Laser beam controlled drug release from Ce6–gold nanorod composites in living cells: a FLIM study

A new method to image drug release from drug–nanoparticle composites in living cells was established. The composites of silica coated gold nanorods (AuNR@SiO2) and chlorine e6 (Ce6) photosensitizers (AuNR@SiO2–Ce6) were formed by electrostatic force with a Ce6 loading efficiency of 80%. The strong resonance absorptions of AuNR@SiO2–Ce6 in the near-infrared (NIR) region enabled the effective release of Ce6 from AuNR@SiO2–Ce6 by 780 nm CW laser irradiation. The 780 nm laser beam was applied to not only control the releasing amount of Ce6 from cellular AuNR@SiO2–Ce6 by adjusting the irradiation dose (time), but also to spatially confine the Ce6 release in cells by focusing the laser beam on the target sites. Furthermore, the fluorescence lifetime of Ce6 was found to change drastically from 0.9 ns in the AuNR@SiO2–Ce6 complex to 6 ns after release, and therefore fluorescence lifetime imaging microscopy (FLIM) was introduced to image the photo-induced Ce6 release in living cells. Finally, the controllable killing effect of photodynamic cancer therapy (PDT) using AuNR@SiO2–Ce6 was demonstrated by changing the released amount of Ce6, which indicates that AuNR@SiO2–Ce6 is promising for targeted tumour PDT.