Transition metal complex-based smart AIEgens explored for cancer diagnosis and theranostics

Bioimaging plays an important role in cancer diagnosis and treatment. Fluorescence imaging (FI) is one of the most widely applied bioimaging technologies. However, the conventional luminophores usually suffer from the aggregation-caused quenching (ACQ) effect. The aggregation-induced emission luminogens (AIEgens) have been extensively investigated to combat these shortcomings since Tang’s landmark discovery in 2001. Transition metal complex-based AIEgens (TM-AIEgens) combine the advantages of organic AIEgens and transition metal centers to improve photophysical performance and therapeutic outcomes. Herein, we highlight the recent advances in TM-AIEgens applied for cancer diagnosis and theranostics. First, the TM-AIEgens applied for cancer diagnosis were introduced, including isolated cancer cell imaging, tumor microenvironment-responsive imaging, biological process-activated imaging, and tumor tissue-localized imaging. Then TM-AIEgens used for different types of image-guided therapy were presented, including chemotherapy, photodynamic therapy (PDT), photothermal therapy (PTT), radiotherapy, and combination therapy. For each example, we focused on the structure design, the generation mechanism of AIE activity, and the diagnostic or theranostic performance. At last, we discussed the current challenges and opportunities for TM-AIEgens. This review gives a comprehensive landscape of TM-AIEgens in cancer diagnosis and theranostics and will engage more researchers to devote their efforts to this area.