(607g) Polymer-Induced Liposome Aggregation: Toward the Application of Naked-Eye Bio-Detection

Signal amplification has been one of the important issues for detecting proteins or pathogens at low concentration regime. Here, we investigate a liposome clustering process induced by an amphiphilic triblock copolymer through hydrophobic interactions. The clustering is visible and thus can be used as an amplification platform for naked-eye detection. In this study, the liposomes are composed of dipalmitoylphosphatidylcholine (DPPC, di-C₁₆) and dihexanoylphosphatidylcholine (DHPC, di-C₆) induced by triblock copolymer linkers, (propylene glycol)_m â?? (ethylene glycol)_n â?? (propylene glycol)_m (PO_m â?? EO_n â?? PO_m, reverse pluronic copolymers). The aggregation occurs when the two PPO hydrophobic blocks insert in the bilayers of different liposome resulting in a liposomal clusters. The clustering is presumably facilitated by the mismatch of acyl chain between DPPC and DHPC, as evident in the rapid increase of UV absorption and hydrodynamic radius (R_H). In contrast, the clustering of DPPC liposomes is hardly observed in the presence of polymer linkers. The experimental results are further corroborated by the simulation work, indicating that less energy is required for the polymer insertion into the interfaces between DPPC and DHPC compared to the pure DPPC regime. Moreover, we observed distinct aggregation kinetics between polymer linkers with different hydrophobicity. Specifically, increase of the polymer concentration leads to more obvious clusters for the relatively hydrophilic polymer linker (PO₁₄ â?? EO₂₄ â?? PO₁₄), but inhibits the aggregation for hydrophobic polymer linkers (i.e. PO₂₅ â?? EO₇ â?? PO₂₅ and PO₂₆ â?? EO₂₀ â?? PO₂₆). This phenomenon is explained by the mechanism that the hydrophobic polymers strongly anchor at and fast occupy the â??activeâ? (DHPC-rich) sites of bilayer compared to the hydrophilic ones, whose hydrophobic PPO may frequently associate with and dissociate from the â??activeâ? sites, enhancing the stringing process between liposomes.