Anti-photobleaching cyanine-based nanoparticles with simultaneous PET and ACQ effects for improved tumor photothermal therapy

To design anti-photobleaching photothermal agents (PTAs) is of great significance for tumor photothermal therapy (PTT). Heptamethine cyanine (Cy7) dyes as one of near-infrared (NIR) PTAs has received extensive attention in PTT. But the poor photostability of Cy7 dyes severely restrict their clinical application. Herein, two new Cy7 dyes DTZCy and WTZCy were prepared, which showed better anti-photobleaching performance than ICG, a commercial Cy7 dye proved by FDA. Noteworthily, the contributions of quenching fluorescence and enhancing photostability to improving the photothermal conversion efficiency (PCE) of Cy7-based PTAs were discussed. DTZCy exhibited much better PCE (η = 31.8%) than WTZCy (η = 16.5%) due to the increased photostability caused by the intramolecular photoinduced electron transfer (PET) effect. Silica nanoparticles encapsulating DTZCy, named as DTZCy@SiO2 NPs, displayed higher PCE (η = 34.6%) and satisfying photothermal stability both in vitro and vivo, which was attributed to the improved anti-photobleached ability caused by aggregation-caused quenching (ACQ) mechanism. This work may provide new strategies for constructing anti-photobleaching PTAs by simultaneously employing PET and ACQ mechanisms to achieve efficient tumor PTT.