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

A potentiostat circuit for the application of bipolar electrode voltages and detection of bidirectional currents using a microelectrode array is presented. The potentiostat operates as a regulated-cascode amplifier for positive input currents, and as an active-input regulated-cascode mirror for negative input currents. This topology enables constant-potential amperometry and fast-scan cyclic voltammetry (FSCV) at microelectrode arrays for parallel recording of quantal release events, electrode impedance characterization, and high-throughput drug screening. A 64channel FSCV detector array, fabricated in a 0.5-μm, 5-V CMOS process, is also demonstrated. Each detector occupies an area of 45 μm × 30 μm and consists of only 14 transistors and a 50-fF integrating capacitor. The system was validated using prerecorded input stimuli from actual FSCV measurements at a carbon-fiber microelectrode.

I. Introduction

Neurons, the fundamental units of the nervous system, communicate with each other via a chemical signaling process mediated by the storage and release of neurotransmitters, a set of biomolecules that act as chemical messengers to regulate neuronal function and behavior [1]. Neurons store high concentrations of these biomolecules in small membrane-bound secretory vesicles attached to the inside of the presynaptic plasma membrane. When the presynaptic terminal is electrically stimulated, the vesicles fuse with the plasma membrane through a process called exocytosis, releasing the vesicle contents into extracellular space [2]. Neurotransmitter release from a single vesicle is termed quantal release. The number of biomolecules expelled in a quantal release event is the quantal size [3]. Quantal release has been the subject of extensive medical research because some of the underlying molecular mechanisms mediating exocytosis are still not fully understood. A better understanding of properties such as the quantal size and the frequency and time course of quantal release events is necessary for the discovery and development of new therapeutic drugs that modulate these properties.