Tuning the Aggregation of Gold Nanoparticles prepared by Laser Ablation with Halide Salt

Gold nanoparticles (NPs) have been largely studied due to their surface plasmon resonance properties that are strongly dependent on size, shape and coupling effects between NPs as well as their dispersive medium [1,2]. Thanks to their unique optical properties, gold NPs and their aggregates are applied in different fields like medicine [3], energy [1] and sensing [4]. Here, we studied the surface plasmon resonance properties of strongly coupled gold NPs obtained by “in water” laser ablation and aggregated by adding potassium bromide. Unlike other classical chemical synthesis methods of nanoparticles, laser ablation in liquids provides a unique way to obtain surface-clean and ligand-free nanoparticles, ready to be used [5]. The aggregation of gold NPs was analysed under different experimental conditions such as salt concentration, temperature and laser irradiation. The extinction spectra (figure 1a) show two peaks which red-shifted by increasing salt concentration. Supported by Finite-Difference-Time-Domain simulations we can hypothesize the formation of small nanoparticle chains which became longer by increasing potassium bromide concentration as also demonstrated by electron microscope data. Figure 1b shows the effect of temperature on the aggregation process which seems to be suppressed at higher temperatures