Seong-Hun Song

Analysis of Im-SH self-assembled monolayer formation and its interaction with Fe2+ and Zn2+ using quartz chemical analyzer

Abstract A self-assembly process and dynamic property changes of N -[2-(4-imidazolyl)ethyl]11-mercaptoundecanamide (Im-SH) on gold electrode have been investigated measuring the resonant and electrochemical parameters of quartz crystal using a quartz chemical analyzer and an impedance analyzer. The morphological changes on gold surface have also been investigated using an optical microscopy and a STM. The affinity differences of assembled film for Zn 2+ and Fe 2+ have also been investigated by the electrochemical experiments. As a result, a two-step process is found in the self-assembly by utilizing abundant analytical variables from the impedance analyzer and a molecular level conformational change has been detected in the scanning tunneling microscopy (STM) images for the self-assembled monolayer (SAM) film and the metal ions bonded film. The conformational change is well corresponding to the electrochemical results.

THE ELECTROCHEMICAL STUDIES ON A SELF-ASSEMBLED VIOLOGEN MONOLAYER USING QUARTZ CRYSTAL MICROBALANCE

The electrochemical behavior of viologen self-assembly monolayer has been investigated with QCM, which has been known as nano-gram order mass detector. The self-assembly process of viologen was monitored using resonant frequency (ΔF) and resonant resistance (R). The QCM measurements indicated a mass adsorption for viologen assembling on the gold surface with a frequency change about 135 Hz and calculated its surface coverage (Γ) to be 3.5273×10−9 mol/cm2. Also a reversible redox process was observed and analyzed with an ionic interaction at the viologen/solution interface using ▵F.

Analysis of the structure and morphology of oligopeptide SAM using XPS and AFM

Oligopeptides such as PSP1 (Tyr-Ala-Gly-Tyr-Cys) and PSP2 (His-Ala-Ser-Tyr-Ser-Cys), which interact strongly with a typical cationic porphyrin derivative, are synthesized. The structure and morphology of PSP1 and PSP2 monolayers self-assembled on Au surface have been investigated by using X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). XPS of the monolayers provides evidence that the primary adsorbate species are bonded to Au through the sulfur atom comprised in the species. It is revealed from XPS spectroscopy and AFM images that PSP2 is self-assembled better on Au surface than PSP1. This experimental result is well consistent with the prediction based on steric energies of Au-Peptide bond.

QCM analysis for the formation of a self-assembled peptide membrane and high sensitivity detection of porphyrin

In this study, the purpose was to construct a system for the high sensitivity detection of low molecular weight compounds using a peptide ligand and quartz crystal analyzer (QCA). Porphyrin (H/sub 2/TMpyP) was used as the target compound and a self-assembled monolayer (SAM) of porphyrin binding peptide was used as a ligand. The peptide SAM formation on the gold surface was monitored by the measurement of the resonant frequency. The interaction between the peptide SAM and porphyrin was continuously detected using QCA. The clear frequency decrease for the peptide-SAM formation and porphyrin binding appeared readily after the injection of peptide solution and porphyrin solution. Although in the direct measurements the frequency decrease was observed only for high-concentrated porphyrin over 20 /spl mu/g/ml. The detection system could be improved by the addition of peptides immobilized on latex beads used as a mass-sensitizer. The detection limit of this system was 10 ng/ml.

An In Situ Analysis of a Self-Assembly Process of an α-Imidazolyl-ω-Alkanethiol on Gold by a Quartz Crystal Analyzer

Abstract A self-assembly process of N-[2-(4-imidazolyl)ethyl]11-mercaptoundecan-amide (Im-SH) on gold surface was monitored by in situ measurements of the resonant frequency and the resonant resistance of a quartz crystal analyzer (QCA) together with optical and atomic force microscopy. The Q factor was applied to evaluate the homogeneity of the adsorbed monolayer. A two-step process was involved in the monolayer formation. At the first stage, a fast adsorption to the surface up to 90% was produced, and then the dot-like Im-SH monolayers became to reorganize and reassemble to form a much larger aggregated monolayer.