PEDOT–CNT Composite Microelectrodes for Recording and Electrostimulation Applications: Fabrication, Morphology, and Electrical Properties

Composites of carbon nanotubes and poly(3,4-ethylenedioxythiophene, PEDOT) and layers of PEDOT are deposited onto microelectrodes by electropolymerization of ethylenedioxythiophene in the presence of a suspension of carbon nanotubes and polystyrene sulfonate. Analysis by FIB and SEM demonstrates that CNT–PEDOT composites exhibit a porous morphology whereas PEDOT layers are more compact. Accordingly, capacitance and charge injection capacity of the composite material exceed those of pure PEDOT layers. In vitro cell culture experiments reveal excellent biocompatibility and adhesion of both PEDOT and PEDOT–CNT electrodes. Signals recorded from heart muscle cells demonstrate the high S/N ratio achievable with these electrodes. Long-term pulsing experiments confirm stability of charge injection capacity. In conclusion, a robust fabrication procedure for composite PEDOT–CNT electrodes is demonstrated and results show that these electrodes are well suited for stimulation and recording in cardiac and neurophysiological research

Adressierbarer Biochip zur elektrophoretischen Anreicherung geladener Biomoleküle

Adressierbare Biochip-Arrays ermöglichen die räumliche Manipulation geladener Biomoleküle durch Elektrophorese. Durch Akkumulation bestimmter Moleküle bzw. Auftrennung von Gemischen im elektrischen Feld soll die Sensitivität und die Selektivität nachgeschalteter bioanalytischer Verfahren gesteigert und die für eine Analyse erforderliche Probenmenge verringert werden. Das addressierbare Biochip-Array wird mit Methoden der Dünnschicht- und Mikrostrukturtechnik Probenvolumen. Auf dem Chip sind Fokussierungselektroden integriert. Sie erzeugen in der über dem Chip liegenden, elektrolytgefüllten Kammer ein zum zentral angeordneten Mikroelektrodenarray gerichtetes elektrisches Feld. Die präzise kontrollierte Ansteuerung der Fokussierungselektroden mit konstanter Stromdichte ist besonders wichtig, um störende Gasentwicklung zu vermeiden. Auf den Mikroelektroden werden Moleküle angesammelt und stehen für eine Analyse durch Fluoreszenzmessung oder mittels elektrischer Nachweisverfahren zur Verfügung. Die Akkumulation von DNA-Oligomeren, Protein und Peptiden um einen Faktor von bis zu 200 wurde bereits demonstriert. Das Verfahren soll zur Probenkonditionierung in Lab-on-a-chip Systemen oder als aktives Substrat für Proteomicsanwendungen eingesetzt werden

Recent Developments in Fluorescence Correlation Spectroscopy for Diffusion Measurements in Planar Lipid Membranes

Fluorescence correlation spectroscopy (FCS) is a single molecule technique used mainly for determination of mobility and local concentration of molecules. This review describes the specific problems of FCS in planar systems and reviews the state of the art experimental approaches such as 2-focus, Z-scan or scanning FCS, which overcome most of the artefacts and limitations of standard FCS. We focus on diffusion measurements of lipids and proteins in planar lipid membranes and review the contributions of FCS to elucidating membrane dynamics and the factors influencing it, such as membrane composition, ionic strength, presence of membrane proteins or frictional coupling with solid support

SENSITIVE DETECTION OF PROTEIN ADSORPTION TO SUPPORTEDLIPID BILAYERS BY CAPACITANCE MEASUREMENTS

Wereport experiments on the sensitive detection of protein adsorption to lipid bilayers deposited onto chromium electrodes on glass substrates by capacitance measurements. The sensitivity of the present type of sensor (better than 3A average protein layer thickness) is at least equivalent to that of ellipsometry. A high specific resistance of the supported bilayer of (1-5)-10%cm® is achieved by deposition of a tightly packed (crystalline) cadmium arachidate monolayer in contact with the substrate, whereas the outer monolayer can be more loosely packed (fluid phase or state of fluid-solid coexistence) which is essential for the incorporation of receptors. In the present work, charged lipids are incorporated as nonspecific receptors for polylysine and cytochrome c. Furthermore, the capacitance measurements provide a very sensitive test for the tightness and long-time stability of supported bilayers

Can Nanofluidic Chemical Release Enable Fast, High Resolution Neurotransmitter-Based Neurostimulation?

Artificial chemical stimulation could provide improvements over electrical neurostimulation. Physiological neurotransmission between neurons relies on the nanoscale release and propagation of specific chemical signals to spatially-localized receptors. Current knowledge of nanoscale fluid dynamics and nanofluidic technology allows us to envision artificial mechanisms to achieve fast, high resolution neurotransmitter release. Substantial technological development is required to reach this goal. Nanofluidic technology — rather than microfluidic — will be necessary; this should come as no surprise given the nanofluidic nature of neurotransmission.This perspective reviews the state of the art of high resolution electrical neuroprostheses and their anticipated limitations. Chemical release rates from nanopores are compared to rates achieved at synapses and with iontophoresis. A review of microfluidic technology justifies the analysis that microfluidic control of chemical release would be insufficient. Novel nanofluidic mechanisms are discussed, and we propose that hydrophobic gating may allow control of chemical release suitable for mimicking neurotransmission. The limited understanding of hydrophobic gating in artificial nanopores and the challenges of fabrication and large-scale integration of nanofluidic components are emphasized. Development of suitable nanofluidic technology will require dedicated, long-term efforts over many years