Characterization of Electroactive Amino Acids with Fast-Scan Cyclic Voltammetry

Abstract

Small molecules and signaling peptides are extensively involved in controlling basic brain function. While classical neurotransmitters can be detected with a variety of techniques, methods for measurement of rapidly-released neuropeptides remain underdeveloped. Fast-scan cyclic voltammetry (FSCV) is an electrochemical technique often used for subsecond detection of small molecule neurotransmitters, in vivo. A few peptides have been detected with FSCV; however, a detailed analysis of the electrochemical signature of all electroactive amino acids with FSCV has not been fully investigated. Because the mechanisms, locations, and timescales for signaling peptide release in the brain are relatively unexplored, developing sensitive and selective tools capable of quantitating neuropeptide signaling is essential. To bridge this gap, we used FSCV to characterize the electroactive amino acids: cysteine, methionine, histidine, tryptophan, and tyrosine. We show that tyrosine, tryptophan, and histidine are easily oxidized on carbon fiber surfaces with FSCV, while detection of the sulfur-containing amino acids is more difficult. This study provides critical information for electrochemical waveform design and optimization for detection of peptides containing these amino acids.

Measurement of Tryptophan in Cell Cultures Using Fast Scan Cyclic Voltammetry at Carbon Fiber Microelectrodes with Improved Sensitivity and Selectivity

“…Theory predicts that a slope of 1 is indicative of an entirely adsorption-driven process while a slope of 0.5 indicates a solely diffusion-driven process 7,25,26 . Our slope indicates that the signal we obtained is primarily adsorption-driven with some contribution from diffusion and this is in agreement with those reported by others 16,26 . Lastly, we performed Trp measurements in cultured PC-12 cells.…”

“…100 V/s). Thus, the smaller oxidation peak in Trp (~0.43 V in Weese-Myers et al 16 ) is no longer apparent here. The switching potential is the upper limit potential and serves to: 1) over-oxidize the surface groups to increase adsorption; and/or 2) renew the electrode surface by stripping the topmost layer of carbon.…”

“…One of the techniques capable of making measurements at the appropriate spatiotemporal scale is fast scan cyclic voltammetry (FSCV) at carbon fiber microelectrodes (CFMs). The Ross lab demonstrated the utility of FSCV at CFMs (via the application of the dopamine waveform) to measure electroactive amino acids, including Trp, with 100 ms timescale and micron spatial resolution 16 . However, their paper did not demonstrate selective measurement of Trp over dominant interfering species such as Tyr, which has overlapping oxidation peaks.…”

Measuring tryptophan dynamics using fast scan cyclic voltammetry at carbon fiber microelectrodes with improved sensitivity and selectivity

“…42,74,75 Our slope indicates that the signal we obtained is primarily adsorption-driven with some contribution from diffusion and this is in agreement with those reported by others. 60,75 As summarized in Fig. 5a and b, the original MSW did yield signicantly lower current density than the dopamine waveform at all concentrations (****p < 0.0001).…”

Analytical strategies in neurotransmitter measurements: A mini literature review

“…Zebrafish retinal neurochemical dynamics have also been monitored via FSCV (Zestos et al, 2020). Weese‐Myers et al used FSCV to characterize electroactive amino acids such as cysteine, methionine, histidine, tryptophan, and tyrosine (Weese‐Myers & Ross, 2021). That experiment provided important optimization information for the detection of electroactive amino acids.…”