Synthesis of Bi2WO6-x nanodots with oxygen vacancies as all-in-one nanoagent for simultaneous CT/IR imaging and photothermal/photodynamic therapy of tumors

All-in-one nanoagents with single-component and all-required functions have attracted increasing attention for the imaging-guided therapy of tumors, but the design and preparation of such nanoagents remains a challenge. Herein, we report the introduction of oxygen vacancies to traditional semiconductors with heavy-metal elements for tuning photoabsorption in near infrared (NIR) region, by using Bi2WO6 (band-gap: ~2.7 eV) as a model. Bi2WO6-x nanodots with sizes of ~3 or ~8 nm have been prepared by a facile coprecipitation-solvothermal method assisted with citric acid (CA, 0.1-1.5 g) as the reduction agent. CA confers the removal of O atoms from [Bi2O2]2+ layer during solvothermal process, resulting in the formation of plenty of oxygen vacancies in Bi2WO6-x crystal. As a result, NIR photoabsorption of Bi2WO6-x nanodots can be remarkably enhanced with the increase of CA amount from 0 to 1.0 g. Under the irradiation of single-wavelength (808-nm, 1.0 W cm-2) NIR laser, black Bi2WO6-x-CA1.0 nanodots can not only efficiently produce sufficient amount of heat with photothermal conversion efficiency of 45.1% for photothermal therapy, but also generate singlet oxygen (1O2) for photodynamic therapy. Furthermore, due to heavy-metal (Bi and W) elements, Bi2WO6-x-CA1.0 nanodots have high X-ray attenuation ability for CT imaging. After Bi2WO6-x-CA1.0 nanodot dispersion is injected to the tumor-bearing mice, the tumor can be imaged by CT and IR thermal camera. After the irradiation by single-wavelength (808-nm, 1.0 W cm-2, 10 min) NIR laser, the tumor can be completely suppressed by the synergic photothermal and photodynamic effects of Bi2WO6-x-CA1.0 nanodots, without recurrence and treatment-induced toxicity. Therefore, Bi2WO6-x nanodots have great potential as a novel all-in-one nanoagent for the imaging and phototherapy of tumors.