Confined structure regulations of molybdenum oxides for efficient tumor photothermal therapy

Molybdenum oxide nanoparticles (NPs) with tunable plasmonic resonance in the near-infrared region display superior semiconducting features and photothermal properties, which are highly related to the crystalline and defective structures such as oxygen deficiencies. However, fundamental understanding on the structure-function relationship between crystalline/defective structures and photothermal properties is still unclear. To address this, herein, we have developed an “in-situ confined oxidation-reduction” strategy to regulate the defect features of molybdenum oxide NPs in the dual-mesoporous silica nanoreactor. Especially, the effects of crystalline structure/oxygen defects of molybdenum oxides on the photothermal performances were investigated by facilely tuning the amount of molybdenum resource and the reduction temperature. As a photothermal nanoagent, the optimal defective molybdenum oxide NPs encapsulated in PEGylated porous silica nanoreactor (designated as MoO_3−x@PPSNs) exhibit excellent biological stability and strong localized surface plasmon resonance effect in near-infrared absorption range with the highest photothermal conversion efficiency up to 78.7% under 808 nm laser irradiation. More importantly, the remarkable photothermal effects of MoO_3−xPPSNs were comprehensively demonstrated both in vitro and in vivo. Consequently, we envision that the plasmonic MoO_3−x NPs in a biocompatible porous silica nano-reactor could be used as an efficient photothermal therapy agent for photothermal ablation of tumors.