Mapping nanoscale effects of localized noise-source activities on photoconductive charge transports in polymer-blend films.

We develolped a method to directly image the nanoscale effects of localized noise-source activities on photoconducting charge transports in domain structures of phase-separated polymer-blend films of Poly(9,9-di-n-octylfluorenyl-2,7-diyl) and Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole). For the imaging, current and noise maps of the polymer-blend were recorded using a conducting nanoprobe in contact with the surface, enabling the conductivity (σ) and noise-source density (N T) mappings under an external stimulus. The blend-films exhibited the phase-separation between the constituent polymers at domains level. Within a domain, high σ (low N T) and low σ (high N T) regions were observed, which could be associated with the ordered and disordered regions of a domain. In the N T maps, we observed that noise-sources strongly affected the conduction mechanism, resulting in a scaling behavior of σ âˆ [Formula: see text] in both ordered and disordered regions. When a blend film was under an influence of an external stimulus such as a high bias or an illumination, an increase in the σ was observed, but that also resulted in increases in the N T as a trade-off. Interestingly, the Δσ versus ΔN T plot exhibited an unusual scaling behavior of Δσ âˆ [Formula: see text] which is attributed to the de-trapping of carriers from deep traps by the external stimuli. In addition, we found that an external stimulus increased the conductivity at the interfaces without significantly increasing their N T, which can be the origin of the superior performances of polymer-blend based devices. These results provide valuable insight about the effects of noise-sources on nanoscale optoelectronic properties in polymer-blend films, which can be an important guideline for improving devices based on polymer-blend.

Nanoscale anomalous noise source switching with a trap-free current transition in a PEDOT:PSS film.

We imaged localized charge traps in a PEDOT:PSS film by using a scanning noise microscopy (SNM) system and observed anomalous noise source switching behaviors affecting the electrical characteristics of the film. The SNM system enabled us to measure the localized electrical current and noise maps of a PEDOT:PSS film with nanoscale resolution. The measured maps of the currents and noises were utilized to calculate effective charge trap densities in the film. As a result, we found non-homogeneous distributions of currents and effective charge trap densities on the localized area of the film due to the non-uniform distribution of PEDOT-rich and PSS-rich grains. At a low bias voltage, we observed high current levels and high charge trap densities in PEDOT-rich grains, while PSS-rich grains showed low-current levels and charge trap densities. Interestingly, the charge trap densities in both grains showed a noise source switching behavior with respect to the applied bias voltages, and the behavior strongly affected their electrical characteristic such as the trap-free transition of currents. These results indicate that the charge traps in a PEDOT:PSS film play an important role in the electrical characteristics of the films. Our observations provide a valuable insight on the understanding of the electrical characteristics of PEDOT:PSS films and an important guideline for its practical applications.

High-Speed Lateral Flow Strategy for a Fast Biosensing with an Improved Selectivity and Binding Affinity.

We report a high-speed lateral flow strategy for a fast biosensing with an improved selectivity and binding affinity even under harsh conditions. In this strategy, biosensors were fixed at a location away from the center of a round shape disk, and the disk was rotated to create the lateral flow of a target solution on the biosensors during the sensing measurements. Experimental results using the strategy showed high reaction speeds, high binding affinity, and low nonspecific adsorptions of target molecules to biosensors. Furthermore, binding affinity between target molecules and sensing molecules was enhanced even in harsh conditions such as low pH and low ionic strength conditions. These results show that the strategy can improve the performance of conventional biosensors by generating high-speed lateral flows on a biosensor surface. Therefore, our strategy can be utilized as a simple but powerful tool for versatile bio and medical applications.

Magnetically-refreshable receptor platform structures for reusable nano-biosensor chips.

We developed a magnetically-refreshable receptor platform structure which can be integrated with quite versatile nano-biosensor structures to build reusable nano-biosensor chips. This structure allows one to easily remove used receptor molecules from a biosensor surface and reuse the biosensor for repeated sensing operations. Using this structure, we demonstrated reusable immunofluorescence biosensors. Significantly, since our method allows one to place receptor molecules very close to a nano-biosensor surface, it can be utilized to build reusable carbon nanotube transistor-based biosensors which require receptor molecules within a Debye length from the sensor surface. Furthermore, we also show that a single sensor chip can be utilized to detect two different target molecules simply by replacing receptor molecules using our method. Since this method does not rely on any chemical reaction to refresh sensor chips, it can be utilized for versatile biosensor structures and virtually-general receptor molecular species.

Carbon and metal nanotube hybrid structures on graphene as efficient electron field emitters.

We report a facile and efficient method for the fabrication of highly-flexible field emission devices by forming tubular hybrid structures based on carbon nanotubes (CNTs) and nickel nanotubes (Ni NTs) on graphene-based flexible substrates. By employing an infiltration process in anodic alumina oxide (AAO) templates followed by Ni electrodeposition, we could fabricate CNT-wrapped Ni NT/graphene hybrid structures. During the electrodeposition process, the CNTs served as Ni nucleation sites, resulting in a large-area array of high aspect-ratio field emitters composed of CNT-wrapped Ni NT hybrid structures. As a proof of concepts, we demonstrate that high-quality flexible field emission devices can be simply fabricated using our method. Remarkably, our proto-type field emission devices exhibited a current density higher by two orders of magnitude compared to other devices fabricated by previous methods, while maintaining its structural integrity in various bending deformations. This novel fabrication strategy can be utilized in various applications such as optoelectronic devices, sensors and energy storage devices.

Nafion-Radical Hybrid Films on Carbon Nanotube Transistors for Monitoring Antipsychotic Drug Effects on Stimulated Dopamine Release.

We developed floating electrode-based carbon nanotube biosensors for the monitoring of antipsychotic drug effects on the dopamine release from PC12 cells under potassium stimulation. Here, carbon nanotube field-effect transistors with floating electrodes were functionalized with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•) radicals by Nafion films. This method allows us to build selective biosensors for dopamine detection with a detection limit down to 10 nM even in the presence of other neurotransmitters such as glutamate and acetylcholine, resulting from the selective interaction between ABTS• radicals and dopamine. The sensors were also utilized to monitor the real-time release of dopamine from PC12 cells upon the stimulation of high-concentrated potassium solutions. Significantly, the antipsychotic effects of pimozide on the dopamine release from potassium-stimulated PC12 cells could also be evaluated in a concentration-dependent manner by using the sensors. The quantitative and real-time evaluation capability of our strategy should provide a versatile tool for many biomedical studies and applications.

Quantitative electrophysiological monitoring of anti-histamine drug effects on live cells via reusable sensor platforms.

We demonstrated the quantitative electrophysiological monitoring of histamine and anti-histamine drug effects on live cells via reusable sensor platforms based on carbon nanotube transistors. This method enabled us to monitor the real-time electrophysiological responses of a single HeLa cell to histamine with different concentrations. The measured electrophysiological responses were attributed to the activity of histamine type 1 receptors on a HeLa cell membrane by histamine. Furthermore, the effects of anti-histamine drugs such as cetirizine or chlorphenamine on the electrophysiological activities of HeLa cells were also evaluated quantitatively. Significantly, we utilized only a single device to monitor the responses of multiple HeLa cells to each drug, which allowed us to quantitatively analyze the antihistamine drug effects on live cells without errors from the device-to-device variation in device characteristics. Such quantitative evaluation capability of our method would promise versatile applications such as drug screening and nanoscale bio sensor researches.

Nanoscale direct mapping of localized and induced noise sources on conducting polymer films.

The localized noise-sources and those induced by external-stimuli were directly mapped by using a conducting-AFM integrated with a custom-designed noise measurement set-up. In this method, current and noise images of a poly(9,9-dioctylfluorene)-polymer-film on a conducting-substrate were recorded simultaneously, enabling the mapping of the resistivity and noise source density (NT). The polymer-films exhibited separate regions with high or low resistivities, which were attributed to the ordered or disordered phases, respectively. A larger number of noise-sources were observed in the disordered-phase-regions than in the ordered-phase regions, due to structural disordering. Increased bias-voltages on the disordered-phase-regions resulted in increased NT, which is explained by the structural deformation at high bias-voltages. On photo-illumination, the ordered-phase-regions exhibited a rather large increase in the conductivity and NT. Presumably, the illumination released carriers from deep-traps which should work as additional noise-sources. These results show that our methods provide valuable insights into noise-sources and, thus, can be powerful tools for basic research and practical applications of conducting polymer films.

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.

Real-time monitoring of geosmin and 2-methylisoborneol, representative odor compounds in water pollution using bioelectronic nose with human-like performance.

A bioelectronic nose for the real-time assessment of water quality was constructed with human olfactory receptor (hOR) and single-walled carbon nanotube field-effect transistor (swCNT-FET). Geosmin (GSM) and 2-methylisoborneol (MIB), mainly produced by bacteria, are representative odor compounds and also indicators of contamination in the water supply system. For the screening of hORs which respond to these compounds, we performed CRE-luciferase assays of the two odorants in heterologous cell system. Human OR51S1 for GSM and OR3A4 for MIB were selected, and nanovesicles expressing the hORs on surface were produced from HEK-293 cell. Carbon nanotube field-effect transistor was functionalized with the nanovesicles. The bioelectronic nose was able to selectively detect GSM and MIB at concentrations as low as a 10 ng L(-1). Furthermore, detection of these compounds from the real samples such as tap water, bottled water and river water was available without any pretreatment processes.

Nanovesicle-based platform for the electrophysiological monitoring of aquaporin-4 and the real-time detection of its antibody.

Aquaporin-4 (AQP4) water channel protein transports water molecules across cell membranes bidirectionally and involves in a neurological disorder, neuromyelitis optica (NMO) caused by anti-AQP4 antibodies. Here, we developed a platform based on nanovesicle-carbon nanotube hybrid nanostructures for the real-time detection of anti-AQP4 antibodies and the electrophysiological monitoring of AQP4 activities. Using the hybrid device, we could detect anti-AQP4 antibodies with a high sensitivity and estimate the binding constants under different osmotic conditions. The results show AQP4 had a better affinity to anti-AQP4 antibodies under hyper-osmotic conditions than normal conditions. Furthermore, our device can be utilized to study the real-time cellular responses related with AQP4 such as those to different osmotic stresses. This nanovesicle-based platform can be a simple but versatile tool for basic research about AQP4 and related biomedical applications such as disease diagnostics.