Strain-Modulated Seeded Growth of Highly Branched Black Au Superparticles for Efficient Photothermal Conversion

Creating highly branched plasmonic superparticles can effectively induce broadband light absorption and convert light to heat regardless of the light wavelength, angle, and polarization. However, their direct synthesis in a controllable manner remains a significant challenge. In this work, we propose a strain modulation strategy to produce branched Au nanostructures that promotes the growth of Au on Au seeds in the Volmer–Weber (island) mode instead of the typical Frank–van der Merwe (layer-by-layer) mode. The key to this strategy is to continuously deposit polydopamine formed in situ on the growing surface of the seeds to increase the chemical potential of the subsequent deposition of Au, thus achieving continuous heterogeneous nucleation and growth. The branched Au superparticles exhibit a photothermal conversion efficiency of 91.0% thanks to their small scattering cross-section and direction-independent absorption. Even at a low light power of 0.5 W/cm2 and a low dosage of 25 ppm, these particles show an excellent efficacy in photothermal cancer therapy. This work provides the fundamental basis for designing branched plasmonic nanostructures and expands the application scope of the plasmonic photothermal effect.