Quantifying the Selective Modification of Au(111) Facets via Electrochemical and Electroless Treatments for Manipulating Gold Nanorod Surface Composition

Abstract

Manipulating the composition of a mixed alkylthiol self-assembled monolayer (SAM) modified gold surface using both electrochemical and electroless methods is demonstrated. Through the use of fluorophore labeled thiolated DNA and in situ fluorescence microscopy with a gold single crystal bead electrode, a procedure was developed to study and quantify the selective desorption of an alkylthiolate SAM. This method enabled a self-consistent measurement of the removal of the SAM from the 111 surface compared to the 100 surface region at various potentials. A 20-fold increase in the electrochemical removal and replacement of the SAM from the 111 surface over the 100 surface was realized at -0.8 V/AgAgCl. A related procedure was developed for the solution-based electroless removal of the SAM using NaBH achieving a similar selectivity at the same potential. Unfortunately, in the electroless process fine control over the reducing potential was difficult to achieve. In addition, working in the presence of O complicates the solution potential measurement due to depolarization by the reduction of O, resulting in a less clear relationship between selectivity and measured solution potential. Interestingly, the electrochemical method was not disturbed by the presence of O. In preparation for work with Au nanorods, electrochemical measurements were performed in electrolyte that included 1 mM CTAB and was found to not interfere with this method. Preliminary results are promising for using this methodology for treatment of acid-terminated alkylthiol modified Au nanorods.

Electrodepositing DNA Self-Assembled Monolayers on Au: Detailing the Influence of Electrical Potential Perturbation and Surface Crystallography

“…Increasing the positive potential limit significantly increased the DNA coverage in these regions, specifically along the 100–210–110 zone. This is also the case when analyzing the regions that surround the 111 facet, which are similar to small 111 terraces separated by many steps . In agreement with the previous study, an increase in the positive electrodeposition potentials results in greater MCH SAM instability and facilitated DNA thiol-exchange.…”

One-Dimensional Metal Nanostructures: From Colloidal Syntheses to Applications

“…This result supported the hypothesis that CTAB preferentially adsorbs onto Au{100} facets during the growth of AuNRs. 178 Single-crystal electrodes were also used to test the hypothesis of capping agent for the growth of penta-twinned CuNWs in a highly basic solution (15 M NaOH) containing EDA. 177 It has been hypothesized that EDA acted as a capping agent that preferentially adsorbed onto the side faces of NWs, the {100} facets, while less EDA adsorbed at the ends of the growing NWs terminated in the {111} facets, leading to the selective addition of Cu to the ends of the NWs.…”

“…Notable examples include in situ TEM, ,,,− dark-field optical microscopy (DFOM), ,− and transmission X-ray microscopy (TXM). − All these techniques have been used to observe the growth of 1D metal nanostructures in real time, quantify their growth kinetics, and distinguish between atomic addition and oriented attachment. In addition, single-crystal electrochemistry has provided new insights into the roles played by halides and capping agents during anisotropic growth. − Computational simulations have also been used to evaluate different hypotheses pertaining to how anisotropic growth occurs, offering additional insights into atomic-level processes that determine the rates of anisotropic growth, as well as why anisotropic growth occurs. − ,,− This section focuses on the contributions made by these new analytical methods, each of which can contribute a different perspective on the development and testing of models to account for 1D growth.…”

“…Measurements of the surface reactivity as a function of crystal orientation and the concentration of adsorbate can test this hypothesis and offer a deep understanding of the facet-dependent chemistry that causes anisotropic growth of 1D metal nanostructures. To this end, single-crystal electrochemical measurements have been demonstrated as a powerful analytical tool for obtaining such information in the fields of electrocatalysts, − electrochemical deposition, ,− and corrosion. − To date, single-crystal electrochemistry has been used to test the hypothesis of capping agent for AuNR and CuNW growth. − There remain many additional nanostructure syntheses in which single-crystal electrochemistry can be applied to provide a deeper understanding of the facet-selective chemistry.…”

“…This situation differs from the solution-phase synthesis, in which the two crystal facets are in electrical contact, and therefore will presumably be at the same potential. To address this issue, researchers used single-crystal Au bead electrodes consisting of four Au(111) surfaces and one Au(100) surface . These electrodes are made by flame annealing the end of a gold wire.…”