Impact of Quantum Dot Surface on Complex Formation with Chlorin e6 and Photodynamic Therapy

Nanomaterials have permeated various fields of scientific research, including that of biomedicine, as alternatives for disease diagnosis and therapy. Among different structures, quantum dots (QDs) have distinctive physico-chemical properties sought after in cancer research and eradication. Within the context of cancer therapy, QDs serve the role of transporters and energy donors to photodynamic therapy (PDT) drugs, extending the applicability and efficiency of classic PDT. In contrast to conventional PDT agents, QDs’ surface can be designed to promote cellular targeting and internalization, while their spectral properties enable better light harvesting and deep-tissue use. Here, we investigate the possibility of complex formation between different amphiphilic coating bearing QDs and photosensitizer chlorin e6 (Ce6). We show that complex formation dynamics are dependent on the type of coating—phospholipids or amphiphilic polymers—as well as on the surface charge of QDs. Förster’s resonant energy transfer occurred in every complex studied, confirming the possibility of indirect Ce6 excitation. Nonetheless, in vitro PDT activity was restricted only to negative charge bearing QD-Ce6 complexes, correlating with better accumulation in cancer cells. Overall, these findings help to better design such and similar complexes, as gained insights can be straightforwardly translated to other types of nanostructures—expanding the palette of possible therapeutic agents for cancer therapy.