Enhancement of Fast Scan Cyclic Voltammetry Detection of Dopamine with Tryptophan

PURPOSE: Fast Scan Cyclic Voltammetry is used to monitor real time extracellular neurotransmitter concentrations. Tryptophan is responsible for fast kinetics of electron transfer in enzymatic redox reactions. We hypothesized that tryptophan would increase the electron transfer kinetics of the redox reaction for dopamine resulting in a larger current detected and increased sensitivity for dopamine detection. SUBJECTS: Carbon fiber microelectrodes modified with tryptophan, n= 3-5 electrodes. METHODS AND MATERIALS: Modification parameters were tested to improve the efficiency of tryptophan deposition. Final parameters used for modification were 1 mM tryptophan deposited in a potential window: -1.7 – 1.8 V, scan rate = .02V/s. Dopamine tests were performed in a potential window: -.4 – 1.0 V, scan rate = 400 V/s. ANALYSES: Statistical analysis was performed in R using student’s t-tests, α = .05. RESULTS: Tryptophan deposition is diffusion controlled and forms a monolayer coating. Tryptophan derivatives revealed the covalent binding of tryptophan to the electrode occurs at the secondary amine group in the indole side chain. Sensitivity tests revealed dopamine detected with tryptophan modified electrodes had a current density 3.5 times greater than an unmodified electrode. Extensive cycling showed the electrodes to be durable. Lastly, tryptophan modified electrodes were on average 15 times more selective for dopamine over the interfering molecule ascorbic acid. CONCLUSIONS: This research is an in vitro proof of concept for the use of tryptophan modified electrodes in fast scan cyclic voltammetry dopamine detection. The electrodes fit key criteria needed for dopamine detection; increased sensitivity, durability, and selectivity for dopamine