Gold Nanoparticles Core Size Effect in Interactions with Humic Substances

The current study investigates the role of nanoparticle core size effect in interactions of gold nanoparticles with humic acid. The discharge of diagnostic imaging gold nanoparticles into surface waters from clinical effluents presents potential for their interactions with aquatic organisms and environmental entities such as humic substances. Therefore, it is critical to understand the interactions of gold nanoparticles with natural organic matter (humic substances), to gain insight into the fate and transport of these particles in aquatic systems. The current study employed dynamic light scattering to investigate the changes in zeta potential and hydrodynamic size of citrate-coated gold nanoparticles (CT-GNPs) with core sizes 10 and 50 nm, in the presence of commercial humic acid (HA) having concentration 2 ppm. Humic acid controls at the same concentration exhibited micron sized aggregates when titrated in the pH range of 1-12, however the humic acid aggregates were absent when the CT-GNPs + HA mixture was titrated in the same pH range, suggesting disaggregation of humic acid aggregates. The zeta potential data for CT-GNPs with core size 50 nm indicated modification of surface properties in the presence of humic acid however, for CT-GNPs with core size 10 nm the zeta potential did not change significantly in the presence of HA. The overall results suggested that the CT-GNPs facilitated disaggregation of humic acid aggregates and the nanoparticle core size does affect the interactions with humic acids. The CT-GNPs with core size 50 nm were well stabilized with humic acid as compared to the 10 nm particles under environmental conditions.