Photodynamic inheritance from methylene blue to carbon dots against reduction, aggregation, and DNA interference

Photodynamic therapy (PDT) is a treatment that uses light-sensitive drugs and a light source to destroy cancer cells. Methylene blue (MB) is an efficient photosensitizing agent that has been widely used in PDT. However, MB suffers from the hypochromic effect that is caused by self-aggregation and DNA binding in vivo. It is also easily reduced to ineffective leucomethylene blue in the hypoxic environments surrounding solid tumors. In this work, we prepared MB carbon dots (MB-CDs) using MB as the carbon source. The MB-CDs not only inherit the PDT capabilities of MB, but also demonstrate good biocompatibility and low toxicity. Importantly, MB-CDs demonstrate excellent resistance to interference from reduction, aggregation, and DNA interactions. The MB-CDs exhibited satisfactory PDT activities both in vitro and in vivo. The tumor sizes were reduced to below 20% of their original volumes when irradiated by a 590-nm light-emitting diode source.