Gold nanoparticles functionalized by phosphine oxide derivatives: characterization and influence of ligand structure on their stability

The rapid development of nanotechnology has led to an incredible expansion in the production and use of nanoparticles (NPs). Gold nanoparticles (AuNPs) are one of the most significant types of NPs and have shown outstanding medical applications due to their low toxicity. AuNPs stabilized by phosphine derivatives have extensive applications in sensing, catalysis, and biological imaging. In this work, phosphine oxide ligands were employed to stabilize AuNPs in DMSO with NaBH₄ as the reducing agent. These ligands included (3-thioacetyl-<i>N</i>-ethylmethylamine)-diphenylphosphine oxide (10), (3-thioacetylpropyl)-thiodiphenylphosphine oxide (7), (3-thioacetylpropyl)di-(<i>p</i>-tolyl)phosphine oxide (4A), and (3-thioacetylpropyl)-diphenylphosphine oxide (4B). The AuNPs were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), and UV-Vis spectroscopy. AuNPs stabilized by both 4B and 7 remained stable for five months. However, when 4A and 10 were used, the AuNPs remained stable for three months. Due to their small surface-area-to-volume ratio and good stability, AuNPs are nowadays needed for different applications. Therefore, small, homogenous, and spherical AuNPs were considered herein, where their sizes were 55 ± 13.6 nm, 40 ± 8 nm, 25 ± 6 nm, and 43 ± 7 nm for 4A-AuNPs, 4B-AuNPs, 7-AuNPs, and 10-AuNPs, respectively, based on TEM results. These results aligned with the DLS results, where homogenous AuNPs were produced with no evidence of aggregation.