Mechanism and Cellular Kinetic Studies of the Enhancement of Antioxidant Activity by Using Surface-Functionalized Gold Nanoparticles

The enhanced antioxidant ac- tivity of surface-functionalized gold nanoparticles (AuNPs) synthesized by self-assembly has attracted great atten- tion, but little is known about the mechanism behind the enhanced activi- ty. To address this challenge, the anti- oxidant activity of Au@PEG3SA (i.e., surface-functionalization of spherical AuNPs with the antioxidant salvianic acid A) was used as an example to il- lustrate the mechanism of the en- hanced activity. Evaluation of the anti- oxidant activity was performed in a radical-scavenging reaction between Au@PEG3SA and 2,2-diphenyl-1-pic- rylhydrazyl (DPPH) radical. As expect- ed, the rate constant for the reaction of Au@PEG3SA with DPPH was about nine times greater than that for the sal- vianic acid A monomer. A comparative analysis of the spectral characteristics of Au@PEG3SA and the salvianic acid A monomer further imply that the enhancement of the antioxidative re- A kinetics may be ascribed to the variation in the transition state for the DPPH-radical scavenging reaction through p-p stacking interactions be- tween and among adjacent groups on the surface of Au@PEG3SA. On the other hand, the kinetic enhancement of Au@PEG3SA on reactive-oxygen-spe- cies (ROS) scavenging can be observed in living cells and in vivo, which possi- bly provides new insight for the bioap- plication of self-assembly of surface- functionalized AuNPs.