Stabilising indocyanine green J-aggregate theranostics in biological milieu via liposomal envelopment

Indocyanine green (ICG) J-aggregate (IJA) is a self-assembled ICG with a red-shift absorption band, enabling better tissue penetration than the monomeric ICG. Despite its superior photoacoustic imaging capabilities and heating stability to ICG, IJA suffers from low optical stability in aqueous and biological media, jeopardising its biomedical applications. The present work focused on loading p-IJA into liposomes to enhance its promising therapeutic and imaging applications. To optimise IJA loading into liposomes, we investigated the effect of lipid bilayer composition (lipid melting points, cholesterol, DSPE-PEG₂₀₀₀, and lipid charge) on the encapsulation of pre-formed IJA (p-IJA) into liposomes. Our findings showed the significance of high melting point lipids, high cholesterol, and DSPE-PEG₂₀₀₀ contents for persevering p-IJA following loading into liposomes. Moreover, low percentages (∼5 mol %) of positively charged (DOTAP) or negatively charged (DSPG) lipids could still be incorporated into our liposomes without affecting p-IJA loading. Promisingly, p-IJA-liposomes enhanced p-IJA optical stability in a range of biological media, such as serum proteins, blood and collagen. Finally, lyophilised p-IJA-liposomes for long-term storage were successfully prepared. The present study solely focused on evaluating the enhanced photothermal stability of p-IJA following liposome envelopment. Nevertheless, our lipid-enveloped p-IJA could offer a biodegradable and stable platform for multimodal applications, including photoacoustic imaging, photothermal therapy (PTT), photodynamic (PDT), nanobubble-mediated ablation, and combination therapy with chemotherapeutics agents.