Collection of nanoliter microdialysate fractions in plugs for off-line in vivo chemical monitoring with up to 2s temporal resolution

Abstract

An off-line in vivo neurochemical monitoring approach was developed based on collecting nanoliter microdialysate fractions as an array of "plugs" segmented by immiscible oil in a piece of Teflon tubing. The dialysis probe was integrated with the plug generator in a polydimethlysiloxane microfluidic device that could be mounted on the subject. The microfluidic device also allowed derivatization reagents to be added to the plugs for fluorescence detection of analytes. Using the device, 2 nL fractions corresponding to 1-20 ms sampling times depending upon dialysis flow rate, were collected. Because axial dispersion was prevented between them, each plug acted as a discrete sample collection vial and temporal resolution was not lost by mixing or diffusion during transport. In vitro tests of the system revealed that the temporal resolution of the system was as good as 2 s and was limited by mass transport effects within the dialysis probe. After collection of dialysate fractions, they were pumped into a glass microfluidic chip that automatically analyzed the plugs by capillary electrophoresis with laser-induced fluorescence at 50 s intervals. By using a relatively low flow rate during transfer to the chip, the temporal resolution of the samples could be preserved despite the relatively slow analysis time. The system was used to detect rapid dynamics in neuroactive amino acids evoked by microinjecting the glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) or K + into the striatum of anesthetized rats. The resulted showed increases in neurotransmitter efflux that reached a peak in 20 s for PDC and 13 s for K + .

Separation-Based Methods Combined With Microdialysis Sampling for Monitoring Neurotransmitters and Drug Delivery to the Brain

“…Theoretically, if suf ficiently fast separations are employed, temporal resolution is limited only by Taylor dispersion (Taylor, 1953) in the microdialysis probe and associated collection or connection tubing. The limits have been explored by the Kennedy group (Lada et al, 1997;Schultz and Kennedy, 2008;Wang et al, 2010). Alternatively, online biosen sors can be employed for improved temporal resolution, although each biosensor is specific to one analyte, so multiple sensors must be employed for multianalyte monitoring ( Jones et al, 2002;Rogers et al, 2013aRogers et al, , 2013b).…”

A review of microdialysis coupled to microchip electrophoresis for monitoring biological events

“…They used this device to sample, create droplets from the microdialysis brain perfusate in an anesthetized rat, and derivatize amino acids in the droplets [144]. After droplet creation on rat, the droplets were collected and immediately analyzed off-line for amino acids using microchip electrophoresis with LIF detection.…”

“…Microchip electrophoresis with fluorescence detection was also used for off-line analysis of droplets generated by segmented flow for excitatory amino acids following microinjections of either L- trans -pyrrolidine-2,4,-dicarboxylic acid or K + . Concentrations of amino acids (glutamate, aspartate, taurine, glycine, and GABA) were monitored using this device with both stimulation procedures [144]. Lastly, microdialysis samples were segmented and derivativized shortly after their collection and stored for up to four days before being analyzed for amino acids by microchip electrophoresis with LIF detection [145].…”

Using copper ions to amplify ROS-mediated fluorescence for continuous online monitoring of extracellular glucose in living rat brain

“…In the case of acute brain injury, the response of a rapid release of massive intracellular K þ ions into brain ECF (Katayama et al, 1990;Reinert et al, 2000) has a profound influence on the dynamic actions of neurotransmitters (Zheng et al, 2000;Wang et al, 2008Wang et al, , 2010Slaney et al, 2011), the membrane-associated transport system, the metabolic activities, and the synaptic functions of neurons (Kimelberg et al, 1979;Marion, 1998). Because the brain extracellular glucose dominates the Na þ /K þ homeostasis and its associated biochemical interactions, the ability to describe the dynamic variations in the concentration of glucose would enhance the study of these essential functions in living rat brains.…”