Role of the Polymeric Matrix and Surface Affinity During Gold Nanoparticles Patterning by Multi-Photon Photo-Reduction

Gold nanoparticles (GNPs) can be patterned on specific positions and substrates by Multi-Photon Direct Laser Writing (MP-DLW) in wet polymeric matrices doped with tetrachloroauric acid (HAuCl₄) as gold precursor. The Hamaker constants describing the GNP-GNP interaction and the interaction between the GNPs and the surrounding materials is described, defining the role of the polymeric matrix; thus, its limits and the advantages are thoroughly analysed. The Multi-Photon Photo-Reduction (MPPR) process, leading to the GNPs creation, triggers a local temperature rising, which can ablate the polymer and influences the particle distribution, size and density. The GNPs polydispersity also depends on the water content in the film, variable because of the vaporization. A protocol to perform MP-DLW of GNPs, without the use of the polymer is illustrated: by treating the surface with a surfactant, it is possible to make the particles stick to the substrate, control their size and reduce the diffusive and convective effects generated by the MPPR.