Oxytocin Peptide Detection with Carbon Electrodes and Fast Scan Cyclic Voltammetry
Authors: Zestos Alexander George , Liu Favian Alberto , Asrat Thomas 
Published: July 2021

Fast scan cyclic voltammetry (FSCV) used in conjunction with carbon fiber-microelectrodes (CFMEs) is an electrochemical technique used to detect neurotransmitters with a sub-section temporal resolution. This allows for a sensitive and selective subsecond analysis of changes in the brain. Typically, this technique is used to detect catecholamines in the brain, but recently, it has branched out into purinergic signaling and peptide neurotransmitters. This technique is not only able to detect neurochemical changes at a quick timescale, but it is able to detect a wide range of molecules with a high spatiotemporal resolution. This results in having chemical selectivity that may not be available in other electrochemical techniques. The nature of CFMEs also allows for the selective targeting of specific brain regions to ensure that precise measurements can be made.
The peptide oxytocin is important in understanding stress, depression and anxiety, and it is one of the main components in clarifying signals sent throughout the brain. Oxytocin plays vital roles for women during childbirth as well as for lactation. Oxytocin is typically analyzed by taking a blood sample and running assays that can take a while to obtain the results. Peptides, like oxytocin, can also be detected through methods like mass spectrometry and various forms of chromatography but are sometimes very time consuming and can be destructive. On the other hand, it has been known that there are some amino acids are redox active and can be measured with electrochemical techniques.
The detection of tyrosine-containing peptides using electrochemical techniques, such as oxytocin, can be quite difficult. The short amount of time that these molecules are in the extracellular space and its tendency to foul electrodes when oxidized make it hard to collect accurate and consistent data. Also, there is a higher concentration of more electroactive molecules that would make it harder to be specific for these molecules. However, due to the nature of FSCV, it is possible to change the waveform to be able to prevent the fouling of tyrosine on the surface of the electrode and improve the detection of tyrosine-containing peptides in biological samples. Recently, a modified sawhorse waveform (MSW) has been formulated that is able to specifically detect tyrosine in the methionine-enkephalin (M-ENK) neuropeptide using two specific scan rates in the anodic sweep and a short holding period at the switching potential. The MSW waveform was applied at 10 Hz with the holding potential at -0.2 V, then increased to +0.6 V at 100 V/s, and further increased to +1.2 V at 400 V/s. This potential was held in place for 3 ms before sweeping back down to the folding potential of -0.2 V at 100 V/s. This results in high specificity toward tyrosine and eliminates the fouling on the electrode. In this study, we target the tyrosine residue on oxytocin with a MSW waveform and characterize it with carbon fiber microelectrodes and fast scan cyclic voltammetry. We show the first electrochemical detection of oxytocin with FSCV with high sensitivity and spatiotemporal resolution that is distinguished from tyrosine and other amino acids. This work could potentially help further understand oxytocin’s role in vivo and importance in behavioral and disease states.