Synergistic Integration of Layer-by-Layer Assembly of Photosensitizer and Gold Nanorings for Enhanced Photodynamic Therapy in the Near Infrared

A layer-by-layer (LbL) assembly strategy was used to incorporate high concentrations of Al(III) phthalocyanine chloride tetrasulfonic acid (AlPcS₄) photosensitizer (PS) onto plasmonic Au nanorings (Au NRs) for increasing the cellular uptake of AlPcS₄ and subsequently enhancing the efficacy of photodynamic therapy (PDT) of human breast cancer cells (MDA-MB-231) in the near-infrared (NIR) range. Au NRs with two layers of AlPcS₄ (Au NR/(AlPcS₄)₂) markedly increased the cellular internalization of AlPcS₄ and elevated the generation of reactive oxygen species (ROS). Quenching the photosensitivity of AlPcS₄ on the Au NR surface during the uptake and then significant ROS formation only upon PS release inside the cellular compartment made it possible to achieve a high PDT specificity and efficacy. PDT of breast cancer cells following 4 h of incubation with various formula revealed the following cell destruction rate: ∼10% with free AlPcS₄, ∼23% with singly layered Au NR/(AlPcS₄)₁ complex, and ∼50% with doubly layered Au NR/(AlPcS₄)₂. Incubation with Au NR/(AlPcS₄)₂ for an additional 2 h resulted in ∼85% cell killing, more than 8-fold increase compared to AlPcS₄ alone. Together, integration of LbL of PS with Au NRs holds a significant promise for PDT therapeutic treatment of a variety of cancers.