PEG-NHCs as surface ligands for Au nanomaterials have shown increased stabilizing performance in various biomedically relevant conditions, including buffer solutions of a wide range of pH values, oxidative conditions, and the exchange with exogenous natural and PEG-based thiols (PEG-SH). In this study, AuNP-3 were exposed to a series of conditions and retained colloidal stability in aq. media and easy handling in various organic solvents. In terms of biologically relevant conditions, AuNP-3 were dispersed in 1×PBS (a common physiological buffer), 0.6 M NaCl (a high ion solution), HCl solution (pH 2), NaOH solution (pH 12), 1 M H2O2 (an oxidative environment), fetal bovine serum (FBS, a complex media for cell culture) and 3 mM glutathione (GHS, a model system for natural occurring thiols). Monitoring the SP band of AuNP-3 over a period up to 7 days revealed minimal to no changes in most of these conditions, showing retained colloidal stability on par with previously published systems (for UV-Vis spectra see ESI; Figure ). Interestingly, AuNP-3 show a sharpening of the SP band while exposed to H2O, 1×PBS, and NaCl (0.6 M) over the course of 7 days, indicating the slow dispersion of small aggregates caused by previous in vacuo drying steps or rearrangement of surface-bond PEG chains. AuNP-3 exposed to 3 mM PEG-SH (Mn=2000 g/mol) show a red shift (∆nm ~3 nm) and peak broadening.