Cavity-locking induced emission enables turn-on quantification of β-lactoglobulin with AIE/TICT synergy

Accurately quantifying β-lactoglobulin (β-LG) in complex milk matrices remains challenging. Here, we report a donor-π-acceptor cationic probe platform that couples AIE with suppression of TICT upon insertion into the calyx of β-LG. A triphenylamine-based probe series (LGL-1-LGL-4) systematically tunes ICT and charge distribution to optimize cavity fit. In aqueous buffer probes are weakly emissive (Φ_fl < 1 %) but turn on strongly with β-LG; LGL-4 shows red emission at 682 nm, ∼809-fold enhancement, and an association constant of 7.38 × 10⁵ M^-1 (1:1 model). Molecular docking supports deep calyx accommodation with a Vina docking score of -10.0 kcal mol^-1 and multipoint anchoring that restricts torsion. We further realize a capillary μPAD with smartphone readout that quantifies β-LG within 5 min. The method achieved excellent recoveries (98-108 %) and precision (RSD ≤ 4.7 %) in whole milk and formula, providing a rapid, field-deployable tool for food safety analysis.