Rational Design of a "Turn-on" Supramolecular Fluorescent Probe for Gossypol Sensing Based on the Restriction of...

The development of ″turn-on″ supramolecular fluorescent probes for detecting biologically important molecules lacking reactive sites, with a clear mechanistic understanding, remains challenging. To address this challenge, this study establishes and validates a rational design strategy based on the restriction of intramolecular bending (RIB) mechanism for developing supramolecular fluorescent probes. The core of this strategy is to activate fluorescence by physically confining a fluorophore, thereby suppressing its nonradiative decay channels. A BODIPY-based fluorophore IPR featuring sterically crowded isopropyl groups at the meso-position and methyl substituents at the ortho-positions was designed, which enhances bending vibrations and promotes fluorescence quenching in solution. Upon encapsulation within the hydrophobic cavity of human serum albumin (HSA), these bending vibrations are effectively suppressed, leading to a fluorescence ″turn-on″ response and the formation of the IPR@HSA supramolecular probe. To showcase the analytical potential of this strategy, the toxic compound gossypol was used as a model analyte. Gossypol induces an allosteric effect by binding to HSA, which further intensifies the confinement of the IPR molecule, leading to a secondary signal enhancement and enabling the rapid, highly selective detection of gossypol. The method exhibited a linear detection range for gossypol from 0-5 μM (R² = 0.9983) with a response time of under 10 s, achieving satisfactory recovery rates from 80.72 to 119.49% in real pork samples. This work not only provides a tool for food safety monitoring but also offers a systematic and generalizable method, supported by comprehensive computational and experimental evidence, for developing ″turn-on″ supramolecular fluorescent probes.