In a recent article published in the journal Material applied todaythe authors reported a new strategy to directly deposit anatase titanium oxide onto a gold nanobipyramid (Au NBP/a-TiO2) via a low-temperature hydrothermal reaction.
Study: Direct deposition of anatase TiO2 on a thermally unstable gold nanobipyramid: plasmonic nanohybrid with conserved morphology for combined photothermal and photocatalytic cancer therapy. Image credit : Mopic/Shutterstock.com
Being a low temperature strategy, the current method does not affect the substrate morphology. They also performed in vitro and live studies to demonstrate the potency of the synthesized nanohybrid framework in biomedical applications.
TiO2 Hybridization with gold nanostructures
TiO2 is a biocompatible inorganic photomedicine. However, the live application of TiO2 semiconductors is limited due to the large band gap resulting in restricted tissue penetration of ultraviolet (UV) photons and phototoxicity.
Theoretically, hybridization of anatase TiO2 with anisotropic gold nanostructures can be an immediate solution, as it can increase UV-restricted photoactivity to near-infrared (NIR), facilitating tissue penetration. However, the practical implication of this hybridization process is difficult due to the low thermal stability of anisotropic gold nanostructures.
Therefore, subjecting sharp-tipped NBP Au to high-temperature annealing conditions upon hybridization with anatase TiO2 can cause agglomeration and partial melting in Au NBP, thus disturbing its morphology. Therefore, designing a practical strategy to deposit TiO anatase2 on NBP Au pointed without altering the morphology is a challenge.
TiO2– Decorated pointed toe Au NBP
In the present study, researchers applied a low-temperature hydrothermal reaction to hybridize heat-sensitive anisotropic gold nanostructures with crystalline anatase TiO.2. Synthesized TiO2The deposited pointed NBP is a novel framework with intact morphology and colloidal stability.
The working mechanism of synthesized Au NBP/a-TiO2 involves the generation of reactive oxygen species (ROS). The irradiation of NIR light induces an electric field by localized surface plasmon resonance (LSPR) and generates hot electrons on the Au NBP surface.
These generated electrons are then pushed to the conduction band of anatase TiO2 layer. As a result, the adjacent oxygen is reduced to its initial superoxide and final hydroxyl radicals. Thus, demonstrating the effectiveness of the new Au NBP/a-TiO2 as a powerful tool for combined photodynamic/photothermal cancer therapy.
The morphology and properties of the novel nanostructure were confirmed using transmission electron microscopy (TEM), energy dispersive X-rays (EXD), selected region electron diffraction (SAED), X-ray diffraction (XRD), surface plasmon resonance (SPR). the live and in vitro studies conducted have determined its potential in biomedical application.
The results of TEM analysis confirmed the sharp morphology of Au NBP and the surface presence of TiO2 nanoclusters in Au NBP/a-TiO2. While EXD elemental mapping revealed the distribution of gold nucleus and peripheral titanium, SAED and XRD measurements confirmed the formation of the anatase phase. Moreover, the intense SPR peaks of AuNBP/a-TiO2 were on par with plasmonic Au NBP, indicating the influence of the plasmonic form of Au NBP/a-TiO2 on the optical properties.
The photothermal activity was confirmed by the dispersion in water of Au NBP/a-TiO2 and its corresponding temperature rise to 57 degrees Celsius upon NIR irradiation. Submit To NBP/a-TiO2 repeated cycles of heating and cooling using an 808 nanometer laser revealed its structural stability.
In addition, the photocatalytic activity of Au NBP/a-TiO2 was confirmed by free radical oxygen species (ROS) generation and subsequent rhodamine B (RhB) photobleaching under NIR irradiation at 808 nanometers for 24 hours. Additionally, the hydroethidine probe confirmed the generation of superoxide and the electromagnetic radiation confirmed the hydroxyl radical.
Nanohybridization in Au NBP/a-TiO2 enhanced generation of NIR-stimulated ROS, demonstrating its potential applicability in photodynamic cancer therapy.
Human glioblastoma or U-87 MG cells were used to observe the in vitro anticancer activity of the new framework when subjected to NIR irradiation. The researchers observed that Au NBP/a-TiO2 showed strong and localized diffusion signals at the intracellular level, revealing the consumption of TiO2– gold nanomaterials deposited by U-87 MG cells.
Cytotoxicity was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) test with and without NIR irradiation at 808 nanometers revealed than Au NBP/a-TiO2 treated cells remained unchanged up to a gold dose of 23 micrograms per milliliter in the absence of NIR irradiation. However, the same treated cells exposed to NIR exhibited moderate to severe phototoxicity.
Phototherapy performed on mice injected with Au NBP/a-TiO2– containing U-87 MG cells revealed that in the absence of light, the mice showed no anticancer activity, while the same NIR irradiation at 808 nanometers for five minutes revealed significant anticancer activity.
The reason for this activity is attributed to the combined contribution of Au NBP and the generation of NIR-activated photocatalytic ROS.
In conclusion, the new nano Au NBP/a-TiO framework2 synthesized in this study has promising applications in the photothermal/photodynamic treatment of cancer. In addition, the low temperature hydrothermal strategy contributed to the direct deposition of crystalline anatase TiO2 on Au NBP, retaining the pointed morphology of the auriferous surface.
When subjected to NIR irradiation, the gold core of AuNBP/a-TiO2 produces hot electrons, which are directly transferred into the conduction band of TiO2 revealing NIR-induced photocatalytic activity. Moreover, retention of plasmonic morphology in Au NBP/a-TiO2 exhibited photothermal effect under NIR irradiation
the live and in vitro studies in U-87 MG treated with NBP/a-TiO2 containing mice revealed its potential in combined photothermal and photodynamic cancer therapy. Thus, the novel nanostructure may be ideal for NIR-sensitive photocatalytic hybrid nanostructures.
Jang, D., Yu, S., Chung, K., Yoo, J., Mota, F., Wang, J., Ahn, D., Kim, S. and Kim, D., 2022. Direct deposit from anatase TiO2 on thermally unstable gold nanobipyramide: plasmonic nanohybrid with conserved morphology for combined photothermal and photocatalytic cancer therapy. Materials applied today, 27, p.101472. https://www.sciencedirect.com/science/article/pii/S2352940722001068.