Characterizing human endorphins with fast-scan cyclic voltammetry and carbon fiber microelectrodes

Endorphins are three proteins that belong to a family of neuropeptides that regulate pain perception, mood, and immune function by targeting opioid receptors. The biological role of ꞵ-endorphin is well studied, but α- and γ-endorphins are less understood. By creating more fast and reliable methods of detection, we can progress towards determining the physiological role of each endorphin. Carbon fiber microelectrodes (CFMEs) are promising sensors for biomolecule detection as they are small, cheap sensors that can target specific brain regions. Fast-scan cyclic voltammetry (FSCV) is an electroanalytical technique, often coupled with CFMEs, that has been used to measure a variety of neurotransmitters (NTs) and neuropeptides. This method is of interest due to its exceptionally high temporal resolution, but it is also relatively affordable, minimally invasive, and biocompatible. Because the endorphins contain tyrosine, they can be easily measured with FSCV using a modified sawhorse waveform (MSW). Endorphins were detected at as low as nanomolar concentrations with high stability, exhibiting a mixed adsorption- and diffusion-controlled mechanism, and can be co-detected with small molecule NTs such as dopamine (DA). ꞵ-Endorphins saturated the electrode quicker due to its bulkier size, and the CFME was found to be significantly more sensitive to α-endorphin than γ-endorphin. Finally, we detected endorphins in brain samples for proof of principle analysis of the assay.