Bee Lean Ooi

Self-Assembly of Biomolecules on Electrode Surfaces; Oligonucleotides, Amino Acids, and Proteins toward the Single-Molecule Level

Publisher Summary This chapter presents an overview of some recent experimental and theoretical studies in a “bottom-up” fashion. The approach is from building blocks to higher organized systems that is, from mononucleotides to DNA fragments and from amino acids to proteins organized on single crystal surfaces. It provides a brief overview of molecular tunneling mechanisms in scanning tunneling microscopy (STM) and in situ STM and describes the features of the central substrate electrode systems mostly used, the single-crystal Au (1 1 1) surface. It overviews data for mono- and oligonucleotide monolayers and offers some views on electronic conduction mechanisms across adlayers of DNA-based molecules. It describes the electrochemical and in situ STM studies of amino acids and redox metalloproteins. The studies of artificial proteins on Au (1 1 1) have been presented. The approaches discussed offer ways of circumventing the “noise” problems by mapping precisely conditions where structural “coherence” can be expected to apply, with concomitant minimization of fluctuational effects on chemical and electronic function.

Assembled monolayers of Mo3S44+ clusters on well-defined surfaces

A class of inorganic monolayers formed by assembling the molybdenum-sulfur cluster, Mo3S4(4+), onto a well-defined Au(111) surface is presented. The monolayers have been comprehensively characterized by electrochemistry, X-ray photoelectron spectroscopy (XPS), and in situ scanning tunneling microscopy (in situ STM). The voltammetric data show strong reductive and oxidative desorption signals from Au-S interactions, supported by the presence of both S and Mo signals in XPS. In situ STM shows many small pits in the dense adlayers uniformly spread over the surface, which is a typical feature of self-assembled monolayers (SAMs) of alkanethiols. The density of the pits is ca. 23 (+/-5)% and is significantly higher than for straight-chain alkanethiol SAMs with a single -SH group. The pit shapes are irregular, suggesting multiple Au-S interactions from Mo3S4(4+). High resolution images disclose bright round spots of ca. 8 A diameter representing individual molecules in the SAM. This is the first example of in situ monolayer formation by a metal-chalcogenide cluster directly anchored onto the gold surface through core ligands and offers a simple way to prepare a new class of functionalized inorganic monolayers.