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.