Dual-core Ag/TiO₂ nanoparticles for photothermal therapy

In photothermal therapy, the controlled release of heat by properly synthesized nanomaterials can be assisted by local temperature detection, provided by so-called nanothermometers present near nanoheaters.

The current research study offers various methodologies for measuring local temperature based on the electrical, mechanical or optical properties of materials, like Scanning Thermal Microscopy, Atomic Force Microscopy, Infrared or Fluorescence Thermography and Raman Spectroscopy. In this context, Raman Spectroscopy is a non-contact technique offering high spatial and thermal resolution, which is extremely important for photothermal therapy. Raman signals can be enhanced by exploiting the vicinity of Raman-active materials/molecules to plasmonic nanosystems, which are also widely used to produce nanoheaters.

In this work, composite nanoparticles are specifically developed to provide close contact between plasmonic nanosystems, acting as nanoheaters, and local temperature sensors: silver nanoparticles (AgNP) are surrounded by a shell of anatase titanium dioxide (TiO₂), which has already been tested as a Raman thermometer.

The synthesis is a multi-step process. Silver cores are prepared through a two-pot reaction. First, the silver precursor (AgNO₃) is reduced and stabilized to produce a seed suspension with an average particle size of 7 (± 2) nm. Then, a growth step is performed to reach nanoparticle sizes of 46 (± 8) nm. Dioxide shell formation is carried out using a sol–gel method starting from an ethanol solution of titanium tetrabutoxide (TTB) as a precursor. A final hydrothermal treatment induces the crystallization of TiO₂ to the anatase form.

The resulting nanocomposites are characterized using various techniques, including Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV/Vis extinction and Raman Spectroscopy.

This work demonstrates the feasibility of fabricating nanocomposite structures with high potential as photothermal systems, providing a starting point for future improvements in this field.