This study describes a new type of synthetic sensor that can detect a specific opioid receptor peptide (DPDPE) at extremely low concentrations. It focuses on the chemistry and physics of the sensor, not on any health or performance effects of melanotan‑I or related peptides.

Here we report, for the first time, the formation of a biomimetic covalently imprinted polymeric sensor for a target ligand, the delta-opioid G-protein coupled receptor agonist DPDPE, which reproducibly exhibits subpicomolar binding affinity in an aqueous environment. In addition to having a well-defined and homogeneous binding site, the imprinted polymer template is quite stable to storage in both the dry and wet states and has at least 6 orders of magnitude higher affinities than exhibited by similar peptide-based molecular-imprinted polymers (MIPs) thus far. A highly sensitive optical detection methodology, plasmon-waveguide resonance spectroscopy, was employed, capable of measuring binding in real time and discriminating between ligand molecules, without requiring labeling protocols (fluorophores or radioisotopes). The DPDPE-imprinted polymer showed a broad structure-activity relationship profile, not unlike that found for protein receptors. Such sensitivity and robustness of MIPs suggests potential applications ranging from biowarfare agent detection to pharmaceutical screening.