Abstract
Fast-scan cyclic voltammetry (FSCV) is a common analytical electrochemistry tool used to measure chemical species. It has recently been adapted for measurement of neurotransmitters such as dopamine in awake and behaving animals (in vivo). Electrode calibration is an essential step in FSCV to relate observed current to concentration of a chemical species. However, existing methods require multiple components, which reduce the ease of calibrations. To this end, a microfluidic flow cell (μFC) was developed as a simple device to switch between buffer and buffer with a known concentration of the analyte of interest--in this case dopamine--in a microfluidic Y-channel. The ability to quickly switch solutions yielded electrode calibrations with faster rise times and that were more stable at peak current values. The μFC reduced the number of external electrical components and produced linear calibrations over a range of concentrations. To demonstrate this, an electrode calibrated with the μFC was used in FSCV recordings from a rat during the delivery of food reward--a stimulus that reliably evokes a brief increase in current due to the oxidation of dopamine. Using the linear calibration, dopamine concentrations were determined from the current responses evoked during the behavioral task. The μFC is able to easily and quickly calibrate FSCV electrode responses to chemical species for both in vitro and in vivo experiments.
Highlights
Fast-scan cyclic voltammetry (FSCV) is a common analytical electrochemistry tool that has more recently been applied to investigate the role of neurotransmitters in awake and behaving subjects.[1,2,3] Its ability to detect chemical changes with high temporal and spatial resolution accounts for its prevalence in measuring neurotransmitters such as dopamine in awake and behaving animals.[4,5] In FSCV, a voltage ramp is rapidly applied to a carbon fiber electrode causing chemical species at the electrode surface to oxidize and reduce – which is measured as current
Due to the large chamber volume, the macro flow cell slowly switches between solutions, creating a slow rise time in the calibration curve, which does not stabilize at a peak current value
Multiple calibrations were tedious since the flow injection apparatus could only preload 300 μl of dopamine solution at a time
Summary
Fast-scan cyclic voltammetry (FSCV) is a common analytical electrochemistry tool that has more recently been applied to investigate the role of neurotransmitters in awake and behaving subjects.[1,2,3] Its ability to detect chemical changes with high temporal and spatial resolution accounts for its prevalence in measuring neurotransmitters such as dopamine in awake and behaving animals (in vivo).[4,5] In FSCV, a voltage ramp is rapidly applied to a carbon fiber electrode causing chemical species at the electrode surface to oxidize and reduce – which is measured as current. A flow injection apparatus is used to calibrate electrodes.[6,7] The system consists of a syringe pump and a rotary valve loop injector preloaded with dopamine, and an electrode tip is inserted into the end of the loop injector. The flow injection apparatus briefly exposes the electrode to a known concentration of dopamine before returning to buffer alone. Due to the large chamber volume, the macro flow cell slowly switches between solutions, creating a slow rise time in the calibration curve, which does not stabilize at a peak current value. The on-chip measurements improve on the previous methods since there is minimal dilution of the sample of interest These devices require separate equipment to drive the switching between solutions. The μFC simplifies the electrode calibration while improving the rise times and its stabilization at peak current values
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