Dual-Interface Hierarchical Assembly of Asymmetric ICG-Lipid Conjugates Enables Finite J-type Aggregation and Two-Stage NIR-II Fluorescence Enhancement

Aggregation-induced quenching severely limits the imaging properties of indocyanine green (ICG), despite its FDA approval and its emission in the near-infrared II (NIR-II) region. Herein, we introduce a dual-interface assembly strategy that orchestrates the sequential assembly of asymmetric ICG-lipid conjugates at lipid and liposome-protein interfaces to achieve two-stage NIR-II fluorescence enhancement. The ICG-sphingosine conjugates without sulfonate groups (ICG-C-Sp) form finite, weakly coupled J-type aggregates within lipid bilayers, producing markedly enhanced NIR-II fluorescence. Upon serum protein adsorption, H-aggregation is further suppressed and the finite J-type component is reinforced, yielding a secondary fluorescence enhancement. This strategy generates bright NIR-II emission beyond 1300 nm and prolongs circulation. After M2pep modification, the nanoprobes enable high-contrast imaging of subcutaneous and orthotopic bladder tumors. Notably, the nanoprobes can detect ultrasmall lung metastatic tumors and human bladder cancer in <i>ex vivo</i> tissues. This sequential assembly strategy enables the development of clinically translatable NIR-II fluorescent probes.