Photorelease of caged Ca(2+) is a uniquely powerful tool to study the dynamics of Ca(2+)-triggered exocytosis from individual cells. Using photolithography and other microfabrication techniques, we have developed transparent microchip devices to enable photorelease of caged Ca(2+), together with electrochemical detection of quantal catecholamine secretion from individual cells or cell arrays as a step towards developing high-throughput experimental devices. A 100 nm thick transparent indium-tin-oxide (ITO) film was sputter-deposited onto glass coverslips, which were then patterned into 24 cell-sized working electrodes (approximately 20 microm by 20 microm). We loaded bovine chromaffin cells with acetoxymethyl (AM) ester derivatives of the Ca(2+) cage NP-EGTA and Ca(2+) indicator dye fura-4F, then transferred these cells onto the working ITO electrodes for amperometric recordings. Upon flash photorelease of caged Ca(2+), a uniform rise of [Ca(2+)](i) within the target cell leads to quantal release of oxidizable catecholamines measured amperometrically by the underlying ITO electrode. We observed a burst of amperometric spikes upon rapid elevation of [Ca(2+)](i) and a "priming" effect of sub-stimulatory [Ca(2+)](i) on the response of cells to subsequent [Ca(2+)](i) elevation, similar to previous reports using different techniques. We conclude that UV photolysis of caged Ca(2+) is a suitable stimulation technique for higher-throughput studies of Ca(2+)-dependent exocytosis on transparent electrochemical microelectrode arrays.

Neurons and endocrine cells secrete neurotransmitter and hormones in discrete packets in a process called quantal exocytosis. Electrochemical microelectrodes can detect spikes in current resulting from the oxidation of individual quanta of transmitter only if the electrodes are small and directly adjacent to release sites on the cell. Here we report development of a microchip device that uses microfluidic traps to automatically target individual or small groups of cells to small electrochemical electrodes. Microfluidic channels and traps were fabricated by multi-step wet etch of a silicon wafer whereas Pt electrodes were patterned in register with the trap sites. We demonstrate high-resolution amperometric measurement of quantal exocytosis of catecholamines from chromaffin cells on the device. This reusable device is a step towards developing high-throughput lab-on-a-chip instruments for recording quantal exocytosis to increase the pace of basic neuroscience research and to enable screening of drugs that target exocytosis.

Carbon electrodes are widely used in electrochemistry due to their low cost, wide potential window, and low and stable background noise. Carbon-fiber electrodes (CFE) are commonly used to electrochemically measure "quantal" catecholamine release via exocytosis from individual cells, but it is difficult to integrate CFEs into lab-on-a-chip devices. Here we report the development of nitrogen doped diamond-like carbon (DLC:N) microelectrodes on a chip to monitor quantal release of catecholamines from cells. Advantages of DLC:N microelectrodes are that they are batch producible at low cost, and are harder and more durable than graphite films. The DLC:N microelectrodes were prepared by a magnetron sputtering process with nitrogen doping. The 30 μm by 40 μm DLC:N microelectrodes were patterned onto microscope glass slides by photolithography and lift-off technology. The properties of the DLC:N microelectrodes were characterized by AFM, Raman spectroscopy and cyclic voltammetry. Quantal catecholamine release was recorded amperometrically from bovine adrenal chromaffin cells on the DLC:N microelectrodes. Amperometric spikes due to quantal release of catecholamines were similar in amplitude and area as those recorded using CFEs and the background current and noise levels of microchip DLC:N electrodes were also comparable to CFEs. Therefore, DLC:N microelectrodes are suitable for microchip-based high-throughput measurement of quantal exocytosis with applications in basic research, drug discovery and cell-based biosensors.

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Crystallization of amorphous silicon ͑a-Si͒ thin film occurred by the self-propagation of copper oxide/aluminum thermite nanocomposites. Amorphous Si films were prepared on glass at a temperature of 250°C by plasma enhanced chemical vapor deposition. The platinum heater was patterned on the edge of the substrate and the CuO / Al nanoengineered thermite was spin coated on the substrate that connects the heater and the a-Si film. A voltage source was used to ignite the thermites followed by a piranha solution ͑4 Unlike most other techniques, laser induced crystallization does not require high temperatures ͑Ͼ180°C͒ and long processing times to produce good quality poly-Si films. The major disadvantage of laser crystallization is its low throughput due to small laser spot size, which is not suitable for large area such as solar cells. Thus, high temperature and long processing times for various crystallization methods, and small spot size of the laser are not suitable for producing poly-Si film on a large surface area of glass or flexible plastic substrates. Low cost plastic substrates such as polyethersulphone can be used for flexible electronics if the device is fabricated under 180°C. This study investigates the crystallization of a-Si layer achieved by the ignition of nanoengineered thermite materials such as CuO / Al. Explosives have been utilized previously to crystallize amorphous materials; 5,6 however, there is no information currently available on thin film crystallization using nanoengineered thermites. Our approach utilizes thermite reaction to induce crystallization of a-Si thin film; such energetic reactions are self-propagating exothermic reactions, which produce localized heating effects. We discovered that thermites, nanoengineered by the self-assembly approach, produced a self-propagating chemical reaction over a period of microseconds. 7,8 The exothermic reaction propagates at a rate of 1500-2000 m / s resulting in heat release. This heat can be used advantageously to crystallize a-Si. High quality poly-Si films can be prepared on large substrates utilizing this released heat. Nanoengineered thermites were prepared by sonicating a mixture of CuO nanorods ͑10 nm diameter and 70 nm long͒ and aluminum nanopowder ͑80 nm diameter͒. The details of the nanorod preparation and the characterization of the thermites are presented in Ref. 9. The thermites displayed the following chemical reaction:where ⌬H is the released heat. For CuO / Al exothermic reaction, the released heat is 604 kJ/ mol and the adiabatic reaction temperature is 3794 K. 10The a-Si samples were prepared by plasma enhanced chemical vapor deposition on glass substrates. The thickness of the a-Si layer was 300 nm. A thin layer of platinum ͑90 nm thick and 2.5 mm wide͒ was deposited on the edge of the substrates, which functioned as a heater for initiating the self-propagating reaction for the energetic materials. The substrates with a-Si and the platinum heater were spin coated with the thermites and dried at 105°C in an oven for 10 min. Th...

Carbon-based electrode materials have been widely used for many years for electrochemical charge storage, energy generation, and catalysis. We have developed an electrode material with high specific capacitance by entrapping graphite nanoparticles into a sol-gel network. Films from the resulting colloidal suspensions were highly porous due to the removal of the entrapped organic solvents from sol-gel matrix giving rise to high Brunauer-Emmett-Teller (BET) specific surface areas (654 m(2)/g) and a high capacitance density ( approximately 37 F/g). An exponential increase of capacitance was observed with decreasing scan rates in cyclic voltammetry studies on these films suggesting the presence of pores ranging from micro (< 2 nm) to mesopores. BET surface analysis and scanning electron microscope images of these films also confirmed the presence of the micropores as well as mesopores. A steep drop in the double layer capacitance with polar electrolytes was observed when the films were rendered hydrophilic upon exposure to a mild oxygen plasma. We propose a model whereby the microporous hydrophobic sol-gel matrix perturbs the hydration of ions which moves ions closer to the graphite nanoparticles and consequently increase the capacitance of the film.

We studied frequency spectrum, implicit time and amplitude of oscillatory potentials (OPs) in albino mice, rats, and rabbits. Oscillatory potentials were extracted digitally from dark- and light-adapted electroretinograms (ERGs) recorded with a protocol commonly used in our laboratory. The frequency spectra of OPs were analyzed by using Fast Fourier Transform (FFT). Oscillatory potential amplitudes were calculated via numerically integrating the power spectrum. Oscillatory potential frequency spectra vary among species and are light-intensity dependent. In dark-adapted ERG, mouse and rat OPs have one major component with a frequency peak at approximately 100 Hz. Rabbits show multiple frequency peaks with a low frequency peak around 75 Hz. In all the three species, the implicit time of light-adapted OP is longer than that of the dark-adapted OPs. At a given intensity, mice have the highest OP responses. Our data suggest that the commonly used bandpass of 75 Hz (or even 100 Hz) to 300 Hz for OP extraction is insufficient in these animals. In order to acquire the complete OP responses from the ERG signals, it is necessary to determine the OP frequency spectrum. In this study, the lower end cutoff frequency was set at 40 Hz in mice, 65 Hz in rats and rabbits.

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