Development of Carbon-MEMS based device for the In Vivo Electrochemical Detection of Neurotransmitter Fluctuations

Electrochemical detection schemes are well suited for the detection of neurotransmitters in vivo because of their inherent fast time response, and ability to investigate small regions using ultramicroelectrode technologies. Traditionally, in vivo neurotransmitter detection has been done at a carbon-fiber microelectrode; which has proven to be the optimal electrochemical biosensor for its small size, wide potential window, and anti-biofouling properties. Though much has been learned though the use of the carbon fiber microelectrode, it only possesses the ability to observe a single microenvironment in vivo. Arrays of electrochemical detectors could, therefore, prove to be very useful in vivo, enabling the study of multiple microenvironments simultaneously.;This research aims to create a robust fabrication process for the creation of a device that enables multi-site detection of neurotransmitters in vivo. Gold microelectrodes were investigated as a possible alternative to carbon-fibers because of the material's compatibility with microfabrication techniques and surface modifications; which would enable the easy fabrication of array based technology. The gold microelectrodes, like the carbon-fiber, were found to be compatible with the electrochemical technique of fast scan cyclic voltammetry (FSCV); which allowed for the selective detection and identification of neurotransmitters in vitro. The gold microelectrodes could not, however, outperform the carbon fiber in vivo; thus future studies focused on carbon based fabrication strategies.;To ensure that array based technologies were viable in vivo, an array of carbon fiber microelectrodes were fabricated using both traditional fabrication and microfabrication strategies. This device implemented carbon fiber microelectrodes, fabricated using fused silica capillaries rather than borosilicate glass, in a microfabricated spacer. The spacer enabled the precise placement of the individual carbon fiber electrodes within a small space (<1 mm). The device was then used in vivo to observe multisite neurotransmitter release and the multisite effect of pharmacological agents on the D2 autoreceptor (raclopride) and dopamine transporter (cocaine).;Further research was dedicated to the batch fabrication of carbon based arrays. Pyrolyzed photoresist thin films (PPF) were investigated as a possible alternative to carbon fibers for array based detection, as PPF is directly compatible with photolithography and theorized to be structurally similar to the carbon fiber. Arrays of PPF ultramicroelectrodes were constructed using microfabrication techniques and compared to carbon fibers using FSCV in vitro. The PPF arrays were able to detect and identify the neurotransmitter dopamine with comparable sensitivity and selectivity in vitro. The usefulness of the arrays was demonstrated in its ability to perform multisite detection of dopamine and the electrochemically decoupled detection of dopamine and oxygen fluctuations.;A microfabrication strategy was subsequently developed around the PPF thin film to produce devices that were of suitable dimensions for in vivo use. The batch fabrication process robustly yielded thin silicon probes that enabled the in vivo multisite detection of electrically stimulated dopamine release. Using these devices, dopamine release and reuptake was shown to be heterogeneous throughout the striatum under both normal and pharmacologically altered conditions.