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In this paper, we describe the localized and selective electrical stimulation of single cells using a three-dimensional electrode array. The chip consisted of 84 nail-like electrodes with a stimulation surface of 0.8 μm2 and interelectrode distances as small as 3 μm. Immunohistochemical staining of actin filaments in cells on these electrode arrays showed a tight coupling between the cell membrane and the chip surface. Selective and localized stimulation of primary embryonic cardiomyocytes using biphasic voltage pulses was achieved. The response of the cells to the applied electrical field was monitored using calcium imaging. An increase in relative [Ca2 + ]i of 200% was seen upon applying stimulation pules of 1.2 V. Arrays of these three-dimensional electrodes could ultimately be used as a tool to selectively electroporate the membrane of single cells for genetic manipulation or to obtain electrical access to the inner compartment of the cell. [ABSTRACT FROM AUTHOR]

We present a method for the amplification of L-glutamate directly on a surface. Our strategy is based on the surface patterning of a bi-enzymatic system consisting of glutamate oxidase (GLOD) and glutamic-pyruvate transaminase (GPT). This bi-enzymatic system amplifies L-glutamate via a recycling process. The surface chemistry on Ta2O5 was optimized for maximal enzyme loading. Enzyme activity was determined using a colormetric assay for the presence of GLOD. Co-immobilization of GLOD and GPT results in at least a doubling of the signal. Furthermore, increasing the surface concentrations of each enzyme leads to amplification levels that approach those obtained in solution. These enzymes can be patterned on substrates using a flip chip bonder for aligned microcontact printing. This bi-enzymatic system can be applied to biosensor surfaces for the in vitro detection of L-glutamate. [ABSTRACT FROM AUTHOR]

Rat embryonic cardiac myocytes display a spontaneous activity, which manifests itself as a repetitive change in a number of cellular properties, resulting in an oscillatory contractile behavior with a beating frequency of about 1 Hz. Fluo-4 loaded cardiac cells in primary culture demonstrated large fluctuating increases of the intracellular free calcium concentration. Long-term recordings of extracellular field potentials with microelectrode arrays from 60 planar electrodes showed repetitive electrical membrane depolarizations that coincided with the whole-cell Ca2 +  transients. Whole-cell patch clamp analysis revealed the existence of regular membrane depolarizations. A close correlation between the three processes was noticed. Such a correlation was confirmed in the absence of extracellular calcium, which reversibly halted the appearance of the whole-cell Ca2 +  transients and the electrical processes. Involvement of membrane depolarizations was suggested, because cellular depolarization prevented the spontaneous activity of the cardiomyocytes. In conclusion, our experiments suggest that the oscillations in intracellular calcium and the membrane depolarizations that we observe in rat embryonic cardiac myocytes reflect Ca2 +  influx after membrane depolarization. The processes responsible for the membrane depolarizations remain to be elucidated. [ABSTRACT FROM AUTHOR]

Microelectrode arrays were used for monitoring the impact of Alzheimer΄s amyloid oligomers on hippocampal neurons. Micromolar concentrations of Aβ 42 oligomers, but not fibrils, potently inhibited spontaneous electrical activity of the cells; the effect was partially reversible. The significance of the method for Alzheimer΄s disease research is studied. [ABSTRACT FROM AUTHOR]