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Photodynamic therapy (PDT) is a non-invasive therapy with many advantages over other therapeutic methods, but it is restricted to treat superficial cancers due to the shallow tissue penetration of visible light. The biological window in the near infrared region (NIR) offers hope to extend the penetration depth, but there is no natural NIR excited photosensitizer. Here, we report a novel photosensitizer: NaYbF nanoparticles (NPs). By using a 1,3-diphenylisobenzofuran (DPBF) sensor, we show that the Yb ions can absorb the NIR light and transfer energy directly to oxygen to generate reactive oxygen species (ROS). The efficiency of transferring energy to oxygen by NaYbF NPs is comparable to that of traditional photosensitizers. We have carried out PDT both in vitro and in vivo based on NaYbF NPs; the results demonstrate that NaYbF NPs are indeed an effective NIR photosensitizer, which can help extend the application of PDT to solid tumors owing to the much deeper penetration depth of NIR light.

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This study was conducted to develop a two-stage process for the treatment of Hong Kong leachate. The leachate, containing 4750 mg l-1 of chemical oxygen demand (COD) and 1310 mg l-1 of ammoniacal nitrogen (NH3-N), was first treated in a UASB (upflow anaerobic sludge blanket) reactor at 37 degrees C. The process removed on average 66.1% of COD with 6.1 days of hydraulic retention time (HRT), corresponding to an organic loading rate of 0.78 g-COD (l.day)-1. The UASB effluent, which had an average pH of 8.9, COD of 1610 mg l-1 and NH3-N of 1480 mg l-1, was then further treated by electrochemical oxidation in a batch reactor with recirculation. With the addition of 2000 mg l-1 of chloride (in the form of sodium chloride) and at a current density of 32.3 mA cm-2, 87% of COD and 100% of NH3-N were removed from the UASB effluent in six hours. The energy consumption was < 55 kWh kg-COD-1. The final effluent contained no residual NH3-N and only 209 mg l-1 of COD.