Electrochemical measurement of quantal exocytosis using microchips

Abstract

Carbon-fiber electrodes (CFEs) are the gold standard for quantifying the release of oxidizable neurotransmitters from single vesicles and single cells. Over the last 15 years, microfabricated devices have emerged as alternatives to CFEs that offer the possibility of higher throughput, subcellular spatial resolution of exocytosis, and integration with other techniques for probing exocytosis including microfluidic cell handling and solution exchange, optical imaging and stimulation, and electrophysiological recording and stimulation. Here we review progress in developing electrochemical electrode devices capable of resolving quantal exocytosis that are fabricated using photolithography.

A High‐Affinity Fluorescent Sensor for Catecholamine: Application to Monitoring Norepinephrine Exocytosis

“…14 Amperometric microelectrodes immediately adjacent to release sites on the cell surface measure pA-magnitude spikes of current as the catecholamine released from an individual vesicle is oxidized on the surface of the electrode. [14][15][16] Figure 4 presents three examples of amperometric spikes recorded synchronously in time with punctate changes in NS510 fluorescence indicated by the regions of interest. In Example A, note that two release events were recorded, each with a drop in fluorescence in the region of interest presumably due to two nearby vesicles sequentially undergoing exocytosis.…”

A High‐Affinity Fluorescent Sensor for Catecholamine: Application to Monitoring Norepinephrine Exocytosis

“…Abrupt, punctate losses of fluorescence were observed upon stimulation with high‐K + solution that are likely to reflect exocytosis of a vesicle containing norepinephrine labeled with 10 μ m NS510. In order to validate that punctate drops in NS510 correspond to release of catecholamine from individual vesicles, experiments were performed using an amperometric ring microelectrode patterned underneath the cell being imaged . Amperometric microelectrodes immediately adjacent to release sites on the cell surface measure picoampere‐magnitude spikes of current as the catecholamine released from an individual vesicle is oxidized on the surface of the electrode .…”

“…In order to validate that punctate drops in NS510 correspond to release of catecholamine from individual vesicles, experiments were performed using an amperometric ring microelectrode patterned underneath the cell being imaged . Amperometric microelectrodes immediately adjacent to release sites on the cell surface measure picoampere‐magnitude spikes of current as the catecholamine released from an individual vesicle is oxidized on the surface of the electrode . Figure presents three examples of amperometric spikes recorded synchronously in time with punctate changes in NS510 fluorescence indicated by the regions of interest.…”

A Bidirectional-Current CMOS Potentiostat for Fast-Scan Cyclic Voltammetry Detector Arrays

“…Surface-patterned planar MEAs using noble metals such as gold and platinum and other materials have recently been applied to measure quantal release events from single cells [10]. Scalable arrays incorporate CMOS potentiostats with on-chip electrodes for parallel recordings from large numbers of cells [11]–[14].…”

“…The resulting current reflects the electrode impedance and thus the basic functionality of the electrode. In addition, test analytes such as ferricyanide, which is reduced to ferrocyanide, forming a well-behaved redox pair [10], as well as other compounds [15], have been used in conjunction with cyclic voltammetry for characterization of the performance of electrochemical electrodes. Such measurements cannot easily be performed with unipolar CMOS chips because they require not only the application of bipolar voltages but also the measurement of bidirectional currents.…”