Effects of Cu^sup 2+^ on aggregation behavior of poly (l-Glutamic Acid)-functionalized gold nanoparticles

The effect of Cu^sup 2+^ ions on aggregation behaviors of poly (l-glutamic acid) (PLGA)-functionalized Au nanoparticles was investigated. It was found that the concentration of Cu^sup 2+^ ions had a significant influence on the folding and the formation of intermolecular hydrogen bonding of PLGA and thus the aggregation of the Au nanoparticles. In the absence of Cu^sup 2+^ ions, the Au nanoparticles underwent reversible pH-dependent aggregation attributed to the folding/unfolding of PLGA and the formation/breakage of intermolecular hydrogen bonds between PLGA molecules. In the presence of low concentration of Cu^sup 2+^ ions (i.e., 10 μM), folding of PLGA and aggregation of the Au nanoparticles were facilitated due to the charge screening effect of Cu^sup 2+^ ions, while the reversibility was partly maintained. In the presence of high concentration of Cu^sup 2+^ ions (i.e., 50 μM), aggregation of the Au nanoparticles was dominated by the coordination interaction between PLGA and Cu^sup 2+^ ions and the aggregation became irreversible due to the blocking of the formation of intermolecular hydrogen bonds by Cu^sup 2+^. These results suggested that Au nanoparticles may be used as a colorimetric probe to monitor the interactions between metal ions and peptides, which are essential for exploring the physiological effect of metals ions.[PUBLICATION ABSTRACT]