By comparing the micrographs, the highest degree of agglomeration in the case of Au[(Gly-Tyr-Met)2B] (Figure 7e,f) after suspension in medium can be appreciated. Therefore, one would expect the surface chemistry of these NPs upon interaction with media not to be the same as for the NPs initially prepared [53]. Figure 7 TEM images of AuNPs in EMEM/S- after preparation. (a) Au[(TrCys)2B], (c) Au[(Gly-Tyr-TrCys)2B] and (e) Au[(Gly-Tyr-Met)2B], Epacadostat cell line and at 24 h of incubation; (b) Au[(TrCys)2B], (d) Au[(Gly-Tyr-TrCys)2B] and (f) Au[(Gly-Tyr-Met)2B]

[Scale bar (c) and (d) is 20 nm, and for all other images, scale bar is 50 nm]; asterisk and bold letters are used to GDC-0994 nmr signal the most stable AuNP. Optical microscopy and visual sedimentation of AuNP suspensions Large distinctive agglomerates of micrometre scale were observed for all AuNP preparations when viewed under an optical microscope (Figure 8), with the exception of Au[(Gly-Tyr-TrCys)2B] (Figure 8b). Also upon visual observation of the AuNP suspensions in the different medium suspensions after 24 h of incubation, we made some key observations regarding sedimentation over time. After 24 h of incubation in EMEM/S-, Au[(Gly-Trp-Met)2B], Au[(Gly-Tyr-Met)2B], Au[(Met)2B] and Au[(TrCys)2B] sedimented out of solution, as determined by the presence of a pellet at the bottom of the tubes. Au[(Gly-Tyr-TrCys)2B]

remained dispersed in solution, having a visibly darker appearance in suspension. In the case of the serum-containing medium, MycoClean Mycoplasma Removal Kit EMEM/S+, sedimentation

was less apparent. AuNP Au[(Gly-Tyr-TrCys)2B], along with Au[(Met)2B] and Au[(TrCys)2B], had a visibly darker appearance, thereby suggesting different dispersion rates for these particles when serum was present. Figure 8 PBH-capped AuNPs (100 μg/ml) after 24-h incubation in EMEM/S- as viewed using optical microscope. (a) Au[(Gly-Trp-Met)2B], (b) Au[(Gly-Tyr-TrCys)2B], (c) Au[(Gly-Tyr-Met)2B, (d) Au[(Met)2B and (e) Au[(TrCys)2B]; asterisk and bold letters are used to signal the most stable AuNP. Toxicity studies Interference of AuNPs with toxicity assays AuNP concentration-dependent interference was detected with the toxicity assays used in this study (Figure 9). In the case of the commonly used MTT and NRU assays, absorbance is used as the assay readout. Concentration-dependent interference by control samples containing AuNPs without cells was observed at both of the wavelengths used, 570 and 550 nm, as a result of the absorbance of AuNPs at the same wavelengths (Figure 9a,b). A concentration-dependent increase in absorbance levels was evident from a 6.25 μg/ml exposure concentration, which reached a 500% increase at the highest concentration used in this study (100 μg/ml) for both wavelengths.