Magnetic nanocubes, with a controlled precursor molar concentration of ferric nitrate fixed at 0.004 M to ferrous chloride ranging from 0.002 to 0.01 M, were synthesized by a new simple colloidal method at 60 °C under 1 M alkaline condition. The metallic Au-ultrathin layer was successfully functionalized on the magnetic nanocubes surface for the fabrication of the core–shell structure (Fe₃O₄@Au) by the borohydrate reduction of HAuCl₄ in water/poly-L-histidine solution. The functionalized core–shell structure with varying molar-ratios of Fe³⁺/Fe²⁺ in aqueous media, core–shell structural characteristics (for example, size, morphology, and shell thickness), and physical properties (for example, crystalline, electronic, optical, and magnetic ones) of the resultant functional nanocubes were systematically investigated using UV-visible spectroscopy, SEM, TEM, XRD, XPS, EDX, and superconducting quantum interface device (SQUID) magnetometer analysis. The core–shell structure of Fe₃O₄@Au exhibits plasmonic properties with high magnetization and showed excellent hyperthermia-photothemal activity towards the cancer cell (HeLa) killing. For the hyperthermia killing of cancer cells under the alternating current magnetic field (AMF), the as-prepared Fe₃O₄ exhibited higher activity than the Fe₃O₄@Au nanoparticles. Interestingly, under the simultaneously combined AMF and photoirradiation with Fe₃O₄@Au, much higher cancer cell killing was found than with only AMF induced hyperthermia killing. The promoting effect of an Au-ultrathin shell supported on Fe₃O₄ showed strong absorption in the visible region due to localized surface plasmon resonance and increased the hyperthermia-photothermal temperature with the photothermal stability of the Fe₃O₄@Au nanoparticles, rather than only Fe₃O₄. It was found that the cell killing activity depends on the optical and magnetic properties of the Fe₃O₄@Au nanocubes. The optical and magnetic properties depended on the molar-concentration ratios of precursors of Fe(NO₃)₃·9H₂O and FeCl₂·4H₂O. The synthesized Fe₃O₄@Au nanocubes have great potential for a combination of cancer imaging and local treatment as a cancer cell killing paradigm of “see and treat” applications.

Fe-doped TiO₂ nanopowders with controlled molar-atomic ratios of iron to titanium oxide (in percentage) ranging from nominal 1 to 10% were synthesized by a new simple sol–gel method. Metallic Ag nanoparticles were successfully deposited on the nanopowder of the Fe-doped TiO₂ surface by citrate reduction of AgNO₃ in water/CH₃CN mixture. The molar ratio of iron to TiO₂ , phase formation, bandgaps, crystallinity, catalytic and plasmonic properties of the resultant composites were systematically investigated using UV-visible spectroscopy, SEM, TEM, XRD, XPS, EDX, and photoluminescence spectral analyses. The photocatalytic activity of Ag@Fe-doped TiO₂ composite nanoclusters was evaluated through photocatalytic killing of cancer cells. For the photocatalytic killing of cancer cells under visible light irradiation, as-prepared Ag@Fe-doped TiO₂ nanopowders exhibited higher activity than Fe-doped TiO₂ . The promoting effect of the Ag nanoparticles deposited on the Fe-doped TiO₂ surface showed strong absorption in the visible region due to localized surface plasmon resonance of Ag and inhibited the recombination of photoelectrons and holes rather than only Fe-doped TiO₂ . The cytotoxic cell killing efficiency depends on the molar ratio of Fe content to TiO₂ . The optimum Fe content in Fe-doped TiO₂ was determined to be 5% due to the Fe/TiO₂ molar ratio. Based on the obtained results, a plausible mechanism was also proposed.

The photocatalytic and plasmonic photothermal cancer cell-killing activity of the metallic Au-capped TiO₂ (Au@TiO₂ ) composite colloidal nanopellets has been investigated on HeLa cells under UV-visible (350–600 nm) light irradiation. The Au@TiO₂ composite nanopellets with the uniform Au-capped TiO₂ structure were successfully synthesized by simple reduction of HAuCl₄ on the surface of TiO₂ nanoparticles. The morphological structure and surface properties of Au@TiO₂ were characterized by using UV-visible absorption spectroscopy, TEM, SEM, XPS, EDX and XRD analyses. The formation of hydroxyl radicals (˙OH) was confirmed by photoluminescence (PL) spectra. The photocatalytic and photothermal cell-killing activity of the Au@TiO₂ nanopellets was found to vary with the molar ratio of Au to TiO₂ . The direct involvement of the metal particles in mediating the electron transfer from the photoexcited TiO₂ under the band gap excitation is considered to carry out the efficient photocatalytic reaction on the cells. The plasmonic absorption spectra of Au@TiO₂ suspensions were also measured for the evaluation of photothermal cell killing. The charge separation, the interfacial charge-transfer and photothermal activity promoted the photocatalytic–photothermal cancer-cell killing more than TiO₂ alone. The cytotoxic effect of Au@TiO₂ nanopellets with low concentration of gold (TiO₂ : Au molar ratio > 1 : 1) was found to be 100%, whereas that of the commercial TiO₂ (P25) was ca. 50%. The comparative study of the cell viability using Au alone and TiO₂ alone revealed that the synergistic effect of photocatalytic hydroxyl radical formation and Au-plasmonic photothermal heat generation plays a vital role in the cancer cell killing. A plausible mechanism was also proposed for photocatalytic cancer cell killing based on the obtained results.

Gold colloidal nanoparticles were prepared by the liquid laser ablation of a gold metal plate in water and also by the citrate reduction of HAuCl₄·4H₂O. The gold colloidal nanoparticles with the plasmonic band strongly absorb light, which is converted to the photothermal energy. This photothermal energy gives a cytotoxic effect on epithelial carcinoma cells. Interestingly, we found that the size and shape of the nanoparticles are changed by light during the photothermal process in vitro. The cervical carcinoma cell line (HeLa cell) was incubated with the colloidal gold nanoparticles and then exposed to continuous visible light at 400–600 nm with UV- and heat-cutoff filters. The distinct cell-killing effect was observed by this procedure. In the absence of the gold colloidal nanoparticles, only a small amount of cells were photothermally destroyed.