Phototherapy Mode Control by Tuning Molecular and Supramolecular Forms of Indocyanine Green in Crosslinked Polyion Complex Nanoparticles

Photothermal therapy (PTT) offers a minimally invasive approach for treating hypoxic tumors, while photodynamic therapy (PDT) is limited by its oxygen dependence. Indocyanine green (ICG) is a clinically approved near-infrared (NIR) dye with potential for PTT and PDT, but its application is hindered by poor photostability, rapid clearance, and aggregation, resulting in unfavorable pharmacokinetics and limited phototherapeutic performances. Here, we address these limitations through a combination of chemical transformation of ICG by dimerization, controlled supramolecular assembly into dye aggregates, and a tailored formulation strategy. We systematically compared three forms, monomeric ICG, its covalent dimer (dICG), and the corresponding J-aggregate (dIJA), each formulated into polyion complex nanoparticles (PNPs) using poly(2-ethyl-2-oxazoline)-b-poly(L-ornithine) as the polyelectrolyte carrier matrix. Subsequent genipin-mediated core crosslinking produced crosslinked nanoparticles (CPNPs) with enhanced stability, high encapsulation efficiency, and preserved optical characteristics. CPNPs consistently outperformed free dye and non-crosslinked PNPs, showing improved colloidal stability, enhanced photostability, and higher photothermal performances. In FaDu cells, ICG-loaded CPNPs mediated oxygen-dependent photodynamic effects, whereas dICG-and dIJA-loaded CPNPs induced oxygen-independent photothermal cytotoxicity under NIR irradiation. Our integrated comparison demonstrates that controlling the molecular form and supramolecular assembly of ICG derivatives enables tunable NIR phototherapy, identifying dICG- and dIJA-based CPNPs as promising platforms for the treatment of hypoxic tumors by photoacoustic imaging (PAI) guided PTT