Direct Synthesis of Targeted Nanosized ICG J-aggregate for Photoacoustic Imaging

Indocyanine green (ICG) J-aggregates (JAs) are self-assembled particles characterized by a sharp and strong absorption peak in the near-infrared region (∼890 nm), enhanced photostability, low fluorescence, and high photothermal conversion efficiency, compared to monomeric ICG. These attributes make ICG-JAs promising contrast agent candidates for photoacoustic imaging (PAI). However, traditional methods for synthesizing ICG-JAs often yield particles without targeting ability, which limit their applications. Thus, to synthesize targeted nanoscale JA, complex and multi-step encapsulation and filtration processes are generally required. To solve this issue, we introduce a robust and rapid strategy for direct synthesis of targeted nanoscale ICG-JA by co-assembling ICG and ICG-azide dyes under optimized formulation conditions that do not require encapsulation. The resulting nanoscale JAAZ particles (nJAAZ) exhibit diameters of ∼120-150 nm and are amenable to direct bio-orthogonal functionalization via copper-free click chemistry for the attachment of virtually any targeting ligands and/or biomolecules. We further demonstrate the strong photoacoustic signal generation of these nJAAZ in vitro and in vivo, highlighting their potential as a modular high-performance contrast agent platform for PAI. This work establishes a scalable and tunable platform for engineering functional JAs, opening new avenues for targeted molecular imaging and theranostic applications.