A light-up fluorescence probe for wash-free analysis of Mu-opioid receptor and ligand-binding events

With the aggravated burden of opioid use disorder spreading worldwide, demands for new forms of opioid receptor agonist/antagonist constitute immense research interest. The Mu-opioid receptor (MOR) is currently in the spotlight on account of its general involvement in opioid-induced antinociception, tolerance and dependence. MOR binding assay, however, is often complicated by difficulty in MOR separation and purification , as well as the tedious procedure in standard biolayer interferometry and surface plasmon resonance measurements. To this end, we present TPE2N as a light-up fluorescent probe for MOR, which exhibits satisfactory performance in both live cells and lysates. TPE2N was elaborately designed based on the synergistic effect of twisted intramolecular charge-transfer and aggregation-induced emission by incorporating a tetraphenylethene unit to emit strong fluorescence in a restrained environment upon binding with MOR through the naloxone pharmacore. The developed assay enabled high-throughput screening of a compound library, and successfully identified three ligands as lead compounds for further development.