Tight and Flexible Antibody Recognition via Quaternization Interface in Metal-AIEgens Frameworks and Collaborating Ultrabright Luminescence for Intelligent Biosensing.

The analytical performance of an immunoassay is critically limited by a fundamental trade-off: achieving tight binding of antibodies (Abs) to signal reporters while preserving the conformational flexibility essential for target recognition. Herein, we resolve this paradox by engineering a quaternization interface on hafnium-based tetrakis(4-carboxyphenyl)ethylene metal-AIEgen frameworks (Hf-TCPE MAFs). Covalent grafting of betaine onto unsaturated Hf4+ sites affords Bet-Hf-TCPE. Molecular dynamics simulations and isothermal titration calorimetry reveal that the quaternized interface synergistically enhances Abs anchoring via electrostatic and hydrophobic interactions while preventing excessive conformational collapse, yielding a 16-fold increase in binding affinity (Ka) driven by an enhanced enthalpy. Concurrently, the rigid MAF framework restricts intramolecular motions, accelerating internal conversion to 185.3 fs and prolonging the fluorescence lifetime from 0.95 to 3.12 ns, resulting in a 16.6-fold enhancement in quantum yield over free TCPE. The Bet-Hf-TCPE-based immunochromatographic assay strip enables visual detection of S. typhimurium with a limit of detection of 139 CFU mL-1, representing a 4.36-fold and 175-fold improvement over Hf-TCPE- and AuNP-based strips, respectively, with excellent specificity, repeatability, stability, and feasibility in complex food matrices. Integration of a convolutional neural network automates the readout with 100% accuracy. This work establishes a powerful paradigm that synergizes interfacial mechanistic insight, ultrabright luminescence engineering, and artificial intelligence for advanced pathogen diagnosis.