Peg sh

Nanoparticles were synthesized based on previously described methods using conventional fabrication procedures [5 (link), 7 (link)]. Briefly, 2 mM hydrogen tetrachloroaurate (III) trihydrate (HAuCl₄:3H₂O, Sigma Aldrich) and 1 mM sodium thiosulfate (Na₂S₂O₃, Sigma Aldrich) were prepared in Milli-Q water in amber bottles and allowed to age for 3 days prior to synthesis. Na₂S₂O₃ was added to the HAuCl₄ in a round bottom flask under mild stirring at room temperature (25 °C) and allowed to react for 1 h at a volumetric ratio of 1.03:1, forming the GGS NP. For temperature studies, the nanoparticles were similarly prepared but stirring occurred on either a hot plate (50 °C), under refrigeration (4 °C), or on ice (0 °C). All nanoparticle samples were centrifuged twice at 3200 g for 40 min, and pellets were resuspended in H₂O to a final optical density (OD) of 1.3. Particles were PEGylated by mixing 1 mL of 250 mM PEG-SH (Laysan Bio 2000 MW) in ultrapure water with 9 mL of the nanoparticle suspension on ice, followed by constant agitation overnight at 4 °C (Rotoflex). PEGylated particles were centrifuged at 3200 g for 40 min at 10 °C to remove excess PEG and were stored in the refrigerator at 4 °C until further use.