Development of microfluidic-based technologies for in vivo monitoring of primary amine neurotransmitters in mammalian brains.

Neurotransmission is essential in the functioning of the central nervous system; therefore, the ability to monitor compounds involved in this process is of interest to the neuroscience community. Previously, capillary separation-based sensors that coupled microdialysis sampling with fast capillary electrophoresis (CE) separations have been developed capable of near real time in vivo monitoring of primary amine neurotransmitters with high temporal and spatial resolution. Such systems, however, require expertise to operate and are ill-suited for on-site applications. To improve the ease of use and potential portability of this technology, this work details the development of microfluidic separation-based sensors that incorporate the analytical functions of these capillary-based systems. First generation devices were developed that contained a reaction channel, electrokinetically gated injector, and separation channel inside monolithic 2.5 cm x 7.6 cm x 0.2 cm pieces of glass. These devices could be coupled directly to microdialysis probes for in vivo sampling. An on-chip precolumn reaction was used to derivatize primary amino acids with o-phthaldialdehyde (OPA) and beta-mercaptoethanol (betaME), which produced fluorescent isoindoles that were detectable with an epifluorescent confocal microscope. In vitro detection limits were ∼200 nM with efficiencies up to 156,000 theoretical plates. To demonstrate the capability of these devices to detect changes in neurotransmitter levels, the effects of a glutamate uptake inhibitor on glutamate basal levels was monitored in the striatum of a rat. To improve the ability of these devices to monitor low level neurotransmitters, modifications were made to allow for on-chip derivatization with naphthalene-2,3-dicarboxaldehyde (NDA) and cyanide (CN), which decreased in vitro detection limits for primary amino acids to ∼13 nM. Moreover, a change in the design of the reaction channel allowed for reaction conditions to be tuned independently from separation conditions thereby improving the utility of these devices. Despite this progress, these microfluidic separation-based sensors lack the high separation performance and low analysis times of capillary-based systems. To address these issues, future research directions are proposed to improve the performance and possible portability of these devices.Ph.D.Analytical chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/127063/2/3328945.pd