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 520-530nm. 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.