Transistor probes local potassium conductances in the adhesion region of cultured rat hippocampal neurons.
Adhesion interactions of neurons in a tissue may affect the ion conductance of the plasma membrane, inducing selective localization and modulation of channels. We studied the adhesion region of cultured neurons from rat hippocampus as a defined model where such effects could be observed electrophysiologically, taking advantage of extracellular recording by a transistor integrated in the substrate. We observed the K(+) current through the region of soma adhesion under voltage-clamp and compared it with the current through the whole cell. We found that the specific A-type conductance was depleted, even completely, in the region of adhesion, whereas the specific K-type conductance was enhanced up to a factor of 12. The electrophysiological approach opens a new way to investigate targeting of ion channels in the cell membrane as a function of adhesion processes. (+info)
The combination of their electronic properties and dimensions makes carbon nanotubes ideal building blocks for molecular electronics. However, the advancement of carbon nanotube-based electronics requires assembly strategies that allow their precise localization and interconnection. Using a scheme based on recognition between molecular building blocks, we report the realization of a self-assembled carbon nanotube field-effect transistor operating at room temperature. A DNA scaffold molecule provides the address for precise localization of a semiconducting single-wall carbon nanotube as well as the template for the extended metallic wires contacting it. (+info)
A large-area, flexible pressure sensor matrix with organic field-effect transistors for artificial skin applications.
It is now widely accepted that skin sensitivity will be very important for future robots used by humans in daily life for housekeeping and entertainment purposes. Despite this fact, relatively little progress has been made in the field of pressure recognition compared to the areas of sight and voice recognition, mainly because good artificial "electronic skin" with a large area and mechanical flexibility is not yet available. The fabrication of a sensitive skin consisting of thousands of pressure sensors would require a flexible switching matrix that cannot be realized with present silicon-based electronics. Organic field-effect transistors can substitute for such conventional electronics because organic circuits are inherently flexible and potentially ultralow in cost even for a large area. Thus, integration of organic transistors and rubber pressure sensors, both of which can be produced by low-cost processing technology such as large-area printing technology, will provide an ideal solution to realize a practical artificial skin, whose feasibility has been demonstrated in this paper. Pressure images have been taken by flexible active matrix drivers with organic transistors whose mobility reaches as high as 1.4 cm(2)/V.s. The device is electrically functional even when it is wrapped around a cylindrical bar with a 2-mm radius. (+info)
Sigma-pi molecular dielectric multilayers for low-voltage organic thin-film transistors.
Very thin (2.3-5.5 nm) self-assembled organic dielectric multilayers have been integrated into organic thin-film transistor structures to achieve sub-1-V operating characteristics. These new dielectrics are fabricated by means of layer-by-layer solution phase deposition of molecular silicon precursors, resulting in smooth, nanostructurally well defined, strongly adherent, thermally stable, virtually pinhole-free, organosiloxane thin films having exceptionally large electrical capacitances (up to approximately 2,500 nF.cm(-2)), excellent insulating properties (leakage current densities as low as 10(-9) A.cm(-2)), and single-layer dielectric constant (k)of approximately 16. These 3D self-assembled multilayers enable organic thin-film transistor function at very low source-drain, gate, and threshold voltages (<1 V) and are compatible with a broad variety of vapor- or solution-deposited p- and n-channel organic semiconductors. (+info)
Cell-transistor coupling: investigation of potassium currents recorded with p- and n-channel FETs.
Microelectronic-based biosensors that allow noninvasive measurement of cell activity are in the focus of current developments, however, the mechanisms underlying the cell-transistor coupling are not completely understood. In particular, characteristic properties of the extracellular voltage response such as the waveform and amplitude are not satisfactorily described by electrical circuit models. Here we examine the electrical coupling between a nonmetallized field-effect transistor (FET) and a cell line expressing a voltage-gated EAG K+ channel. The activation kinetics of this channel depends on the voltage pulse protocol and extracellular divalent cations. This feature allows testing, whether the extracellular voltage signal recorded with the FET faithfully tracks the current simultaneously recorded with the patch-clamp technique. We find that the FET signals contain different kinetic components that cannot be entirely explained by equivalent electrical-circuit models. Rather, we suggest that changes in ion concentration in the small cleft between cell and FET may change the surface potential of the FET. This study provides evidence that the electrochemical processes at the cell-transistor interface are complex and that at least two different mechanisms contribute to the shape and amplitude of transistor signals. (+info)
Conformable, flexible, large-area networks of pressure and thermal sensors with organic transistor active matrixes.
Skin-like sensitivity, or the capability to recognize tactile information, will be an essential feature of future generations of robots, enabling them to operate in unstructured environments. Recently developed large-area pressure sensors made with organic transistors have been proposed for electronic artificial skin (E-skin) applications. These sensors are bendable down to a 2-mm radius, a size that is sufficiently small for the fabrication of human-sized robot fingers. Natural human skin, however, is far more complex than the transistor-based imitations demonstrated so far. It performs other functions, including thermal sensing. Furthermore, without conformability, the application of E-skin on three-dimensional surfaces is impossible. In this work, we have successfully developed conformable, flexible, large-area networks of thermal and pressure sensors based on an organic semiconductor. A plastic film with organic transistor-based electronic circuits is processed to form a net-shaped structure, which allows the E-skin films to be extended by 25%. The net-shaped pressure sensor matrix was attached to the surface of an egg, and pressure images were successfully obtained in this configuration. Then, a similar network of thermal sensors was developed with organic semiconductors. Next, the possible implementation of both pressure and thermal sensors on the surfaces is presented, and, by means of laminated sensor networks, the distributions of pressure and temperature are simultaneously obtained. (+info)
Functional Na+ channels in cell adhesion probed by transistor recording.
Cell membranes in a tissue are in close contact to each other, embedded in the extracellular matrix. Standard electrophysiological methods are not able to characterize ion channels under these conditions. Here we consider the area of cell adhesion on a solid substrate as a model system. We used HEK 293 cells cultured on fibronectin and studied the activation of Na(V)1.4 sodium channels in the adherent membrane with field-effect transistors in a silicon substrate. Under voltage clamp, we compared the transistor response with the whole-cell current. We observed that the extracellular voltage in the cell-chip contact was proportional to the total membrane current. The relation was calibrated by alternating-current stimulation. We found that Na(+) channels are present in the area of cell adhesion on fibronectin with a functionality and a density that is indistinguishable from the free membrane. The experiment provides a basis for studying selective accumulation and depletion of ion channels in cell adhesion and also for a development of cell-based biosensoric devices and neuroelectronic systems. (+info)
Quantum criticality in ferromagnetic single-electron transistors.
Considerable evidence exists for the failure of the traditional theory of quantum critical points, pointing to the need to incorporate novel excitations. The destruction of Kondo entanglement and the concomitant critical Kondo effect may underlie these emergent excitations in heavy fermion metals (a prototype system for quantum criticality), but the effect remains poorly understood. Here, we show how ferromagnetic single-electron transistors can be used to study this effect. We theoretically demonstrate a gate-voltage-induced quantum phase transition. The critical Kondo effect is manifested in a fractional-power-law dependence of the conductance on temperature (T). The AC conductance and thermal noise spectrum have related power-law dependences on frequency (omega) and, in addition, show an omega/T scaling. Our results imply that the ferromagnetic nanostructure constitutes a realistic model system to elucidate magnetic quantum criticality that is central to the heavy fermions and other bulk materials with non-Fermi liquid behavior. (+info)