The absorbance spectrum of A) citrate-stabilized AuNP before and after addition 0.4 M NaCl and 1x PBS, B) AuMN-DTTC before and after addition of 0.4 M NaCl and 1x PBS, and C) AuMN-DTTC incubation in fetal bovine serum. Change in absorbance over time of D) AuNP after the addition of 0.4 M NaCl and 1x PBS (arrow shows the point of addition), E) AuMN-DTTC after the addition of 0.4 M NaCl and 1x PBS, F) AuMN-DTTC in fetal bovine serum. Unlike AuNP, the AuMN-DTTC nanoparticles remained stable long-term both in high-salt conditions and in serum.