High-Density Neurochemical Microelectrode Array to Monitor Neurotransmitter Secretion

Neuronal exocytosis facilitates the propagation of information through the nervous system pertaining to bodily function, memory, and emotions. Using amperometry, an electrochemical technique that directly detects electroactive molecules, the sub-millisecond dynamics of exocytosis are revealed and the modulation of neurotransmitter secretion due to neurodegenerative diseases or pharmacological treatments can be studied. The method of detection using amperometry is the exchange of electrons due to a redox reaction at an electrochemically sensitive electrode. As electroactive molecules, such as dopamine, undergo oxidation, electrons are released from the molecule to the electrode and an oxidation current is generated and recorded. Despite the significance of traditional single-cell amperometry, it is a costly, labor-intensive, and low-throughput, procedure. The focus of this dissertation is the development of a monolithic CMOS-based neurochemical sensing system that can provide a high-throughput of up to 1024 single-cell recordings in a single experiment, significantly reducing the number of experiments required for studying the effects of neurodegenerative diseases or new pharmacological treatments on the exocytosis process. The neurochemical detection system detailed in this dissertation is based on a CMOS amplifier array that contains 1024 independent electrode-amplifier units, each of which contains a transimpedance amplifier with comparable noise performance to a high-quality electrophysiology amplifier that is used for traditional single-cell amperometry. Using this novel technology, single exocytosis events are monitored simultaneously from numerous single-cells in experiments to reveal the secretion characteristics from groups of cells before and after pharmacological treatments which target the modulation of neurotransmitters in the brain, such as drugs for depression or Parkinson\u27s disease

Development of a Dual-Mode CMOS Microelectrode Array for the Simultaneous Study of Electrochemical and Electrophysiological Activities of the Brain

Medical diagnostic devices are in high demand due to increasing cases of neurodegenerative diseases in the aging population and pandemic outbreaks in our increasingly connected global community. Devices capable of detecting the presence of a disease in its early stages can have dramatic impacts on how it can be treated or eliminated. High cost and limited accessibility to diagnostic tools are the main barriers preventing potential patients from receiving a timely disease diagnosis. This dissertation presents several devices that are aimed at providing higher quality medical diagnostics at a low cost. Brain function is commonly studied with systems detecting the action potentials that are formed when neurons fire. CMOS technology enables extremely high-density electrode arrays to be produced with integrated amplifiers for high-throughput action potential measurement systems while greatly reducing the cost per measurement compared to traditional tools. Recently, CMOS technology has also been used to develop high-throughput electrochemical measurement systems. While action potentials are important, communication between neurons occurs by the flow of neurotransmitters at the synapses, so measurement of action potentials alone is incapable of fully studying neurotransmission. In many neurodegenerative diseases the breakdown in neurotransmission begins well before the disease manifests itself. The development of a dual-mode CMOS device that is capable of simultaneous high-throughput measurement of both action potentials and neurotransmitter flow via an on-chip electrode array is presented in this dissertation. This dual-mode technology is useful to those studying the dynamic decay of the neurotransmission process seen in many neurodegenerative diseases using a low-cost CMOS chip. This dissertation also discusses the development of more traditional diagnostic devices relying on PCR, a method commonly used only in centralized laboratories and not readily available at the point-of-care. These technologies will enable faster, cheaper, more accurate, and more accessible diagnostics to be performed closer to the patient

Single-Cell Recording Of Vesicle Release From Human Neuroblastoma Cells Using 1024-Ch Monolithic Cmos Bioelectronics

Human neuroblastoma cells, SH-SY5Y, are often used as a neuronal model to study Parkinson\u27s disease and dopamine release in the substantia nigra, a midbrain region that plays an important role in motor control. Using amperometric single-cell recordings of single vesicle release events, we can study molecular manipulations of dopamine release and gain a better understanding of the mechanisms of neurological diseases. However, single-cell analysis of neurotransmitter release using traditional techniques yields results with very low throughput. In this paper, we will discuss a monolithically-integrated CMOS sensor array that has the low-noise performance, fine temporal resolution, and 1024 parallel channels to observe dopamine release from many single cells with single-vesicle resolution. The measured noise levels of our transimpedance amplifier are 415, 622, and 1083 fARMS, at sampling rates of 10, 20, and 30 kS/s, respectively, without additional filtering. Post-CMOS processing is used to monolithically integrate 1024 on-chip gold electrodes, with an individual electrode size of 15 μm × 15 μm, directly on 1024 transimpedance amplifiers in the CMOS device. SU-8 traps are fabricated on individual electrodes to allow single cells to be interrogated and to reject multicellular clumps. Dopamine secretions from 76 cells are simultaneously recorded by loading the CMOS device with SH-SY5Y cells. In the 42-s measurement, a total of 7147 single vesicle release events are monitored. The study shows the CMOS device\u27s capability of recording vesicle secretion at a single-cell level, with 1024 parallel channels, to provide detailed information on the dynamics of dopamine release at a single-vesicle resolution