It seems that the aggregation process occurs slower than in other samples. AuNP agglomeration and interaction with medium over time was also confirmed with TEM analysis. Differences in the structure of the PBH capping agents used in this study led to distinct associations between individual AuNPs and their environment. The stability of Au[(Gly-Tyr-TrCys)2B] and Au[(Gly-Tyr-Met)2B] differed in cell culture conditions. This difference could be attributed to the stabilising effect of the TrCys group in comparison with the Met group. TrCys and Met residues

are involved in binding to the gold surface. The higher binding of the PBH (Gly-Tyr-TrCys)2B to the gold in comparison with the PBH (Gly-Tyr-Met)2B is due to the additional aromatic interactions of the TrCys residue. The bulkier group, TrCys, may contribute to protecting individual NPs from GANT61 molecular weight assembling into larger agglomerates, thereby leading to the stability of Au[(Gly-Tyr-TrCys)2B] agglomerates. In addition, as revealed by elemental analysis, Au[(Gly-Tyr-TrCys)2B] was stabilised by 40 PBH units in comparison with 7 PBH units for Au[(Gly-Tyr-Met)2B]. Similar considerations can be made for Au[(TrCys)2B] and Au[(Met)2B]. Au[(TrCys)2B] was stable up to 4 h and formed smaller agglomerates over time compared to Au[(Met)2B]. The stabilisation of Au[(TrCys)2B] was achieved with 97 PBH units

compared to 57 units for Au[(Met)2B]. It appears that the TrCys group also selleck chemical conferred stability upon Au[(TrCys)2B]. Overall, these findings suggest that the TrCys residue and the steric bulk of PBH (Gly-Tyr-TrCys)2B are responsible for the remarkable stability of Au[(Gly-Tyr-TrCys)2B] agglomerates. The observations reported here have a major implication for the use of specific PBH capping agents in nanomaterial science. By applying PBH capping agents with different structures, the physico-chemical properties of AuNPs can be manipulated, thus affording tunability in Casein kinase 1 diverse environments. Interestingly, we observed

that the two PBH-capped AuNPs that showed increased stability, namely Au[(Gly-Tyr-TrCys)2B] and Au[(TrCys)2B], also produced the highest increase in ROS levels. However, significant ROS production was detected only at the two highest doses (50 and 100 μg/ml), thus indicating the feasibility of use at lower concentrations. Oxidative stress induction has been proposed as the principal mechanism of toxicity for many forms of NPs [57–59], including AuNPs [60]. Although the exact biological mechanism behind the action of the AuNPs was not determined in this study, we reveal that they all have the capacity to produce increased levels of ROS. However, the extent of this production differed depending on the PBH structures attached to the AuNP and the medium environment. ROS levels twofold higher than control levels were recorded after exposure to 100 μg/ml Au[(Gly-Tyr-TrCys)2B].