Spectral drifts in surface textured Fe3O4-Au, core– shell nanoparticles enhance spectra-selective photothermal heating and scatter imaging

We report a significant spectral drift (up to 110 nm) between optical scattering and extinction in magnetite-
gold (Fe3O4-Au) core–shell nanostructures. The drift was observed experimentally using single-particle
broadband dark-field scattering microspectroscopy and solution extinction experiments. Infrared
thermography demonstrates an enhanced photothermal activity of these nanoparticles at extinction
wavelengths that are far drifted from the wavelengths that produce the best results for imaging via scattering.
For example, a relatively smooth gold shell leads to 19% more photothermal activity at 532 nm compared
to 690 nm whereas a rough-texture, popcorn type morphology gold shell with three times higher
drift, is 170% more efficient at 532 nm. We suggest that the enhanced photothermal response results
directly from a reduced competition between absorption and scattering as a consequence of the spectral
drift. This spectral drift can be advantageous in multimodal theranostics where therapy and imaging are
performed independently at different wavelengths