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Herein, we introduce a method to simultaneously photoadhere a photocrosslinkable polymer to a plasma-treated fluoropolymer while photopatterning the photocrosslinkable polymer via a single-photo-exposure as a new electrode passivation technique. Photoadhesion was determined to result from plasma-generated radicals of the plasma-treated fluoropolymer. Crystallinity of the fluoropolymer was analysed to determine the photoadhesion strength through its effects on both the formation of radicals and the etching of fluoropolymers. Passivation feasibility of simultaneous photoadhesion and photopatterning (P&P) technique were demonstrated by fabricating an Au electrocorticography electrode array and modifying the electrode with electro-deposited metallic nanoparticles. Adhesion of sputter-deposited Au to the fluoropolymer was dependent on mechanical interlocking, indicated by the formation of Au clusters which are typically influenced by the surface temperature during the sputter-deposition and the glass transition temperature of the fluoropolymer. The adhesion of Au to the fluoropolymer without an additional adhesion promotor and the proposed P&P passivation technique would help prevent detachment of the electrode and the delamination of the passivation layer in fluoropolymer-based neural electrode.

Tetrodes, consisting of four twisted micro-wires can simultaneously record the number of neurons in the brain. To improve the quality of neuronal activity detection, the tetrode tips should be modified to increase the surface area and lower the impedance properties. In this study, tetrode tips were modified by the electrodeposition of Au nanoparticles (AuNPs) and dextran (Dex) doped poly (3,4-ethylenedioxythiophene) (PEDOT). The electrochemical properties were measured using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). A decrease in the impedance value from 4.3 MΩ to 13 kΩ at 1 kHz was achieved by the modified tetrodes. The cathodic charge storage capacity (CSCC) of AuNPs-PEDOT deposited tetrodes was 4.5 mC/cm2, as determined by CV measurements. The tetrodes that were electroplated with AuNPs and PEDOT exhibited an increased surface area, which reduced the tetrode impedance. In vivo recording in the ventral posterior medial (VPM) nucleus of the thalamus was performed to investigate the single-unit activity in normal rats. To evaluate the recording performance of modified tetrodes, spontaneous spike signals were recorded. The values of the L-ratio, isolation distance and signal-to-noise (SNR) confirmed that electroplating the tetrode surface with AuNPs and PEDOT improved the recording performance, and these parameters could be used to effectively quantify the spikes of each cluster., Graphical Abstract

All metal oxide heterostructured multielectrode arrays consisting of indium-tin oxide nanowires (ITO NWs) and an iridium oxide (IrO x ) layer were fabricated. The needle-type ITO NWs were grown on an ITO electrode using a radio frequency magnetron sputtering technique followed by electrodeposition of an IrO x layer. The major advantage of this fabrication technique is in its simplicity because it does not require templates and seed layers to grow the ITO NWs. A transmission electron microscope found the IrO x to be uniformly electrodeposited over the surface of the ITO NW. After the electrodeposition process, the charge storage capacitance (CSC) of the ITO NW electrode increased from 0.09 to 4.25 mC cm −2 , and the IrO x /ITO NW electrode exhibited a charge injection limit of 1.9 mC cm −2 and CSC utilization efficiency of approximately 45%. The stimulation performance of the IrO x /ITO NW electrode was confirmed using rat hippocampal slices, which exhibited a higher negative peak amplitude in the field excitatory postsynaptic potential when stimulated by a single pulse, and more effectively induced long-term potentiation via a theta burst stimulation compared with an ITO NW electrode. These results indicate that the synergetic combination of ITO NWs and a very thin IrO x layer enhanced the performance of the stimulus.

Flexible supercapacitor electrodes have been fabricated by simple fabrication technique using graphite nanoflakes on polymer lapping films as flexible substrate. An additional thin layer of conducting polymer polypyrrole over the electrode improved the surface conductivity and exhibited excellent electrochemical performances. Such capacitor films showed better energy density and power density with a maximum capacitance value of 37 mF cm(-2) in a half cell configuration using 1 M H2SO4 electrolyte, 23 mF cm(-2) in full cell, and 6 mF cm(-2) as planar cell configuration using poly(vinyl alcohol) (PVA)/phosphoric acid (H3PO4) solid state electrolyte. Moreover, the graphite nanoflakes/polypyrrole over polymer lapping film demonstrated good flexibility and cyclic stability.

In this paper we report the results on the optimization of the bi-layer lift-off resist (LOR) SiO2 sputter-deposition technique which is ideal for obtaining damage-free multi-electrode array (MEA). To optimize the bi-layer overhang formation, we have examined the undercut formation kinetics of LOR bottom layer and the dependence of the SiO2 sputter-deposition lift-off processed electrode structure on the undercut length. Crater-shaped and recessed electrode structure is obtained when the undercut length is short (≤2 μm) and longer than 3 μm, respectively. To optimize the SiO2 sputter-deposition process, we have examined the dependence of Au electrode passivation on the SiO2 sputtering parameters in terms of electrochemical cyclic-voltammogram (CV), impedance, electrical noise, sputter-deposition rate and in vitro neuronal activity recording property. The MEAs passivated under pure argon supply condition showed poor barrier properties, poor neuronal signal recording performance, and cytotoxic property. The CV of MEAs passivated under oxygen mixing ratios above 5% showed traditional sigmoidal CV and long-term recording of neuronal activities, probing the excellent barrier property and cytocompatibility of the SiO2 films sputter-deposited under oxygen mixing conditions. We have also issued thermal damaging aspect of bi-layer overhang structure which is tightly coupled with the detailed electrode structure and the high sputter-deposition rate. Finally, it was suggested that measurement of CV, electrochemical impedance and electrical noise can be a viable tool in evaluating the barrier performance of a passivation layer.

We covalently bound fluoropolymer (FP) films by plasma treatment followed by thermal pressing at temperatures below their melting point and fabricated an adhesion-metal-free flexible gold electrode array entirely encapsulated by the FP film, excepting the active electrode openings. The fabricated device was chemically resistant and was modified to have a lower impedance and efficient charge injection capability. The fabricated device was evaluated in vivo in rats and was confirmed to record the epidural epileptiform activity induced by chemical administration. The chemically inert nature of FPs and the gold electrode is expected to facilitate reliable neural interfacing without abiotic issues. Plasma treatment-induced covalent binding of FP films can also be utilized in a variety of applications requiring durability, such as implantable biosensors and sensor platforms operating under chemically harsh environments, including humid conditions.

In neural engineering studies, electrical stimulation feedback which is in response to measured neural activities from biological systems has important roles for mimicking artificial sensorymotor feedback paths and for controlling neural circuit plasticity. In previous works, a host PC in a closed-loop signal processing path resulted in uncontrollable milliseconds latency between a spike detection and an electrical stimulus. In this paper, we present an event-based delay-controlled stimulator controller with a priority queue in a real-time closed-loop bidirectional neural interface system. Event-based communication using an events table supports arbitrary feedback connections mapping to a biological system. Simplified event paths result in average 481.3 ns latency with few clock cycles jitter. In addition, axonal conduction delay is implemented using a priority queue with controllable jitter in a global timer temporal resolution. Precisely-controlled axonal conduction delay enables spatiotemporal pattern stimulation.

A multichannel neural interface system is an important tool for various types of neuroscientific studies. For the electrical interface with a biological system, high-precision high-speed data recording and various types of stimulation capability are required. In addition, real-time signal processing is an important feature in the implementation of a real-time closed-loop system without unwanted substantial delay for feedback stimulation. Online spike sorting, the process of assigning neural spikes to an identified group of neurons or clusters, is a necessary step to make a closed-loop path in real time, but massive memory-space requirements commonly limit hardware implementations. Here, we present a 128-channel field-programmable gate array (FPGA)-based real-time closed-loop bidirectional neural interface system. The system supports 128 channels for simultaneous signal recording and eight selectable channels for stimulation. A modular 64-channel analog front-end (AFE) provides scalability and a parameterized specification of the AFE supports the recording of various electrophysiological signal types with 1.59 ± 0.76 $\mu {V}$ root-mean-square noise. The stimulator supports both voltage-controlled and current-controlled arbitrarily shaped waveforms with the programmable amplitude and duration of pulse. An empirical algorithm for online real-time spike sorting is implemented in an FPGA. The spike-sorting is performed by template matching, and templates are created by an online real-time unsupervised learning process. A memory saving technique, called dynamic cache organizing, is proposed to reduce the memory requirement down to 6 kbit per channel and modular implementation improves the scalability for further extensions.

The interactions of anionic oxo-titanium (IV) meso -tetrakis(4-sulfonatophenyl)porphyrin and cationic oxo-titanium(IV) meso -tetrakis(1-methylpyridium-4-yl)porphyrin with anionic and cationic micelles were examined by Raman spectroscopy and transient absorption spectroscopy. The Raman bands of O Ti IV porphyrins in the presence of surfactants with same charge were similar to those observed in a pure water solution. The characteristic Raman band was observed at 915 cm −1 , which was assigned to the O Ti stretching mode of the 6-coordinated complex, O Ti (H 2 O) porphyrins. On the other hand, in the presence of oppositely charged surfactants, a markedly up-shifted Raman band was observed at 945 cm −1 , which was assigned to the O Ti stretching mode of a 5-coordinated complex, O Ti porphyrins. O Ti porphyrins interact with oppositely charged surfactant micelles by losing the sixth axial ligand (H 2 O). The 5-coordinate complexes showed a shorter lifetime of the exited triplet state due to the lower lying quenching state.

The photoreduction of water-soluble cationic manganese(III) meso-tetrakis(1-methylpyridium-4-yl)porphyrin (Mn(III)(TMPyP)(4+)) bound to a synthetic polynucleotide, either poly[d(A-T)2] or poly[d(G-C)2], was examined by conventional absorption and circular dichroism (CD) spectroscopy, transient absorption, and transient Raman spectroscopy. Upon binding, Mn(III)(TMPyP)(4+) produced a positive CD signal for both polynucleotides, suggesting external binding. In the poly[d(A-T)2]-Mn(III)(TMPyP)(4+) adduct case, an interaction between the bound porphyrin was suggested. The transient absorption spectral features of Mn(III)(TMPyP)(4+) in the presence of poly[d(A-T)2] and poly[d(G-C)2] were similar to those of the photoreduced products, Mn(II)(TMPyP)(4+), whereas Mn(III)(TMPyP)(4+) in the absence of polynucleotides retained its oxidation state. This indicated that both poly[d(A-T)2] and poly[d(G-C)2] act as electron donors, resulting in photo-oxidized G and A bases. The transient Raman bands (ν2 and ν4) that were assigned to porphyrin macrocycles exhibited a large downshift of ~25 cm(-1), indicating the photoreduction of Mn(III) to Mn(II) porphyrins when bound to both polynucleotides. The transient Raman bands for pyridine were enhanced significantly, suggesting that the rotation of peripheral groups for binding with polynucleotides is the major change in the geometry expected in the photoreduction process. These photoinduced changes do not appear to be affected by the binding mode of porphyrin.

A multielectrode array (MEA) was fabricated with electrodes consisting of iridium oxide (IrOx) electrochemically deposited on nanoporous gold (NPG) to improve the moderate charge injection limit (ca. 1 mC cm–2) of NPG MEA. IrOx was electrodeposited by performing cyclic voltammetry with an IrOx deposition solution. The IrOx was electrodeposited on Au (EIROF/Au) and on NPG (EIROF/NPG) MEA, and the samples were analyzed in terms of the charge injection limit, charge storage capacity (CSC), and electrochemical impedance. The charge injection limit of the EIROF(100-cycled)/NPG MEA was estimated to be 2.3 mC cm–2 by measuring the voltage transient, and this value is sufficiently greater than the neural damage threshold (ca. 1 mC cm–2) and is also comparable to that of sputtered IrOx films. Considering the low charge injection limit (

We have synthesized photocrosslinkable benzophenone copolymer, Poly(St- co -MBz), and fabricated cell-repellent patterns of Poly(St- co -MBz) on covalently bound poly- d -lysine (PDL) layer via the photocrosslinking. We have successfully obtained fine grid line pattern with line width of 3 μm and fine neurite, presumably axon, patterns with excellent pattern fidelity. We found that benzophenone unit can be crosslinked under the exposure of UV (with the intensity of ∼77 mW/cm 2 at 280 nm and ∼60 mW/cm 2 at 365 nm) without photo-oxidative damage to PDL, poly- l -lysine, and polyethyleneimine.

We present herein a simple protocol of growing a patterned ZnO nanowire by etching of ZnO seed layer in the tetramethyl ammonium hydroxide (TMAH) solution. The ZnO seed layer was fabricated by sol–gel method using zinc acetate solution and patterned by using photolithographic method. Patterned ZnO seed layer as etched in the TMAH solution, followed by growth of ZnO nanowires by hydrothermal method. Remarkable point of present ZnO seed layer patterning is that development of UV-exposed photoresist and etching of ZnO seed layer is subsequently processed in aqueous TMAH solution without interruption. The grown ZnO nanowires were analyzed using XRD patterns to exhibit high purity and degree of crystallinity, and showed very good pattern fidelity.

We have prepared the poly-d-lysine (PDL) bound surfaces for neuron cell culture by covalent binding between the poly-d-Lysine and substrates and investigated neuronal cell adhesion properties and cell growth morphology. The number of neuronal cell and the number of neurite per neuronal cell on PDL bound surfaces was much more than those on PDL coated surfaces and also the neuronal cells on PDL bounded surfaces survived a longer time. On the pattern of covalently bound PDL, neuronal cells and their neurites are confined within the grid line leading to patterned neuronal networks with the long-term survival.

The molecular association of acceptors with electron donors is studied in the highly-polar solvent CH3CN. Tetracyanoquinodimethane (TCNQ) forms a stable charge-transfer complex with donor molecules such as 4aminobiphenyl (4-AB), benzidine (BD) and 2-aminobiphenyl (2-AB) with high association constants. The complexes of TCNQ with 4-AB or BD show new absorption bands at around 800 and 500 nm, which can be identified as reduced TCNQ − and TCNQ 2− species, respectively. These bands grow quickly upon photoirradiation, implying that the charge-transfer complexes are easily formed in an excited state. Conversely, a small spectral manifestation of the charge transfer was observed in the case of 2-AB complex. It is demonstrated that the structural orientation between the geminate ion pairs could play an important role in building a stable complex.

Microelectrode for neural signal recording was modified with Au-Pt nanoparticles (NPs). Impedance of Au-Pt NP-modified electrode was decreased by one order of magnitude compared with bare gold electrode which results in decreasing baseline noise and higher signal to noise than those of the Au NP-modified MEA. The reasonable neuron cell viability and spike recording capability were observed on Au-Pt NPs- modified electrode.

In the optical drive system adopting optical flying-type head (OFH), flying stability of small OFH interfaced with a removable plastic disk is investigated as basic functions of reliable optical pickup head for first surface recording. Additional micro actuators for focus servo are studied for better interface of OFH on the thin cover layered plastic disk to eliminate focus error due to the non-uniformity in cover layer thickness and the tolerance of lens assembly.

We performed nonlinear transmission measurements and quantum-chemical calculations on dithienothiophene (DTT)-based molecules to gain insight into the effect of acceptor and donor groups on two-photon absorption (TPA) properties. The TPA intensity showed dispersion characteristics of the single-photon absorption spectrum. When the molecules included an asymmetric donor-acceptor pair, the single- and two-photon absorption maximum wavelengths were red-shifted more than when the molecules had a symmetric donor-donor structure. We interpreted this result as indicating that the S 2 state plays the dominating role in the absorption process of molecules with a symmetric structure. The experimental TPA δ values at the absorption peak wavelength showed a dependence on the structural variations. We found the self-consistent force-field theory and Hartree-Fock Hamiltonian with single configuration interaction formalism to be valid for evaluating TPA δ. Although the quantum-chemical calculations slightly underestimated the experimental 8 values obtained from nonlinear transmission measurements, they reasonably predicted the dependence of the 8 value on the structural variations. We confirmed the role of molecular symmetry by observing that donor-donor substituted structure gave the highest experimental and theoretical TPA 8 values and that the donor-acceptor substituted structure showed a greater redshift in the TPA absorption maximum wavelength. Overall, the theoretical 8 values of DTT-based molecules were in the order of 10 -46 cm 4 .s.photon -1 and are higher than that of AF-50 by nearly two orders of magnitude.

We have calculated TPA cross section Δ value of dithienothiophene (DDT)-based molecules to gain insight into the origin of the large δ values. The energy and transition dipole moments for the ground state and multiple excited states were calculated by combining the Hartree-Fock Hamiltonian with single configuration interaction formalism. For the calculation of the imaginary part of the third-order polarizability the sum-over-state expression was used. There are some differences between theoretical and experimental values. However the theoretical calculation reasonably estimates the δ values of the DTT-based molecules roughly 2–10 times larger than those fluorene- as well as stilbene-based ones.

High two-photon absorption (TPA) molecule having a fluorene π-center (TP-Flu-TP) was prepared by the Heck reaction of 2,7-dibromo-9,9-diethylhexyl-9H-fluorene and 4-(diphenylamino)benzstyrene. The linear absorption maximum of the TP-Flu-TP was observed at 410 nm. The dispersion of the TPA intensity for the chromophore was measured by nonlinear transmission using 7 ns laser pulse. Since the maximum wavelength of this molecule occurred at 740 nm, we fixed the pumping wavelength at 740 nm for TP-Flu-TP and measured the transmitted pulse energy versus the input pulse energy. From this experiment we observed a distinct nonlinearity from TP-Flu-TP demonstrating that it is a potential material for optical limiting. The calculated two-photon absorption cross section (Δ) by the Hartree-Fock Hamiltonian with single configuration interaction formalism was 1.37 × 10−47 cm4 sec/photon.

We have fabricated spin valve ring shape sensors for the detection of micrometer size magnetic beads. By using a ring shape spin valve sensors, we were able to detect the presence of 2.8 mum size magnetic beads by direct measurement of magnetic dipole fields from the magnetic beads. The abrupt transition position of ring sensor transfer curves was changed from the 5 Oe to -10 Oe due to the presence of the 12 magnetic beads. It was also found that the sensitivities of ring sensors without and with magnetic beads were obtained about 0.11 mV/Oe and 0.08 mV/Oe, respectively. Variations of the abrupt transition position and maximum output signal were explained by the magnetic bead stray field effect. Our results shows that ring shape spin valve magnetic sensors are promising for the detection of biomolecules with magnetic labels.

(Ba, Sr)TiO3(BST) thin films were prepared by pulsed laser deposition on the perovskite conductive oxide LaNiO3 (LNO), YBa2Cu3O7−δ(YBCO) films, and Pt as a bottom electrode. The crystalline structures and surface microstructrue of the BST deposited on several substrates were characterized by x-ray diffraction measurement and scanning electron microscopy, respectively. The electrode effects on low-frequency dielectric behavior of BST thin films were investigated. The complex dielectric constants of the films were measured as a function of frequency in the frequency range from 0.1 Hz to 10 MHz. BST films grown on metallic oxide substrates exhibited marked dielectric relaxation below 10 MHz. This low frequency dielectric relaxations is attributed to the ionized space charge carriers such as the oxygen vacancies and cation defects in BST film, and the interfacial polarization in the grain boundary region and the electrode/film interface.

Light-emitting properties of a solvent processable poly(1,4-phenylenevinylene) (PPV) derivative, poly[2-bis(dimethyloctylsilyl)-1,4-phenylenevinylene] (BDMOS-PPV) have been studied Synthesized BDMOS-PPV is highly fluorescent and the measured absolute PL quantum efficiency is exceeding 60%. Single layer electroluminescent device (ITO/BDMOS-PPV/Al) exhibits an emission maximum at 515 nm which corresponds to the green region.

The electroluminescent characteristics of polymer/organic heterostructured device that fabricated with poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and tris(8-hydroxyquinoline) aluminum (Alq3) is studied. The electroluminescent property of MEH-PPV/Alq3 device shows high luminescence with small current flow. The low molecular weight organic film that is formed on the emissive polymer acts as a hole blocking layer. The current limited structure of polymer/organic electroluminescent device is suggested and discussed to reduce the effect of Joule heat caused by the large current flow.

We report on the investigations of electroluminescence (EL) for the polymer blend composed of two organic soluble polymers. The blends consist of main chain conjugated poly[(2-methoxy-5-((2-ethylhexyl)oxy)-1,4-phenylene)vinylene] (MEH−PPV) and a side chain luminescent polymer, an alkoxy(trifluoromethyl)stilbene-substituted PMA derivative (CF3−PMA). Emitting colors of the polymer blends varied with the blending ratios of two polymers. The electroluminescent peak of the MEH−PPV-rich polymer blend ranged over 580−800 nm (orange-red light), and of the CF3−PMA-rich polymer blend ranged from 380 to 800 nm, resulting in a white-light emission. Additional new EL peaks of polymer blends at around 380 and 800 nm would originate from the CF3−PMA and the exciplex formed by photoinduced electron transfer between two polymers.

Highly quantum efficient and multi-color emissible polymer light emitting devices have been realized utilizing poly (1-dodecyloxy-4-methyl-1, 3-phenylene)(2, 5"-terthienylene)(hereafter, mPTTh polymer) as an emitting layer and tris(8-hydroxyquinoline) aluminum (Alq3) as an electron transport layer. A single layer EL device of mPTTh polymer emits orange-colored light. EL efficiency increases as the thickness of Alq3 layer increases, but the emission color becomes visually broad when the Alq3 layer thickness is greater than 30nm since the relative peak intensity of green EL from Alq3 layer grows. EL color is changed from orange to greenish orange as the thickness of Alq3 layer grows. EL color is changed from orange to greenish orange as the thickness of Alq3 layer increases. EL efficiency of the double layer device was greatly enhanced by 3000 times compared with that of a single layer device. Alq3 layer in device acts as a hole blocking electron transporting layer and an emitting layer as a function of the thickness of Alq3 layer.ayer.

We report the observations of electroluminescence of photodegraded poly(p-phenylenevinylene) derivatives film which was irradiated with laser light at a wavelength in the region of ultraviolet. EL spectral change for different polymers shows different behaviour. Electroluminescence and photoluminescence intensities of PPV decreases rapidly and the intensities in the blue region become relatively severe without peak shift. MEH-PPV shows the blue shift of the peak in EL spectra with negligible intensity decrement. Spectroscopic results of the PPV film degraded by UV light support the photodegradation occurred by chain-scission process.

Electrochemical deposition of gold nanoparticles (Au NPs) on the gold multi-electrode array (MEA) fabricated with bi-layer lift-off resist sputter-deposition technique was performed. Electrochemical deposition was performed by potentiostatic and cyclic voltammetry method. The surface of Au NP-modified electrode showed various morphologies with applied voltage and the concentration of HAuCl4 solution. The Au NP-modified electrode was characterized by electrochemical impedance spectroscopy and cyclic voltammogram. The performance of Au NP-modified MEA was also tested by neuronal signal recording. The Au NP-modified MEA exhibited lower baseline noises and can record neuronal spike signals longer than the bare Au MEA.

In order to provide high quality visual information to patients who have implanted retinal prosthetic devices, the number of microelectrode should be large. As the number of microelectrode is increased, the dimension of the microelectrode is decreased, which in turn results in the increased interface impedance of microelectrode and decreased dynamic range of injection current. In addition, the reduced maximum limit of injection current may not be sufficiently large to stimulate the ganglion cells in a retina. In order to improve the trade-off envelope between number of microelectrode and current injection limit, a 3D microelectrode structure can be used as an alternative. From the advancement of microfabrication technology, the fabrication of highly-accurate 3D structures with small dimensions is possible. This paper presents a first comprehensive electrical characterization of 2D and 3D microelectrodes for high-resolution retinal prostheses. Microelectrodes which differ in shapes and diameters are analyzed. Their interface impedances and charge injection limits are quantitatively analyzed. This research can be used to define requirements for further retinal prosthetic device research.

Molecular conformations of stereoregular poly(methyl methacrylate) (PMMA) monolayers have been investigated by scanning probe microscopes. Isotactic and syndiotactic PMMAs were found to have right and left hand helical structures, respectively. On the contrary atactic PMMA showed rather random arrangement of the chains. It has been demonstrated that the PMMA Langmuir-Blodgett (LB) films can be utilized to form nanoscale patterns down to 50 nm and to form a geodesic lens. It has also been manifested that the quantum efficiency of a polymer electroluminescent device can be significantly enhanced by inserting the PMMA LB films between the emitting layer and the cathode. All the applications utilize the unique characteristics of the LB films to form thin and uniform films in the molecular level.

A blue light emitting device has been successfully fabricated using a polymer with regulated conjugation length containing trimethylsilyl substituted phenylenevinylene units. Electroluminescence from the device has an emission maximum at 470 nm. The device shows typical diode characteristics with operating voltage of 20 V and the light becomes visible at a current density of less than 0.5 mA/cm 2 . The electroluminescence spectrum is virtually identical with the photoluminescence spectrum, indicating that the radiation mechanisms are the same for both. A light emitting device using the blend of a large band gap polymer and a small band gap polymer was also fabricated. Light emission from the small band gap polymer shows much improved quantum efficiency, but there is no light emission from the large band gap polymer. Quantum efficiency of the blend increases up to about two orders of magnitude greater than that of the small band gap polymer with increasing proportion of the large band gap polymer. The improvement in quantum efficiency is interpreted in terms of exciton transfer and the hole blocking behaviour of the large band gap polymer. Finally, we have fabricated a patterned flexible light emitting device using the high quantum efficiency polymer blend system.

A 1 × N polymeric space switch using the thermo-optic effect in a planar waveguide which can be controlled by just one electric control line was demonstrated by employing a specially designed stripe heater which consists of N − 1 straight sections of different widths connected with proper angle.

The molecular configuration of isotactic PMMA Langmuir-Blodgett (LB) films was investigated with scanning tunnelling microscopy (STM). STM images of the isotactic PMMA LB films, transferred at the surface pressure of 15 mN m −1 , show a closely packed well-ordered arrangement in which two phases with helical and linear chain configurations are mixed. The appearance of the STM images and the width and pitch of the helix indicate that the transition at the surface pressure of 8 mN m −1 corresponds to formation of the right-handed 5 1 single-strand helix. The transformation process can be explained by a one-dimensional growth.

We have developed a novel platform for selective binding of magnetic labels on planar Hall resistance sensor (PHR) for biosensing applications. The photoresist (PR) micro wells were prepared on the PHR sensor junctions to trap the magnetic bead at specified locations on the sensor surface and thin layer of Au was sputtered in the PR wells immobilize bimolecular. The Au surface is functionalized with single-stranded oligonucleotide and further biotin was used to immobilize streptavidin coated magnetic labels (Dynabeads Myone 1.0 microm, Invitrogen Co.). After removal of the PR wells on the sensor surface the non specific binding magnetic labels were successfully removed and only the chemically bounded magnetic labels were remained on the Au surface for detection of biomolecules using PHR sensor. We controlled the number of magnetic labels on the PHR sensor surface by using different sizes of the PR well on the junctions. The specifically bounded magnetic labels were successfully detected by characterizing the individual PHR sensor junctions. This technique enables the complete control over the magnetic labels for selective binding of biomolecules on the sensor surface for increasing the sensitivity of the PHR sensor as well as removal of the non specific bindings on the sensor surface.

We describe photopatterning technique that employs the photodegradation of cell-adhesive-modified poly(ethyleneimine) (m-PEI) to fabricate precise micropatterns on the indium tin oxide (ITO) substrate for guided neuronal growth. The photodegradation of m-PEI coated on hydroxyl group-terminated ITO substrate created micropatterns over a large area through deep UV irradiation. The photopatterned m-PEI layer can effectively guide neurite outgrowth and control neurite extensions from individual neurons.

We investigate the effects of the thermal annealing on the performance of the ITO/electroluminescent polymer/electron transport layer/Al device. We observe the enhancement in light output and stability compared with the non-thermal treated device. We discuss the effects of step-by-step thermal treatment of the interfaces on the electroluminescent characteristics.

The fluorescence emission properties of 2-(2'-hydroxy-4'-R-phenyl)benzothiazole (HBT-R) nanoparticles with different substituents (R = -COOH, -H, -CH(3), -OH, and -OCH(3)) were investigated using spectroscopic and theoretical methods. HBT-Rs displayed dual enol and keto (excited-state intramolecular proton transfer (ESIPT)) emissions in nonpolar solvents. The spectral change of their ESIPT emissions was affected differently by the electron donating (or withdrawing) power of the substituents; a bathochromic shift for the electron donating group and a hypsochromic shift in electron withdrawing group. In addition, the changes in energy levels calculated by the ab initio method were consistent with the spectral shifts of HBT-R in solution. We prepared aggregated HBT-R nanoparticles using a simple reprecipitation process in tetrahydrofuran-water solvents. The ESIPT emission of aggregated HBT-R nanoparticles was strongly enhanced (over 45 times) compared to those of monomer HBT-Rs in toluene, as markedly shifted ESIPT emissions are observed at longer wavelength without any quenching by self-absorption. Aggregated HBT-R nanoparticles showed longer lifetimes than those of monomer molecules. The temperature effect on the aqueous dispersion of the aggregated HBT-R nanoparticles was also explored. It shows a fluorescent ratiometric change in a range of temperature from 7 to 65 degrees C. A mechanism of a temperature-dependent equilibrium between the nanoparticles and the solvated enols is proposed for the emission color change.

We have discovered that the sulfonation of polystyrene can form a gradient-index medium useful for lightfocusing purposes. We found that the refractive index of sulfonated polystyrene varies with the degree of sulfonation and that the refractive index of the fully sulfonated polystyrene decreased by approximately 0.06 at 0.633 microm from that of pure polystyrene.

In order to improve the efficiency of infection of primary human endothelial cells in vitro of Kaposi's sarcoma-associated herpesvirus (KSHV), the effect of low speed centrifugation was investigated. The recombinant KSHV, BAC36, was used to examine the centrifugal enhancement of KSHV. Infectivity was estimated by green fluorescent protein (GFP) expression and real-time RT-PCR. The enhancement of infectivity was dependent upon the time and force of centrifugation in human umbilical vein endothelial cells (HUVECs). Centrifugation enhanced the infectivity of KSHV by up to 70 fold compared to non-centrifugal control infection for the same period of time; viral mRNA expression was also enhanced by centrifugation. HUVECs that were centrifuged before infection with KSHV displayed no enhancement in infectivity; therefore, enhancement is believed to occur during centrifugation. In addition, the mechanisms of infection including the initial viral attachment to cells, lipid rafts, and clathrin-mediated and caveolae endocytosis appear to be similar in KSHV infection with and without centrifugal enhancement. These results show that low speed centrifugation could be a useful tool for improving the efficiency of KSHV infection in vitro.

Objective. Nanoporous gold (Au) structures can reduce the impedance and enhance the charge injection capability of multi-electrode arrays (MEAs) used for interfacing neuronal networks. Even though there are various nanoporous Au preparation techniques, fabrication of MEA based on low-cost electro-codeposition of Ag:Au has not been performed. In this work, we have modified a Au MEA via the electro-codeposition of Ag:Au alloy, followed by the chemical etching of Ag, and report on the in vitro extracellular recording and stimulation performance of the nanoporous Au-modified MEA. Approach. Ag:Au alloy was electro-codeposited on a bilayer lift-off resist sputter-deposition passivated Au MEA followed by chemical etching of Ag to form a porous Au structure. Main results. The porous Au structure was analyzed by scanning electron microscopy and tunneling electron microscopy and found to have an interconnected nanoporous Au structure. The impedance value of the nanoporous Au-modified MEA is 15.4 ± 0.55 kΩ at 1 kHz, accompanied by the base noise V rms of 2.4 ± 0.3 μV. The charge injection limit of the nanoporous Au-modified electrode estimated from voltage transient measurement is approximately 1 mC cm−2, which is comparable to roughened platinum and carbon nanotube electrodes. The charge injection capability of the nanoporous Au-modified MEA was confirmed by observing stimulus-induced spikes at above 0.2 V. The nanoporous Au-modified MEA showed mechanical durability upon ultrasonic treatment for up to an hour. Significance. Electro-codeposition of Ag:Au alloy combined with chemical etching Ag is a low-cost process for fabricating nanoporous Au-modified MEA suitable for establishing the stimulus–response relationship of cultured neuronal networks.

In this work, Cath.a-differentiated (CAD) cells were used in place of primary neuronal cells to assess the performance of vertically aligned carbon nanotubes (VACNTs) multi-electrode arrays (MEA). To fabricate high-performance MEA, VACNTs were directly grown on graphene/Pt electrodes via plasma enhanced chemical deposition technique. Here, graphene served as an intermediate layer lowering contact resistance between VACNTs and Pt electrode. In order to lower the electrode impedance and to enhance the cell adhesion, VACNTs-MEAs were treated with UV-ozone for 20 min. Impedance of VACNTs electrode at 1 kHz frequency exhibits a reasonable value (110 kΩ) for extracellular signal recording, and the signal to noise ratio the is good enough to measure low signal amplitude (15.7). Spontaneous firing events from CAD cells were successfully measured with VACNTs MEAs that were also found to be surprisingly robust toward the biological interactions.

We report on the investigation of electroluminescence (EL) for a dye-doped polymer. This doping system consists of main chain conjugated poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and highly fluorescent dye rubrene. We fabricated many EL samples of various doping ratios due to the good solubility of rubrene and MEH-PPV in organic solvents. Low operation voltage and high EL efficiency were obtained simultaneously in the molecularly doped system. We made EL cells having an emission efficiency 10 times higher than that of an undoped MEH-PPV diode with nearly the same turn-on voltage.

Transfer characteristics of polymethacrlylate Langmuir films with various side chains have been investigated at different values of transfer surface pressure. Surface pressure-area (π-A) isotherms and surface potentials of polymethacrylate with various side chains were measured and apparent dipole moments of these Langmuir films at the air-water interface were calculated by using π-A isotherms and surface potentials measured. Transfer characteristics of polymethacrylate Langmuir films with different side chains were discussed in terms of the interactions between the films and the subphase and also the internal cohesions of polymethacrylate monolayers.

Very recently, Chittibabu et al. (1996) have successfully synthesized a polythiophene containing a methane side chain, poly[2-(3-thienyl) ethanol n-butoxy carbonylmethyl methane] (PURET), in order to improve the solubility. In this paper a single-layered light-emitting device structure was fabricated by spin-coating the PURET dissolved in strong polar solvent onto an indium-tin oxide (ITO) coated glass. Photoluminescence and electroluminescence spectra of the device were measured.