Gold nanorods-conjugated TiO2 nanoclusters for the synergistic combination of phototherapeutic treatments of cancer cells

BACKGROUND

Recently, a combination of photodynamic therapy (PDT) and photothermal therapy (PTT) to generate reactive oxygen species (ROS) and heat to kill cancer cells, respectively has attracted considerable attention because it gives synergistic effects on the cancer treatment by utilizing the radiation of nontoxic low-energy photons such as long wavelength visible light and near IR (NIR) penetrating into subcutaneous region. For the effective combination of the phototherapies, various organic photosensitizer-conjugated gold nanocomplexes have been developed, but they have still some disadvantages due to photobleaching and unnecessary energy transfer of the organic photosensitizers.

RESULTS

In this study, we fabricated novel inorganic phototherapeutic nanocomplexes (Au NR-TiO2 NCs) by conjugating gold nanorods (Au NRs) with defective TiO2 nanoparticle clusters (d-TiO2 NP clusters) and characterized their optical and photothermal properties. They were observed to absorb a broad range of visible light and near IR (NIR) from 500 to 1000 nm, exhibiting the generation of ROS as well as the photothermal effect for the simultaneous application of PDT and PTT. The resultant combination of PDT and PTT treatments of HeLa cells incubated with the nanocomplexes caused a synergistic increase in the cell death compared to the single treatment.

CONCLUSION

The higher efficacy of cell death by the combination of PDT and PTT treatments with the nanocomplexes is likely attributed to the increases of ROS generation from the TiO2 NCs with the aid of local surface plasma resonance (LSPR)-induced hot electrons and heat generation from Au NRs, suggesting that Au NR-TiO2 NCs are promising nanomaterials for the in vivo combinatorial phototherapy of cancer.

Size-selected TiO₂ nanocluster catalysts for efficient photoelectrochemical water splitting

Nanoclusters (NCs) are of great interest because they provide the link between the distinct behavior of atoms and nanoparticles and that of bulk materials. Here, we report precisely controlled deposition of size-selected TiO2 NCs produced by gas-phase aggregation in a special magnetron sputtering system. Carefully optimized aggregation length and Ar gas flow are used to control the size distribution, while a quadrupole mass filter provides precise in situ size selection (from 2 to 15 nm). Transmission electron microscopy studies reveal that NCs larger than a critical size (∼8 nm) have a crystalline core with an amorphous shell, while those smaller than the critical size are all amorphous. The TiO2 NCs so produced exhibit remarkable photoelectrochemical water splitting performance in spite of a small amount of material loading. NCs of three different sizes (4, 6, and 8 nm) deposited on H-terminated Si(100) substrates are tested for the photoelectrochemical catalytic performance, and significant enhancement in photocurrent density (0.8 mA/cm(2)) with decreasing NC size is observed with a low saturation voltage of -0.22 V vs Ag/AgCl (0.78 V vs RHE). The enhanced photoconductivity could be attributed to the increase in the specific surface area and increase in the number of active (defect) sites in the amorphous NCs. The unique advantages of the present technique will be further exploited to develop applications based on tunable, size-selected NCs.