Metal complexes with a twist: modified rhodamines as a promising theranostic approach for combating cancer

Abstract

Rhodamines have been recognized for their exceptional optical properties, making them suitable for detection, imaging, and disease diagnosis. However, their use as photosensitizers in Photodynamic Therapy (PDT) has been limited by their low singlet oxygen production and limited tissue penetration. The development of rhodamine-metal complexes has overcome these limitations, offering a promising new approach for cancer treatment. These complexes in combination with structural and optical tuning of rhodamines, have been engineered to enhance tumour cell selectivity, improve reactive oxygen species (ROS) generation, and mitochondrial-targeted delivery. Notably, a variety of metal ions, including iridium(III), ruthenium(II) and platinum(II/IV) can form complexes with bright rhodamines with excellent optical responses and remarkable ROS generation. These breakthroughs have the potential to improve cancer diagnosis and therapeutic applications. Photophysical properties, photostability, and targeting agents, particularly in the near-infrared (NIR) range, will be discussed, with a focus on their applications in cancer detection, localization, and cytotoxicity.