be defined, this unique controllability offers a new strategy to develop an analytical method not only for DNA but also for other biological molecules. S ince researchers have revealed the critical role played by information stored within DNA molecules in the complex biological activities occurring in living systems 1-3 , various methodologies have been developed to analyze DNA molecules 4,5 . Among them, gel electrophoresis is the most prominent and commercially available standard method to analyze the size of DNA molecules due to the great controllability of pore sizes and also the inexpensiveness of electrophoresis devices 6 . On the other hand, the limitations of gel electrophoresis have also been pointed out, and they are the difficulty in analyzing relatively long DNA molecules in a short time, the high skill required for appropriately preparing the gel, and the requirement of gel concentration control for each targeted DNA size 7-9 . Recently, data for a wide range of DNA size have been obtained using the hydrodynamic chromatography method 10 . Although the analysis time using this method is faster than that using gel electrophoresis, it still takes several tens of minutes for the fastest analysis. To realize an analysis on the time scale of seconds, nanostructure electrophoresis has attracted much attention as a novel method to overcome the above issues with gel electrophoresis 11 .

RSC Advances, 2012

Creating sublithographic scale uniform nanowires for large area is an important issue for nanowir... more Creating sublithographic scale uniform nanowires for large area is an important issue for nanowirebased various device applications. Although anodic aluminium oxide (AAO) membrane is a promising technique, existing attached AAO membrane mask methods have not been able to fabricate such small nanowires for large areas due to difficulties on transferring a thin membrane.

Advanced Materials Research, 2010

Scientific Reports, 2011

Electrode-embedded nanopore is considered as a promising device structure for label-free single-m... more Electrode-embedded nanopore is considered as a promising device structure for label-free single-molecule sequencing, the principle of which is based on nucleotide identification via transverse electron tunnelling current flowing through a DNA translocating through the pore. Yet, fabrication of a molecular-scale electrode-nanopore detector has been a formidable task that requires atomic-level alignment of a few nanometer sized pore and an electrode gap. Here, we report single-molecule detection using a nucleotide-sized sensing electrode embedded in-plane nanopore. We developed a self-alignment technique to form a nanopore-nanoelectrode solid-state device consisting of a sub-nanometer scale electrode gap in a 15 nm-sized SiO 2 pore. We demonstrate single-molecule counting of nucleotide-sized metal-encapsulated fullerenes in a liquid using the electrode-integrated nanopore sensor. We also performed electrical identification of nucleobases in a DNA oligomer, thereby suggesting the potential use of this synthetic electrode-in-nanopore as a platform for electrical DNA sequencing.

Novel optoelectronic materials based on II-VI inorganic/organic low-dimensional heterostructure w... more Novel optoelectronic materials based on II-VI inorganic/organic low-dimensional heterostructure were successfully grown by electron beam evaporator. The structures were based on ZnSe, tris(8- hydroxyquinoline) aluminum (Alq 3 ) and N,N'-bis(3-methylphenyl)-N,N'-diphenyl-benzidine (TPD). The surface morphology of the structures was investigated by atomic force microscopy and field emission scanning electron microscope. The optical and electronic properties were examined by photoluminescence, photocurrent and