Abstract
Opioid neuropeptides play a significant role in pain perception, appetite regulation, sleep, memory, and learning. Advances in understanding of opioid peptide physiology are held back by the lack of methodologies for real-time quantification of affinities and kinetics of the opioid neuropeptide-receptor interaction at levels typical of endogenous secretion (<50 pM) in biosolutions with physiological ionic strength. To address this challenge, we developed all-electronic opioid-neuropeptide biosensors based on graphene microelectrodes functionalized with a computationally redesigned water-soluble μ-opioid receptor. We used the functionalized microelectrode in a bias-free charge measurement configuration to measure the binding kinetics and equilibrium binding properties of the engineered receptor with [d-Ala(2), N-MePhe(4), Gly-ol]-enkephalin and β-endorphin at picomolar levels in real time.