The studies of poly (amino acid) assisted synthesis of gold nanoparticles

In the past decade, bio-inspired chemistry using organized biomolecules, such as peptides, proteins, viruses, and enzymes, has demonstrated the power for assembling and structure-directing small species into unique materials due to their highly elaborate, self-assembling capability in nature, leading to the emergence of unique physiological properties. In this work, we used Poly-L-Lysine (PLL) or Poly-L-Glutamic acid (PLGA) to assist the synthesis of gold nanoparticles. Both PLL and PLGA are poly-peptides with non-toxic, and harmless for the environment and human. Therefore, our nanoparticle synthesis process is consistent with the recent trend of green chemistry. The PLL or PLGA solutions ware prepared respectively by dissolving PLL or PLGA in D.I. water. After adding a freshly prepared HAuCl₄ solution to the poly-peptide solutions and stirring, the solution color slowly changed with time. The variation of solution color was attributed to the surface plasmon resonance (SPR) of gold nanoparticles, which was demonstrated by the SEM investigation. The experimental results showed that both the PLL and PLGA successfully assisted the synthesis of gold nanoparticles. The particle size increased with the reaction time but with the reduction of pH value. The influences of reaction time and solution pH value on the precipitated Au nanoparticles were discussed. By employing an appropriate solution conditions (e.g. reduction time and solution pH value), we can obtain the Au nanoparticle with an adequate size for application.