HEPES facilitates the formation and stability of gold nanostars

     Metal nanostructures, such as gold nanostars, nanotriangles, nanobipyramids, nanotubes exhibit large electric fields at their positive and negative curvature sites compared to neutral curvature features and structures. A common approach for synthesizing gold nanostars is a seedless and surfactant-free procedure using Good's buffers (HEPES, EPPS and MOPS). These reagents can be used as metal reducing agents, shape directing agents and stabilizers. Nanostars of different sizes and structures can be obtained by adjusting the buffer concentration and the pH of the solution.

Although HEPES is beneficial to the formation and structural stability of gold nanostars, little is known about the interaction of HEPES with metals. Recently, Xi et al. studied the acidification-induced restructuring of gold nanostars morphology and found that its morphology is dependent on the pH and acid composition, and is also affected by the protonation state of HEPES. They measured changes in molecular proton states using zeta potential and DFT methods. Surface-enhanced Raman scattering (SERS) reveals that pH changes induce reversible activation of the amine and sulfonate groups of HEPES, and redistribution of electrons weakens the affinity of HEPES to the metal, thereby facilitating adsorption.

The experimental results show that the restructuring of gold nanostars depends on protons in solution, which is consistent with the behavior of nanospheres with a diameter of about 6 nm dissolution under acid induction. In addition, the magnitude and restructuring rate of gold nanostars are related to the affinity of anions and gold. Through the study of the interaction between gold nanostars and HEPES, it was found that HEPES was partially displaced by benzene, and HEPES was reoriented when benzene adsorption or chemical enhancement associated with sulfonate groups of HEPES was weakened. Researchers speculate that partial desorption and changes in electron distribution in HEPES lead to reorientation.

In summary, HEPES affects the stability of gold nanostars and SERS detection of benzene. This effect is mainly due to the pH-dependent electronic distribution of HEPES, resulting in its affinity for the gold surface.

Related links: HEPES

References:

W. Xi, A. J. Haes, J. Am. Chem. Soc. DOI: 10.1021/jacs.8b13211

Edited by Suzhou Yacoo Science Co., Ltd.