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.
This review aims at providing an introductory overview for researchers new to the field of ion-selective electrodes. Both state of the art technology and novel developments towards solid-contact reference (sc-RE) and solid-contact ion selective electrodes (sc-ISE) are discussed. This technology has potentially widespread and important applications provided certain performance criteria can be met. We present basic concepts, operation principles, and theoretical considerations with regard to their function. Analytical performance and suitability of sc-RE and sc-ISE for a given application depend on critical parameters, which are discussed in this review. Comprehensive evaluation of sensor performance along this set of parameters is considered indispensable to allow for a well-founded comparison of different technologies. Methods and materials employed in the construction of sc-RE and sc-ISE, in particular the solid contact and the polymer membrane composite, are presented and discussed in detail. Operation principles beyond potentiometry are mentioned, which would further extend the field of ISE application. Finally, we conclude by directing the reader to important areas for further scientific research and development work considered particularly critical and promising for advancing this field in sensor R&D. Graphical Abstract ᅟ.
A facile method is proposed for the deposition of multiwalled carbon nanotube (MWCNT) layers onto microelectrode arrays by means of a microcontact printing technique, leading to the fabrication of MEAs characterized by well defined electrical and morphological properties. Using polydimethyl siloxane stamps, produced from different mold designs, a flexibility of printing is achieved that provides access to microscale, nanostructured electrodes. The thickness of MWCNT layers can be exactly predetermined by evaluating the concentration of the MWCNT solution employed in the process. The electrode morphology is further characterized using laser scanning and scanning electron microscopy. Next, by means of impedance spectroscopy analysis, the MWCNT-electrode contact resistance and MWCNT film resistance is measured, while electrochemical impedance spectroscopy is used to estimate the obtained electrode-electrolyte interface. Structural and electrochemical properties make these electrodes suitable for electrical stimulation and recording of neurons and electrochemical detection of dopamine. MWCNT-functionalized electrodes show the ability to detect micromolar amounts of dopamine with a sensitivity of 19 nA μm(-1) . In combination with their biosensing properties, preliminary electrophysiological measurements show that MWCNT microelectrodes have recording properties superior to those of commercial TiN microelectrodes when detecting neuronal electrical activity under long-term cell-culture conditions. MWCNT-functionalized microelectrode arrays fabricated by microcontact printing represent a versatile and multipurpose platform for cell-culture monitoring.
We have developed a microfluidic system--microPrep--for subcellular fractionation of cell homogenates based on dielectrophoretic sorting. Separation of mitochondria isolated from a human lymphoblastoid cell line was monitored by fluorescence microscopy and further characterized by western blot analysis. Robust high throughput and continuous long-term operation for up to 60 h of the microPrep chip system with complex biological samples became feasible as a result of a comprehensive set of technical measures: (i) coating of the inner surfaces of the chip with BSA, (ii) application of mechanical actuators to induce periodic flow patterns, (iii) efficient cooling of the device to ensure integrity of organelle, (iv) a wide channel to provide for high fluidic throughput, and (v) integration of a serial arrangement of 10 dielectrophoretic deflector units to enable separation of samples with a high particle load without clogging. Hence, microPrep yields tens of micrograms of enriched and purified mitochondria within hours. Western blots of mitochondria fractions showed that contaminating endoplasmatic reticulum was reduced by a factor 6 when compared with samples prepared by state of the art centrifugation.
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