Stereoselective cyclic peptide assisted DART-MS for rapidly screening environmental disruptors of dopamine receptors

The emerging binding-directed analysis (BDA) technique has successfully employed stereoselective oligopeptide probes to capture G protein-coupled receptor (GPCR)-active compounds from complex environmental matrices via electrospray ionization (ESI)-enabled complex formation. However, its integration with direct analysis in real time-mass spectrometry (DART-MS), a technique characterized by fundamentally different ionization mechanisms and exceptionally high analytical throughput, remains unexplored. This study evaluates a DART-MS-based BDA workflow for rapid, chromatography-free screening of GPCR ligands using ten model dopamine (DA) receptor ligands and a dopamine-selective cyclic peptide probe (CPP). The workflow required less than 1 min per measurement. Notably, DART-MS even achieved an average CPP-ligand complexation efficiency substantially higher than that obtained in ESI-MS (20% vs 4%), facilitating reliable identification of CPP-ligand complex ions from redundant mass spectra. Moreover, most CPP-ligand gas-phase complexes formed in DART-MS and ESI-MS showed comparable collision stability. Only the CPP-sulpiride and CPP-pramipexole complexes showed stability reduction by 85% and 61% in DART-MS compared to ESI-MS. These findings suggest that DART desorption/ionization conditions may promote more efficient formation and/or preservation of CPP-ligand complex ions. The applicability of the DART-MS-based BDA workflow was further validated through analysis of surface water samples. Although the spiked model ligand perphenazine (L1) was not captured by the CPP, the rubber additive 1,3-diphenylguanidine was successfully identified, a DA antagonist formerly also discovered by the ESI-MS-based BDA workflow. Collectively, this study establishes DART-MS-based BDA as a highly-efficient screening tool for future large-scale surveillance of GPCR-disrupting chemicals in the environment.