NIR-light-induced surface-enhanced Raman scattering for detection and photothermal/photodynamic therapy of cancer cells using methylene blue-embedded gold nanorod@SiO2 nanocomposites

Methylene blue-loaded gold nanorod@SiO₂ (MB-GNR@SiO₂) core@shell nanoparticles are synthesized for use in cancer imaging and photothermal/photodynamic dual therapy. For the preparation of GNR@SiO₂ nanoparticles, we found that the silica coating rate of hexadecylcetyltrimethylammonium bromide (CTAB)-capped GNRs is much slower than that of PEGylated GNRs due to the densely coated CTAB bilayer. Encapsulated MB molecules have both monomer and dimer forms that result in an increase in the photosensitizing effect through different photochemical pathways. As a consequence of the excellent plasmonic properties of GNRs at near-infrared (NIR) light, the embedded MB molecules showed NIR light-induced SERS performance with a Raman enhancement factor of 3.0 × 10¹⁰, which is enough for the detection of a single cancer cell. Moreover, the MB-GNR@SiO₂ nanoparticles exhibit a synergistic effect of photodynamic and photothermal therapies of cancer under single-wavelength NIR laser irradiation.