Bimetallic nanoparticles enhance photoactivity of conjugated photosensitizer

Although photodynamic therapy (PDT) of cancer has been continuously improved, its efficiency is still limited by the high toxicity in the absence of irradiation, aggregation and deactivation by biomolecules of the most common photosensitizers (PS). The association of PS to nanoparticles (NPs) can be a promising tool to overcome these limitations and also to enhance PS tumoral selectivity. In addition, the association of PS to metallic NPs may provide the modulation of PS fluorescence and also the enhancement of PS photoactivity due to the electronic coupling with NPs plasmon effect. Adversely to the innumerous work on the coupling of PS to metallic NPs, the application of bimetallic NPs with this goal has not been explored yet. In this work we investigated the physicochemical properties and cytotoxicity of bimetallic gold-platinum NPs (AuPtNPs) conjugated to a chlorin molecule modified with a thiol group. Additionally, chlorin was coupled to AuNPs for comparative purposes since these have been the most commonly used NPs in PDT. The results showed that both platforms promoted the chlorin solubility in water which is crucial in biological applications. Despite the enhancement of photoactivity promoted by both NPs in comparison with chlorin in solution, chlorin-conjugated with AuPtNPs proved to be a more suitable platform for PDT application, since it showed a lower dark citotoxicity, as well as a higher generation of singlet oxygen and cell internalization compared with chlorin-conjugated AuNPs. It is important to highlight that this is the first work reporting on the enhancement of PS photoactivity by its conjugation to AuPtNPs.