Biocompatible triplex Ag@SiO2@mTiO2 core-shell nanoparticles for simultaneous fluorescence-SERS bimodal imaging and drug delivery.

Herein, we report the synthesis of biocompatible triplex Ag@SiO(2)@mTiO(2) core-shell nanoparticles (NPs) for simultaneous fluorescence-surface-enhanced Raman scattering (F-SERS) bimodal imaging and drug delivery. Stable Raman signals were created by typical SERS tags that were composed of Ag NPs for optical enhancement, a reporter molecule of 4-mercaptopyridine (4-Mpy) for a spectroscopic signature, and a silica shell for protection. A further coating of mesoporous titania (mTiO(2)) on the SERS tags offered high loading capacity for a fluorescence dye (flavin mononucleotide) and an anti-cancer drug (doxorubicin (DOX)), thereby endowing the material with fluorescence-imaging and therapeutic functions. The as-prepared F-SERS dots exhibited strong fluorescence when excited by light at 460 nm whilst a stable, characteristic 4-Mpy SERS signal was detected when the excitation wavelength was changed to longer wavelength (632.8 nm), both in solution and after incorporation inside living cells. Their excellent biocompatibility was demonstrated by low cytotoxicity against MCF-7 cells, even at a high concentration of 100 μg  mL(-1). In vitro cell cytotoxicity confirmed that DOX-loaded F-SERS dots had a comparable or even greater therapeutic effect compared with the free drug, owing to the increased cell-uptake, which was attributed to the possible endocytosis mechanism of the NPs. To the best of our knowledge, this is the first proof-of-concept investigation on a multifunctional nanomedicine that possessed a combined capacity for fast and multiplexed F-SERS labeling as well as drug-loading for cancer therapy.