One-Step Synthesis of PEG-Functionalized Gold Nanoparticles: Impact of Low Precursor Concentrations on Physicochemical Properties

Polyethylene glycol-capped gold nanoparticles (PEG-AuNPs) are highly promising for biological and medical applications due to their biocompatibility, enhanced stability, and low cytotoxicity. The successful synthesis method presented here was a one-step process where both reduction and functionalization took place simultaneously using lower concentrations of gold precursors. Unlike previous methods that used higher concentrations (> 10 mM) and did not explore varying molar ratios, this study investigates the physicochemical properties of PEG-AuNPs synthesized with precursor concentrations ranging from 0.5 mM to 5 mM. Transmission electron microscopy images revealed an increase in the particle sizes of spherical nanoparticles from 14.5nm to 46.7nm as the precursor concentration increased, consistent with dynamic light scattering measurements. UV-Vis spectroscopy confirmed that spherical nanoparticles were formed having surface plasmon resonance peaks ranging from 520–530 nm. Fourier transform infrared spectroscopy analyses revealed the interactions between PEG ligands and gold nanoparticles where some specific peaks exist around 1632cm-1 while the O-H stretching peak shifted from approximately 3400 cm-1 to about 3490 cm-1, confirming successful surface modification. Photoluminescence spectroscopy revealed maximum emission particularly observed at the lowest precursor concentration (0.5 mM). Importantly, the synthesized PEG-AuNPs even at the lowest precursor concentration of 0.5mM demonstrated exceptional stability in saline conditions, maintaining dispersion even in the presence of 500 mM NaCl. This one-step synthesis method at reduced precursor concentrations not only enables precise control over the nanoparticles’ size and optical properties but also enhances their stability and tunable fluorescence. These findings present a scalable and versatile approach for the tailored synthesis of PEG-AuNPs, making them suitable for advanced biological and medical sensing applications.