Co‐Solvent‐Aided Opto‐Thermophoretic Printing of Gold Nanorod Assemblies

Abstract The controlled deposition of plasmonic nanoparticles on solid surfaces is critical for the fabrication of medical diagnostics, devices, and sensors. Despite recent advances in harnessing thermal gradients to achieve controlled deposition of nanoparticles at a laser spot, the deposition of anisotropic gold nanoparticles by this approach is a challenge in aqueous solution. Herein, the use of ethanol as a co‐solvent is shown to enable rapid (<10 s) and effective deposition of gold nanorods in the presence of polyvinylpyrrolidone on unmodified glass substrates. The influence of key parameters, including polymer concentration and molecular weight, co‐solvent content, nanoparticle concentration, and laser power, is studied. While ethanol content and polymer size have the largest impact on the assembly structure, all have an impact on the assembly growth rate. Polymer size is found to significantly impact the degree of nanorod assembly found in the pattern, which leads to a surface‐enhanced Raman scattering enhancement factor up to 10 ⁸ . In summary, this approach utilizes thermal gradients to direct the formation of highly localized plasmonic assemblies without the need of functionalization of the substrate. This simple, fast, and adaptable approach is a promising platform for the scalable patterning of plasmonic nanostructures.