The Influence of Alkanethiols on the Production of Hydrophobic Gold Nanoparticles via Pulsed Laser Ablation in Liquids

The ability to suspend plasmonic metal nanoparticles in apolar environments is crucial for leveraging their optical properties in amphiphilic biological settings. Pulsed Laser Ablation in Liquids (PLAL) is a well-known technique for producing gold nanoparticles (AuNPs) in aqueous environments. However, ablation in organic liquids for synthesizing hydrophobic AuNPs still presents challenges, particularly regarding the relationship between colloidal stability and the ligand shell. In this study, hydrophobic AuNPs were generated by PLAL of gold in a 1-alkanethiol/n-decane solution and further processed with laser fragmentation. The results showed that longer chain length alkanethiols (ATs) led to smaller average particle sizes; however, there was no significant correlation between AT concentration and particle size. Stability was assessed by monitoring changes in the extinction spectra, indicating that lower AT concentrations stabilized the colloids, while higher concentrations led to faster particle aggregation. Moreover, longer chain length ATs exhibited enhanced stability. A secondary irrdadiation was performed to achieve monodisperse nanoparticle distributions with mean sizes around 3 nm. These colloids were indefinetly stable over the range of chain lengths. Vibrational spectroscopy was also used to analyze the AuNP surface chemistry, revealing the presence of oxidized carbon species and graphitic carbon.