Linker-free directed assembly of high-performance integrated devices based on nanotubes and nanowires

Highly Sensitive Real-Time Monitoring of Adenosine Receptor Activities in Nonsmall Cell Lung Cancer Cells Using Carbon Nanotube Field-Effect Transistors

Adenosine metabolism through adenosine receptors plays a critical role in lung cancer biology. Although recent studies showed the potential of targeting adenosine receptors as drug targets for lung cancer treatment, conventional methods for investigating receptor activities often suffer from various drawbacks, including low sensitivity and slow analysis speed. In this study, adenosine receptor activities in nonsmall cell lung cancer (NSCLC) cells were monitored in real time with high sensitivity through a carbon nanotube field-effect transistor (CNT-FET). In this method, we hybridized a CNT-FET with NSCLC cells expressing A2A and A2B adenosine receptors to construct a hybrid platform. This platform could detect adenosine, an endogenous ligand of adenosine receptors, down to 1 fM in real time and sensitively discriminate adenosine among other nucleosides. Furthermore, we could also utilize the platform to detect adenosine in complicated environments, such as human serum. Notably, our hybrid platform allowed us to monitor pharmacological effects between adenosine and other drugs, including dipyridamole and theophylline, even in human serum samples. These results indicate that the NSCLC cell-hybridized CNT-FET can be a practical tool for biomedical applications, such as the evaluation and screening of drug-candidate substances.

Bioelectronic Tongues Mimicking Insect Taste Systems for Real-Time Discrimination between Natural and Artificial Sweeteners

A bioelectronic tongue (B-ET) mimicking insect taste systems is developed for the real-time detection and discrimination of natural and artificial sweeteners. Here, a carbon nanotube field-effect transistor (CNT-FET) was hybridized with nanovesicles including the honeybee sugar taste receptor, gustatory receptor 1 of Apis mellifera (AmGr1). This strategy allowed us to detect glucose, a major component of nectar, down to 100 fM in real time and identify sweet tastants from other tastants. It could also be utilized for the detection of glucose in dextrose tablet solutions. Importantly, we demonstrated the discrimination between natural and artificial sweeteners down to 10 pM even in real beverages such as decaffeinated coffee using our hybrid platform. In this respect, our B-ET mimicking insect taste systems can be a powerful tool for various applications such as food screening and basic studies on insect taste systems.

Evaluation of site-selective drug effects on GABA receptors using nanovesicle-carbon nanotube hybrid devices

Site-selective drug effects on the ion-channel activities of γ-aminobutyric acid type A (GABA_A) receptors are evaluated by using a nanovesicle-carbon nanotube hybrid device. Here, nanovesicles containing GABA_A receptors are immobilized on the channel region of a carbon nanotube field-effect transistor. The receptor responses of this hybrid device to GABA are detected with a high sensitivity down to ∼1 aM even in the presence of other neurotransmitters. Further, sensitivity differences between two GABA_A-receptor-subunit compositions of α5β2γ2 and α1β2γ2 are assessed by normalizing the dose-dependent responses obtained from these hybrid devices. Specifically, the GABA concentration that produces 50% of maximal response (EC₅₀) is obtained as ∼10 pM for α5β2γ2 subunits and ∼1 nM for α1β2γ2 subunits of GABA_A receptor. Significantly, the potency profiles of both antagonist and agonist of GABA_A receptor can be evaluated by analyzing EC₅₀ values in the presence and absence of those drugs. A competitive antagonist increases the EC₅₀ value of GABA by binding to the same site as GABA, while an allosteric agonist reduces it by binding to a different site. These results indicate that this hybrid device can be a powerful tool for the evaluation of candidate drug substances modulating GABA-mediated neurotransmission.

Magnetic Manipulation of Nanowires for Engineered Stretchable Electronics

Nanowires are often key ingredients of high-tech composite materials. The properties and performance of devices created using these, depend heavily on the structure and density of the embedded nanowires. Despite significant efforts, a process that can be adapted to different materials, compatible with current nanowire deposition methods, and that is able to control both variables simultaneously has not been achieved yet. In this work, we show that we can use low magnetic fields (80 mT) to manipulate nanowires by electrostatically coating them with superparamagnetic iron oxide nanoparticles in an aqueous solution. Monolayers, multilayers, and hierarchical structures of oriented nanowires were achieved in a highly ordered manner using vacuum filtration for two types of nanowires: silver and gold-coated titanium dioxide nanowires. The produced films were embedded in an elastomer, and the strain-dependent electrical properties of the resulting composites were investigated. The orientation of the assembly with respect to the tensile strain heavily impacts the performance of the composites. Composites containing nanowires perpendicular to the strain direction exhibit an extremely low gauge factor. On the other hand, when nanowires are arranged parallel to the strain direction, the composites have a high gauge factor. The possibility to orient nanowires during the processing steps is not only interesting for the shown strain sensing application but also expected to be useful in many other areas of material science.

Cysteine-induced one-pot synthesis of Au nanoparticle chains with tuneable NIR absorption and application in photothermal-chemo cancer therapy

facile L-cysteine (L-cys) mediated one-pot green method is explored to prepare chain-like Au nanoparticles (AuNPs) assembly structure. In such method, the L-cys can be used as a morphology inducer to...

Dense Assembly of Finely Patterned Semiconducting Single-Walled Carbon Nanotubes via a Selective Transfer Method of Nanotube-Attracting Layers

Development of technology for assembled single-walled carbon nanotube (SWCNT) film with the fine resolution is an essential technique for penetrating practical electronic applications. A promising approach is the assembly method by adding a chemical-functionalizing substrate to enhance affinity between the SWCNTs and the substrate. However, the various introduced approaches for solution-based assembly have suffered from low SWCNT deposition selectivity or low SWCNT deposition density. Herein, we demonstrated a facile method for selectively assembling semiconducting SWCNT network on the substrate. The substrate was prepared via a transfer printing of a poly-l-lysine (PLL)-coated poly(dimethylsiloxane) (PDMS) stamp. The thermal-assisted transfer method enabled an ultrafine PLL pattern (≤4 μm) and a high transfer yield (96.5%) by only one-time stamping without a change of the SWCNT-attracting nature. So, semiconducting SWCNTs were deposited on the patterned regions selectively and precisely. The benefit of the patterned semiconducting SWCNTs was lowering leakage current and turn-on voltage in the transfer characteristics by suppressing attachment of unnecessary SWCNT network. They showed excellent electrical performance, a log₁₀(I_on/I_off) ratio of 4.76, and an average value of linear field-effect mobility of 7.56 cm²/(V s). This research provides a simple but high-quality assembling technique of semiconducting SWCNTs, thereby improving the feasibility of solution-processed SWCNT-TFTs.

Bioelectronic Skin Based on Nociceptive Ion Channel for Human-Like Perception of Cold Pains

A bioelectronic skin device based on nociceptive ion channels in nanovesicles is developed for the detection of chemical cold-pain stimuli and cold environments just like human somesthetic sensory systems. The human transient receptor potential ankyrin 1 (hTRPA1) is involved in transmission and modulation of cold-pain sensations. In the bioelectronic skin, the nanovesicles containing the hTRPA1 nociceptive ion channel protein reacts to cold-pain stimuli, and it is electrically monitored through carbon nanotube transistor devices based on floating electrodes. The bioelectronic skin devices sensitively detect chemical cold-pain stimuli like cinnamaldehyde at 10 fm, and selectively discriminate cinnamaldehyde among other chemical stimuli. Further, the bioelectronic skin is used to evaluate the effect of cold environments on the response of the hTRPA1, finding that the nociceptive ion channel responds more sensitively to cinnamaldehyde at lower temperatures than at higher temperatures. The bioelectronic skin device could be useful for a basic study on somesthetic systems such as cold-pain sensation, and should be used for versatile applications such as screening of foods and drugs.

Planar Growth, Integration, and Applications of Semiconducting Nanowires

Silicon and other inorganic semiconductor nanowires (NWs) have been extensively investigated in the last two decades for constructing high-performance nanoelectronics, sensors, and optoelectronics. For many of these applications, these tiny building blocks have to be integrated into the existing planar electronic platform, where precise location, orientation, and layout controls are indispensable. In the advent of More-than-Moore's era, there are also emerging demands for a programmable growth engineering of the geometry, composition, and line-shape of NWs on planar or out-of-plane 3D sidewall surfaces. Here, the critical technologies established for synthesis, transferring, and assembly of NWs upon planar surface are examined; then, the recent progress of in-plane growth of horizontal NWs directly upon crystalline or patterned substrates, constrained by using nanochannels, an epitaxial interface, or amorphous thin film precursors is discussed. Finally, the unique capabilities of planar growth of NWs in achieving precise guided growth control, programmable geometry, composition, and line-shape engineering are reviewed, followed by their latest device applications in building high-performance field-effect transistors, photodetectors, stretchable electronics, and 3D stacked-channel integration.

Ion-Selective Carbon Nanotube Field-Effect Transistors for Monitoring Drug Effects on Nicotinic Acetylcholine Receptor Activation in Live Cells

We developed ion-selective field-effect transistor (FET) sensors with floating electrodes for the monitoring of the potassium ion release by the stimulation of nicotinic acetylcholine receptors (nAChRs) on PC12 cells. Here, ion-selective valinomycin-polyvinyl chloride (PVC) membranes were coated on the floating electrode-based carbon nanotube (CNT) FETs to build the sensors. The sensors could selectively measure potassium ions with a minimum detection limit of 1 nM. We utilized the sensor for the real-time monitoring of the potassium ion released from a live cell stimulated by nicotine. Notably, this method also allowed us to quantitatively monitor the cell responses by agonists and antagonists of nAChRs. These results suggest that our ion-selective CNT-FET sensor has potential uses in biological and medical researches such as the monitoring of ion-channel activity and the screening of drugs.

Nanoscale Patterning of Carbon Nanotubes: Techniques, Applications, and Future

Carbon nanotube (CNT) devices and electronics are achieving maturity and directly competing or surpassing devices that use conventional materials. CNTs have demonstrated ballistic conduction, minimal scaling effects, high current capacity, low power requirements, and excellent optical/photonic properties; making them the ideal candidate for a new material to replace conventional materials in next-generation electronic and photonic systems. CNTs also demonstrate high stability and flexibility, allowing them to be used in flexible, printable, and/or biocompatible electronics. However, a major challenge to fully commercialize these devices is the scalable placement of CNTs into desired micro/nanopatterns and architectures to translate the superior properties of CNTs into macroscale devices. Precise and high throughput patterning becomes increasingly difficult at nanoscale resolution, but it is essential to fully realize the benefits of CNTs. The relatively long, high aspect ratio structures of CNTs must be preserved to maintain their functionalities, consequently making them more difficult to pattern than conventional materials like metals and polymers. This review comprehensively explores the recent development of innovative CNT patterning techniques with nanoscale lateral resolution. Each technique is critically analyzed and applications for the nanoscale-resolution approaches are demonstrated. Promising techniques and the challenges ahead for future devices and applications are discussed.

All-solid-state flexible supercapacitor based on nanotube-reinforced polypyrrole hollowed structures

Nanotube-reinforced polypyrrole nanowires with hollowed cavities allow the fabrication of a flexible supercapacitor with a large specific capacitance.

Predictive Model for the Electrical Transport within Nanowire Networks

Thin networks of high aspect ratio conductive nanowires can combine high electrical conductivity with excellent optical transparency, which has led to a widespread use of nanowires in transparent electrodes, transistors, sensors, and flexible and stretchable conductors. Although the material and application aspects of conductive nanowire films have been thoroughly explored, there is still no model which can relate fundamental physical quantities, like wire resistance, contact resistance, and nanowire density, to the sheet resistance of the film. Here, we derive an analytical model for the electrical conduction within nanowire networks based on an analysis of the parallel resistor network. The model captures the transport characteristics and fits a wide range of experimental data, allowing for the determination of physical parameters and performance-limiting factors, in sharp contrast to the commonly employed percolation theory. The model thus constitutes a useful tool with predictive power for the evaluation and optimization of nanowire networks in various applications.

Multiplexed Biomolecular Arrays Generated via Parallel Dip-Pen Nanolithography

The capability of transferring target materials especially functionality-reliable biomolecules, into specific locations and with arbitrarily designed patterns are of critical importance for high-throughput disease diagnosis, multiplexing, and drug screening. Herein, we report the simultaneous patterning of two types of biomolecules using the parallel dip-pen nanolithography technology where an array of the atomic force microscope (AFM) tips can be selectively and alternately coated with target biomolecules via a specially designed inkwell array. Moreover, mixing target biomolecules at a proper volumetric ratio with polyethylene glycol dissolved in PBS buffer solution that works as an ink carrier can not only facilitate the smooth transfer of ink materials from the AFM tip to the substrate, it can also help to adjust the ink diffusion constant of different biomolecules to be highly similar so that the multiplexed biofunctional dot and/or line arrays at similar sizes can be reliably generated.

Elaborately programmed nanowires fabricated using a tapered push-pull nozzle system

Elaborately programmed silver nanowire arrays can be prepared using a tapered push-pull nozzle system (TPPNS), which is used to directly write micro-nano wires on a substrate via a two-reagent reaction in the diffusion mixing region. The wires could be precisely positioned on the substrate and their width could be freely controlled from the micro to the nano scale, indicating an advance in the methodologies of controlling and fabricating nanowires. The as-prepared silver three-electrode device can serve as a three-electrode sensor.

Bioelectronic Nose Using Olfactory Receptor-Embedded Nanodiscs

Olfactory receptors (ORs) are the largest family of the G protein-coupled receptors (GPCRs), which are significantly involved in many human diseases and 40% of all drug targets. A platform containing stable and high-quality OR would be a powerful tool for the development of a practical biosensor that can be applied to various applications, such as the early diagnosis of diseases, assessment of food quality, and drug and fragrance development. Significant efforts have been made to develop the biosensor using GPCRs; nevertheless, they remain a challenge. This chapter describes an attractive methodology for the development of a stable bioelectronic nose using OR-embedded nanodiscs. The ORs were produced in Escherichia coli (E. coli), purified with column chromatography, reconstituted into nanodiscs and applied to a carbon nanotube-field effect transistor (CNT-FET) with floating electrodes. The nanodisc-based bioelectronic nose exhibits high-performance in terms of sensitivity, selectivity and stability. This strategy can be used as a practical method for the receptor-based sensing approach, which represents significant progress in nano-bio technology toward a practical biosensor.

Precise Placement of Metallic Nanowires on a Substrate by Localized Electric Fields and Inter-Nanowire Electrostatic Interaction

Placing nanowires at the predetermined locations on a substrate represents one of the significant hurdles to be tackled for realization of heterogeneous nanowire systems. Here, we demonstrate spatially-controlled assembly of a single nanowire at the photolithographically recessed region at the electrode gap with high integration yield (~90%). Two popular routes, such as protruding electrode tips and recessed wells, for spatially-controlled nanowire alignment, are compared to investigate long-range dielectrophoretic nanowire attraction and short-range nanowire-nanowire electrostatic interaction for determining the final alignment of attracted nanowires. Furthermore, the post-assembly process has been developed and tested to make a robust electrical contact to the assembled nanowires, which removes any misaligned ones and connects the nanowires to the underlying electrodes of circuit.

High-Rate Assembly of Nanomaterials on Insulating Surfaces Using Electro-Fluidic Directed Assembly

Conductive or semiconducting nanomaterials-based applications such as electronics and sensors often require direct placement of such nanomaterials on insulating surfaces. Most fluidic-based directed assembly techniques on insulating surfaces utilize capillary force and evaporation but are diffusion limited and slow. Electrophoretic-based assembly, on the other hand, is fast but can only be utilized for assembly on a conductive surface. Here, we present a directed assembly technique that enables rapid assembly of nanomaterials on insulating surfaces. The approach leverages and combines fluidic and electrophoretic assembly by applying the electric field through an insulating surface via a conductive film underneath. The approach (called electro-fluidic) yields an assembly process that is 2 orders of magnitude faster compared to fluidic assembly. By understanding the forces on the assembly process, we have demonstrated the controlled assembly of various types of nanomaterials that are conducting, semiconducting, and insulating including nanoparticles and single-walled carbon nanotubes on insulating rigid and flexible substrates. The presented approach shows great promise for making practical devices in miniaturized sensors and flexible electronics.

Nanoscale hybrid systems based on carbon nanotubes for biological sensing and control

This paper provides a concise review on the recent development of nanoscale hybrid systems based on carbon nanotubes (CNTs) for biological sensing and control. CNT-based hybrid systems have been intensively studied for versatile applications of biological interfaces such as sensing, cell therapy and tissue regeneration. Recent advances in nanobiotechnology not only enable the fabrication of highly sensitive biosensors at nanoscale but also allow the applications in the controls of cell growth and differentiation. This review describes the fabrication methods of such CNT-based hybrid systems and their applications in biosensing and cell controls.

Bioelectronic Nose Using Odorant Binding Protein-Derived Peptide and Carbon Nanotube Field-Effect Transistor for the Assessment of Salmonella Contamination in Food

Salmonella infection is the one of the major causes of food borne illnesses including fever, abdominal pain, diarrhea, and nausea. Thus, early detection of Salmonella contamination is important for our healthy life. Conventional detection methods for the food contamination have limitations in sensitivity and rapidity; thus, the early detection has been difficult. Herein, we developed a bioelectronic nose using a carbon nanotube (CNT) field-effect transistor (FET) functionalized with Drosophila odorant binding protein (OBP)-derived peptide for easy and rapid detection of Salmonella contamination in ham. 3-Methyl-1-butanol is known as a specific volatile organic compound, generated from the ham contaminated with Salmonella. We designed and synthesized the peptide based on the sequence of the Drosophila OBP, LUSH, which specifically binds to alcohols. The C-terminus of the synthetic peptide was modified with three phenylalanine residues and directly immobilized onto CNT channels using the π-π interaction. The p-type properties of FET were clearly maintained after the functionalization using the peptide. The biosensor detected 1 fM of 3-methyl-1-butanol with high selectivity and successfully assessed Salmonella contamination in ham. These results indicate that the bioelectronic nose can be used for the rapid detection of Salmonella contamination in food.

Shape-Controlled Deterministic Assembly of Nanowires

Large-scale, deterministic assembly of nanowires and nanotubes with rationally controlled geometries could expand the potential applications of one-dimensional nanomaterials in bottom-up integrated nanodevice arrays and circuits. Control of the positions of straight nanowires and nanotubes has been achieved using several assembly methods, although simultaneous control of position and geometry has not been realized. Here, we demonstrate a new concept combining simultaneous assembly and guided shaping to achieve large-scale, high-precision shape controlled deterministic assembly of nanowires. We lithographically pattern U-shaped trenches and then shear transfer nanowires to the patterned substrate wafers, where the trenches serve to define the positions and shapes of transferred nanowires. Studies using semicircular trenches defined by electron-beam lithography yielded U-shaped nanowires with radii of curvature defined by inner surface of the trenches. Wafer-scale deterministic assembly produced U-shaped nanowires for >430,000 sites with a yield of ∼90%. In addition, mechanistic studies and simulations demonstrate that shaping results in primarily elastic deformation of the nanowires and show clearly the diameter-dependent limits achievable for accessible forces. Last, this approach was used to assemble U-shaped three-dimensional nanowire field-effect transistor bioprobe arrays containing 200 individually addressable nanodevices. By combining the strengths of wafer-scale top-down fabrication with diverse and tunable properties of one-dimensional building blocks in novel structural configurations, shape-controlled deterministic nanowire assembly is expected to enable new applications in many areas including nanobioelectronics and nanophotonics.

Nano-Bioelectronics

Nano-bioelectronics represents a rapidly expanding interdisciplinary field that combines nanomaterials with biology and electronics and, in so doing, offers the potential to overcome existing challenges in bioelectronics. In particular, shrinking electronic transducer dimensions to the nanoscale and making their properties appear more biological can yield significant improvements in the sensitivity and biocompatibility and thereby open up opportunities in fundamental biology and healthcare. This review emphasizes recent advances in nano-bioelectronics enabled with semiconductor nanostructures, including silicon nanowires, carbon nanotubes, and graphene. First, the synthesis and electrical properties of these nanomaterials are discussed in the context of bioelectronics. Second, affinity-based nano-bioelectronic sensors for highly sensitive analysis of biomolecules are reviewed. In these studies, semiconductor nanostructures as transistor-based biosensors are discussed from fundamental device behavior through sensing applications and future challenges. Third, the complex interface between nanoelectronics and living biological systems, from single cells to live animals, is reviewed. This discussion focuses on representative advances in electrophysiology enabled using semiconductor nanostructures and their nanoelectronic devices for cellular measurements through emerging work where arrays of nanoelectronic devices are incorporated within three-dimensional cell networks that define synthetic and natural tissues. Last, some challenges and exciting future opportunities are discussed.

Discrimination of Umami Tastants Using Floating Electrode-Based Bioelectronic Tongue Mimicking Insect Taste Systems

We report a floating electrode-based bioelectronic tongue mimicking insect taste systems for the detection and discrimination of umami substances. Here, carbon nanotube field-effect transistors with floating electrodes were hybridized with nanovesicles containing honeybee umami taste receptor, gustatory receptor 10 of Apis mellifera (AmGr10). This strategy enables us to discriminate between l-monosodium glutamate (MSG), best-known umami tastant, and non-umami substances with a high sensitivity and selectivity. It could also be utilized for the detection of MSG in liquid food such as chicken stock. Moreover, we demonstrated the synergism between MSG and disodium 5'-inosinate (IMP) for the umami taste using this platform. This floating electrode-based bioelectronic tongue mimicking insect taste systems can be a powerful platform for various applications such as food screening, and it also can provide valuable insights on insect taste systems.

Detection of airborne viruses using electro-aerodynamic deposition and a field-effect transistor

We report a technique for the detection of aerosolized viruses. Conventional field-effect-transistor (FET)-based techniques use solution-based processes, thus require antibody binding to the detection region of the FET prior to the supply of the analyte. With the method described here, virus-antibody-bound particles are delivered to the FET during detection; therefore, neither a pre-treatment antibody binding step on the FET channel nor washing process for virus-antibody-binding are necessary. Our method is based on the concept that virus-antibody-bound particles are larger than the virus or antibody alone, and thus have larger charge numbers following aerosol charging. When these particles are charged by negative ions and electro-aerodynamically deposited on a substrate, there exists a location on the substrate where neither lone virus nor antibody particles land, and where only virus-antibody-bound particles are deposited. If this location coincides with the channel of the FET, the resulting variation in the current can be used to indicate the existence of a virus. By aerosolizing a mixed solution of the virus and the antibody, only the virus-antibody-bound particles were transported to the swCNT-FET, and the electric current in the swCNT-FET decreased to 30% of that measured with no deposited particles.

Olfactory receptor screening assay using nanovesicle-immobilized carbon nanotube transistor

Olfactory receptor (OR) genes are considered to be the largest superfamily of the mammalian genome, and in the case of humans, approximately 390 kinds of functional ORs play a role in perceiving odors. In spite of their significance in olfaction, the function of all ORs has not yet been fully revealed. In order to efficiently identify specific ligands of orphan ORs, methods that can generate olfactory signals in a reliable manner and that can convert the cellular signals into measurable responses are required. Here, we describe an OR screening assay method using olfactory sensors that are based on cell-derived nanovesicles combined with single-walled carbon nanotube field-effect transistors (SWNT-FETs). The nanovesicles contain ORs on their surface membrane and induce influx of calcium ions similar to olfactory signal transduction. This ion influx causes an electrical current change along the carbon nanotube, and then this change is measured by the SWNT-FET sensor. This technique facilitates the simple and rapid screening of OR functions.

Patterned Threadlike Micelles and DNA-Tethered Nanoparticles: A Structural Study of PEGylated Cationic Liposome-DNA Assemblies

The self-assembly of oppositely charged biomacromolecules has been extensively studied due to its pertinence in the design of functional nanomaterials. Using cryo electron microscopy (cryo-EM), optical light scattering, and fluorescence microscopy, we investigated the structure and phase behavior of PEGylated (PEG: poly(ethylene glycol)) cationic liposome-DNA nanoparticles (CL-DNA NPs) as a function of DNA length, topology (linear and circular), and ρ(chg) (the molar charge ratio of cationic lipid to anionic DNA). Although all NPs studied exhibited lamellar internal nanostructure, NPs formed with short (∼2 kbps), linear, polydisperse DNA were defect-rich and contained smaller domains. Unexpectedly, we found distinctly different equilibrium structures away from the isoelectric point. At ρ(chg) > 1, in the excess cationic lipid regime, threadlike micelles rich in PEG-lipid were found to coexist with NPs, cationic liposomes, and spherical micelles. At high concentrations these PEGylated threadlike micelles formed a well-ordered, patterned morphology with highly uniform intermicellar spacing. At ρ(chg) < 1, in the excess DNA regime and with no added salt, individual NPs were tethered together via long, linear DNA (48 kbps λ-phage DNA) into a biopolymer-mediated floc. Our results provide insight into what equilibrium nanostructures can form when oppositely charged macromolecules self-assemble in aqueous media. Self-assembled, well-ordered threadlike micelles and tethered nanoparticles may have a broad range of applications in bionanotechnology, including nanoscale lithograpy and the development of lipid-based multifunctional nanoparticle networks.

Ion-channel-coupled receptor-based platform for a real-time measurement of G-protein-coupled receptor activities

A simple but efficient measurement platform based on ion-channel-coupled receptors and nanovesicles was developed for monitoring the real-time activity of G-protein-coupled receptors (GPCRs). In this work, an olfactory receptor (OR), the most common class A GPCR, was covalently fused with a Kir6.2 channel so that the GPCR action directly induced the opening of the ion channels and changes in the electrical membrane potential without complex cellular signaling processes. This strategy reduced the measurement errors caused by instability of various cellular components. In addition, rather than using whole cells, a cell-surface-derived nanovesicle was used to preserve the membrane-integrated structure of GPCRs and to exclude case-dependent cellular conditions. Another merit of using the nanovesicle is that nanovesicles can be easily combined with nanomaterial-based field-effect transistors (FETs) to build a sensitive and stable measurement platform to monitor GPCR activities with high sensitivity in real-time. Using a platform based on carbon nanotube FETs and nanovesicles carrying Kir6.2-channel-coupled ORs, we monitored the real-time response of ORs to their ligand molecules. Significantly, since this platform does not rely on rather unstable cell signaling pathways, our platform could be utilized for a rather long time period without losing its functionality. This system can be utilized extensively for simple and sensitive analysis of the activities of various GPCRs and should enable various academic and practical applications.

High-density metallic nanogap arrays for the sensitive detection of single-walled carbon nanotube thin films

We have investigated the extraordinary optical transmission of terahertz waves through an array of nanogaps with varying dimensions and periodicities, and used this platform to demonstrate terahertz sensing of a thin film of single-walled carbon nanotubes. We have used atomic layer lithography to fabricate periodic arrays of nanogap loops that have a gap size of 2 nm and a loop length of 100 μm (aspect ratio of 50 000). These sub-mm-scale loops of nanogaps can sustain terahertz electromagnetic resonances along the contour. We have characterized the transmission of terahertz waves through the nanogap arrays and investigated the influence of inter-gap electromagnetic coupling as the array periodicity shrinks from 100 μm to 4 μm. While the gaps occupy only 0.1% of the surface area, we have measured an amplitude (|E|) transmittance of over 50% due to the strong and broadband field enhancement inside the nanogaps. The absolute transmission through the 2 nm gaps along the rectangular loops can be boosted up to 25%, while it is only 1% for annular gaps with the same perimeter. Furthermore, the extremely tight field confinement and strong field enhancement near the 2 nm gap lead to 43% extinction of THz waves in a 10 nm-thick film of single-walled carbon nanotubes over the gaps. On the other hand, THz extinction by the same nanotube film on a bare glass substrate is only 2%. These nanogaps pave the way toward developing sensitive terahertz detectors for biological and chemical targets.

Real-time selective monitoring of allergenic Aspergillus molds using pentameric antibody-immobilized single-walled carbon nanotube-field effect transistors

A SWNT-FET directly functionalized with immunoglobulin M shows a wide detection range from sub-picomolar to micromolar with an excellent sensitivity due to chemical gating in selective monitoring of fungal allergens.

Electrical and optical polarization responses of composite films based on aligned carbon nanotubes

A simple and efficient approach for large-area preparation of horizontally-aligned carbon nanotube (CNT)–vanadium oxide (VO_x) composite films is presented. The as-prepared composite films particularly exhibit electrical and optical anisotropies.

Directed assembly of nanodiamond nitrogen-vacancy centers on a chemically modified patterned surface

Nitrogen-vacancy (NV) centers in nanodiamond (ND) particles are an attractive material for photonic, quantum information, and biological sensing technologies due to their optical properties-bright single photon emission and long spin coherence time. To harness these features in practical devices, it is essential to realize efficient methods to assemble and pattern NDs at the micro-/nanoscale. In this work, we report the large scale patterned assembly of NDs on a Au surface by creating hydrophobic and hydrophilic regions using self-assembled monolayer (SAM). Hydrophobic regions are created using a methyl (-CH3) terminated SAM of octadecanethiol molecules. Evaporating a water droplet suspension of NDs on the SAM patterned surface assembles the NDs in the bare Au, hydrophilic regions. Using this procedure, we successfully produced a ND structures in the shape of dots, lines, and rectangles. Subsequent photoluminescence imaging of the patterned NDs confirmed the presence of optically active NV centers. Experimental evidence in conjunction with computational analysis indicates that the surface wettability of the SAM modified Au surface plays a dominant role in the assembly of NDs as compared to van der Waals and other substrate-ND interactions.

Soluble polymer-based, blown bubble assembly of single- and double-layer nanowires with shape control

We present here an efficient blown bubble method for large-scale assembly of semiconducting nanowires, with simultaneous control on the material shape. As-synthesized Te nanowires in powder form are dispersed in a polymethylmethacrylate (PMMA) solution, assembled in a large size bubble blown from the solution, and then transferred (repeatedly) to arbitrary substrates. By this way, we have obtained single-layer (aligned) and double-layer (crossed) Te nanowires as well as buckled Te nanosprings which are converted from initially straight nanowires in situ during bubble blowing. The PMMA bubble film can be removed by direct dissolution in acetone to expose nanostructures with clean surface while maintaining original configuration. After matrix removal, these clean nanowire and nanospring arrays can be fabricated into functional nanoelectronic devices such as photodetectors and gas sensors with high performance.

Nanovesicle-based bioelectronic nose for the diagnosis of lung cancer from human blood

A human nose-mimetic diagnosis system that can distinguish the odor of a lung cancer biomarker, heptanal, from human blood is presented. Selective recognition of the biomarker is mimicked in the human olfactory system. A specific olfactory receptor recognizing the chemical biomarker is first selected through screening a library of human olfactory receptors (hORs). The selected hOR is expressed on the membrane of human embryonic kidney (HEK)-293 cells. Nanovesicles containing the hOR on the membrane are produced from these cells, and are then used for the functionalization of single-walled carbon nanotubes. This strategy allows the development of a sensitive and selective nanovesicle-based bioelectronic nose (NvBN). The NvBN is able to selectively detect heptanal at a concentration as low as 1 × 10(-14) m, a sufficient level to distinguish the blood of a lung cancer patient from the blood of a healthy person. In actual experiments, NvBN could detect an extremely small increase in the amount of heptanal from human blood plasma without any pretreatment processes. This result offers a rapid and easy method to analyze chemical biomarkers from human blood in real-time and to diagnose lung cancer.

Functional characterization of naturally occurring melittin peptide isoforms in two honey bee species, Apis mellifera and Apis cerana

Insect-derived antimicrobial peptides (AMPs) have diverse effects on antimicrobial properties and pharmacological activities such as anti-inflammation and anticancer properties. Naturally occurring genetic polymorphism have a direct and/or indirect influence on pharmacological effect of AMPs, therefore information on single nucleotide polymorphism (SNP) occurring in natural AMPs provides an important clue to therapeutic applications. Here we identified nucleotide polymorphisms in melittin gene of honey bee populations, which is one of the potent AMP in bee venoms. We found that the novel SNP of melittin gene exists in these two honey bee species, Apis mellifera and Apis cerana. Nine polymorphisms were identified within the coding region of the melittin gene, of which one polymorphism that resulted in serine (Ser) to asparagine (Asp) substitution that can potentially effect on biological activities of melittin peptide. Serine-substituted melittin (Mel-S) showed more cytotoxic effect than asparagine-substituted melittin (Mel-N) against E. coli. Also, Mel-N and Mel-S had different inhibitory effects on the production of inflammatory factors such as IL-6 and TNF-α in BV-2 cells. Moreover, Mel-S showed stronger cytotoxic activities than Mel-N peptide against two human ovarian cancer cell lines. Using carbon nanotube-based transistor, we here characterized that Mel-S interacted with small unilamellar liposomes more strongly than Mel-N. Taken together, our present study demonstrates that there exist different characteristics of the gene frequency and the biological activities of the melittin peptide in two honey bee species, Apis mellifera and A. cerana.

Single-walled carbon nanotubes for high-performance electronics

Single-walled carbon nanotubes (SWNT) could replace silicon in high-performance electronics with their exceptional electrical properties and intrinsic ultra-thin body. During the past five years, the major focus of this field is gradually shifting from proof-of-concept prototyping in academia to technology development in industry with emphasis on manufacturability and integration issues. This article reviews recent advances, starting with experimental and modeling works that evaluate the potential of adopting SWNTs in ultimately scaled transistors. Techniques to separate nanotubes according to their electronic types and assemble them into aligned arrays are then discussed, followed by a description of the engineering aspects in their implementation in integrated circuits and systems. A concluding discussion provides some perspectives on future challenges and research opportunities.

Graphene nanonet for biological sensing applications

We report a simple but efficient method to fabricate versatile graphene nanonet (GNN)-devices. In this method, networks of V2O5 nanowires (NWs) were prepared in specific regions of single-layer graphene, and the graphene layer was selectively etched via a reactive ion etching method using the V2O5 NWs as a shadow mask. The process allowed us to prepare large scale patterns of GNN structures which were comprised of continuous networks of graphene nanoribbons (GNRs) with chemical functional groups on their edges. The GNN can be easily functionalized with biomolecules for fluorescent biochip applications. Furthermore, electrical channels based on GNN exhibited a rather high mobility and low noise compared with other network structures based on nanostructures such as carbon nanotubes, which was attributed to the continuous connection of nanoribbons in GNN structures. As a proof of concept, we built DNA sensors based on GNN channels and demonstrated the selective detection of DNA. Since our method allows us to prepare high-performance networks of GNRs over a large surface area, it should open up various practical biosensing applications.

High-density integration of carbon nanotubes via chemical self-assembly

Carbon nanotubes have potential in the development of high-speed and power-efficient logic applications. However, for such technologies to be viable, a high density of semiconducting nanotubes must be placed at precise locations on a substrate. Here, we show that ion-exchange chemistry can be used to fabricate arrays of individually positioned carbon nanotubes with a density as high as 1 × 10(9) cm(-2)-two orders of magnitude higher than previous reports. With this approach, we assembled a high density of carbon-nanotube transistors in a conventional semiconductor fabrication line and then electrically tested more than 10,000 devices in a single chip. The ability to characterize such large distributions of nanotube devices is crucial for analysing transistor performance, yield and semiconducting nanotube purity.

A peptide receptor-based bioelectronic nose for the real-time determination of seafood quality

We herein report a peptide receptor-based bioelectronic nose (PRBN) that can determine the quality of seafood in real-time through measuring the amount of trimethylamine (TMA) generated from spoiled seafood. The PRBN was developed using single walled-carbon nanotube field-effect transistors (SWNT-FETs) functionalized with olfactory receptor-derived peptides (ORPs) which can recognize TMA and it allowed us to sensitively and selectively detect TMA in real-time at concentrations as low as 10fM. Utilizing these properties, we were able to not only determine the quality of three kinds of seafood (oyster, shrimp, and lobster), but were also able to distinguish spoiled seafood from other types of spoiled foods without any pretreatment processes. Especially, the use of small synthetic peptide rather than the whole protein allowed PRBNs to be simply manufactured through a single-step process and to be reused with high reproducibility due to no requirement of lipid bilayers. Furthermore, the PRBN was produced on a portable scale making it effectively useful for the food industry where the on-site measurement of seafood quality is required.

High-performance photoconductive channels based on (carbon nanotube)-(CdS nanowire) hybrid nanostructures

A photoconductive channel based on hybrid nanostructures comprising carbon nanotubes (CNTs) and CdS nanowires is fabricated by a directed assembly strategy and catalyst-assisted chemical vapor deposition (CVD). The photoconductive channels simultaneously exhibit large photocurrent and fast response speed. Furthermore, it can be easily applied to surfaces that are not flat, such as a glass tube. This is a simple but efficient strategy for various optoelectronic applications.

Ultrasensitive detection of the reduced form of nicotinamide adenine dinucleotide based on carbon nanotube field effect transistor

We developed a simple, ultrasensitive, and quantitative detection method for the reduced form of nicotinamide adenine dinucleotide (NADH), based on carbon nanotube field effect transistors (CNTFETs). Following the injection of NADH at different concentrations, we obtained different electrical signals from a semiconductor characterization system mimicking biological catalysis of NADH dehydrogenase (CoI). Here, FET was fabricated via photolithography, attaching silicon wells, as the detection chamber, on the channel area of the single wall carbon nanotube (SWCNT). SWCNTs were functionalized with phenazine derivant, a counterpart of the key functional prosthetic group of CoI enzyme. In the presence of NADH, electrons transferred to phenazine derivant through SWCNT, by analogous means of the electron transport chain formed by a series of iron-sulfur (FeS) clusters in CoI. Using this method, the limit of detection was as low as 1 pM, and the range of linear response was 10 pM to 500 nM. Significantly, this approach possesses great potential for applications in real-time detection of NADH at extremely low concentrations, and rigorous analysis for NADH in electrochemical fields.

A bioelectronic sensor based on canine olfactory nanovesicle-carbon nanotube hybrid structures for the fast assessment of food quality

We developed an olfactory-nanovesicle-fused carbon-nanotube-transistor biosensor (OCB) that mimics the responses of a canine nose for the sensitive and selective detection of hexanal, an indicator of the oxidation of food. OCBs allowed us to detect hexanal down to 1 fM concentration in real-time. Significantly, we demonstrated the detection of hexanal with an excellent selectivity capable of discriminating hexanal from analogous compounds such as pentanal, heptanal, and octanal. Furthermore, we successfully detected hexanal in spoiled milk without any pretreatment processes. Considering these results, our sensor platform should offer a new method for the assessment of food quality and contribute to the development of portable sensing devices.

Nanotube-bridged wires with sub-10 nm gaps

We report a simple but efficient method to synthesize carbon nanotube-bridged wires (NBWs) with gaps as small as 5 nm. In this method, we have combined a strategy for assembling carbon nanotubes (CNTs) inside anodized aluminum oxide pores and the on-wire lithography technique to fabricate CNT-bridged wires with gap sizes deliberately tailored over the 5-600 nm range. As a proof-of-concept demonstration of the utility of this architecture, we have prepared NBW-based chemical and biosensors which exhibit higher analyte sensitivity (lower limits of detection) than those based on planar CNT networks. This observation is attributed to a greater surface-to-volume ratio of CNTs in the NBWs than those in the planar CNT devices. Because of the ease of synthesis and high yield of NBWs, this technique may enable the further incorporation of CNT-based architectures into various nanoelectronic and sensor platforms.

SWNT ensembles with porphyrins and phthalocyanines: new architectures for energy conversion

This paper presents the work developed in Spain, in collaboration with other European groups, on the synthesis and photovoltaic applications of hybrid systems comprised of single-walled nanotubes linked to either phthalocyanine or porphyrin moieties.

Nanovesicle-based bioelectronic nose platform mimicking human olfactory signal transduction

We developed a nanovesicle-based bioelectronic nose (NBN) that could recognize a specific odorant and mimic the receptor-mediated signal transmission of human olfactory systems. To build an NBN, we combined a single-walled carbon nanotube-based field effect transistor with cell-derived nanovesicles containing human olfactory receptors and calcium ion signal pathways. Importantly, the NBN took advantages of cell signal pathways for sensing signal amplification, enabling ≈ 100 times better sensitivity than that of previous bioelectronic noses based on only olfactory receptor protein and carbon nanotube transistors. The NBN sensors exhibited a human-like selectivity with single-carbon-atomic resolution and a high sensitivity of 1 fM detection limit. Moreover, this sensor platform could mimic a receptor-meditated cellular signal transmission in live cells. This sensor platform can be utilized for the study of molecular recognition and biological processes occurring at cell membranes and also for various practical applications such as food screening and medical diagnostics.

DNA-linker-induced surface assembly of ultra dense parallel single walled carbon nanotube arrays

Ultrathin film preparations of single-walled carbon nanotube (SWNT) allow economical utilization of nanotube properties in electronics applications. Recent advances have enabled production of micrometer scale SWNT transistors and sensors but scaling these devices down to the nanoscale, and improving the coupling of SWNTs to other nanoscale components, may require techniques that can generate a greater degree of nanoscale geometric order than has thus far been achieved. Here, we introduce linker-induced surface assembly, a new technique that uses small structured DNA linkers to assemble solution dispersed nanotubes into parallel arrays on charged surfaces. Parts of our linkers act as spacers to precisely control the internanotube separation distance down to <3 nm and can serve as scaffolds to position components such as proteins between adjacent parallel nanotubes. The resulting arrays can then be stamped onto other substrates. Our results demonstrate a new paradigm for the self-assembly of anisotropic colloidal nanomaterials into ordered structures and provide a potentially simple, low cost, and scalable route for preparation of exquisitely structured parallel SWNT films with applications in high-performance nanoscale switches, sensors, and meta-materials.

Ion-selective controlled assembly of dendrimer-based functional nanofibers and their ionic-competitive disassembly

The construction of hierarchical materials through controlled self-assembly of molecular building blocks (e.g., dendrimers) represents a unique opportunity to generate functional nanodevices in a convenient way. Transition-metal compounds are known to be able to interact with cationic dendrimers to generate diverse supramolecular structures, such as nanofibers, with interesting collective properties. In this work, molecular dynamics simulation (MD) demonstrates that acetate ions from dissociated Cd(CH(3)COO)(2) selectively generate cationic PPI-dendrimer functional fibers through hydrophobic modification of the dendrimer's surface. The hydrophobic aggregation of dendrimers is triggered by the asymmetric nature of the acetate anions (AcO(-)) rather than by the precise transition metal (Cd). The assembling directionality is also controlled by the concentration of AcO(-) ions in solution. Atomic force (AFM) and transmission electron microscopy (TEM) prove these results. This well-defined directional assembly of cationic dendrimers is absent for different cadmium derivatives (i.e., CdCl(2), CdSO(4)) with symmetric anions. Moreover, since the formation of these nanofibers is controlled exclusively by selected anions, fiber disassembly can be consequently triggered via simple ionic competition by NaCl salt. Ions are here reported as a simple and cost-effective tool to drive and control actively the assembly and the disassembly of such functional nanomaterials based on dendrimers.