Self-assembled Monolayer Of 4-mercaptobenzoic Acid Research Articles

Synthesis of silver nanoparticles with polyols under reflux and microwave irradiation conditions

Four polyols were used as stabilisers to synthesise silver nanospheres under reflux and microwave irradiation conditions. The nanoparticles were covered with a protective up to 10 nm silicon dioxide shell. The shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique was used to analyse the self-assembled monolayer of 4-mercaptobenzoic acid (4-MBA) by applying the produced silver core-silica shell nanoparticles. The article provides a detailed description of the synthesis, analysis and application of the nanoparticles based on UV/Vis, HR-TEM and SHINERS data.

Voltage-induced chemical contrast in scanning tunneling microscopy using tips chemically modified with hydrogen bond donors

In-situ voltage treatment to induce chemical contrast in scanning tunneling microscopy images has previously been demonstrated only in one case, i.e., with tips modified with a hydrogen bond acceptor. In this work, this method has been applied to induce chemical contrast using tips modified with a self-assembled monolayer of 4-mercaptobenzoic acid, a hydrogen bond donor. Chemical contrast enhancement, which allows recognition of particular functional groups, is ascribed to the chemically selective interaction of the hydrogen bond donating carboxyl group of 4-mercaptobenzoic acid and the hydrogen bond accepting ether oxygens in sample monolayers formed on highly oriented pyrolytic graphite. Surfaces initially showing no chemical contrast enhancement were made to show such contrast enhancement by applying a + 2.0 V pulse to the STM tip for 15 s. The chemical contrast could also be removed from images using 15 s treatments with a voltage of the opposite sign, i.e., − 2.0 V. The effectiveness of inducing chemical contrast using this voltage treatment and the tip lifetime are compared for tips modified with 4-mercaptopyridine and 4-mercaptobenzoic acid.

Chemisorption sensing and analysis using silicon cantilever sensor based on n-type metal–oxide–semiconductor transistor

This paper presents a silicon cantilever sensor based on n-type metal–oxide–semiconductor transistor for chemical sensing and analysis using the chemisorption-induced surface stress sensing principle. The cantilever is along the 〈1 0 0〉 crystal orientation of the (1 0 0) silicon, and the transistor channel is parallel to as well as located at the rear part of the cantilever to obtain high stress sensitivity. The gold film deposited on the bottom surfaces of cantilevers is chemically functionalized with a self-assembled monolayer of 4-mercaptobenzoic acid via the Au–SH covalent bonding. The vapor phase chemical sensing experiments with acetone, ethanol, nitroethane and water vapor as targets are performed. The observed response differentiation implies that the molecular interaction mechanisms between different chemical molecules are different.

Single gold nanostars enhance Raman scattering

Raman scattering from single gold nanostars coated with self-assembled monolayers of 4-mercaptobenzoic acid is observed. The Raman signal can be detected without the need of forming particle aggregates or resonant electronic excitation of the analyte. A total Raman enhancement factor of 107 for individual nanostars is estimated. These features make gold nanostars promising for Raman imaging in cells or cellular membranes.

Electrochemical and infrared spectroscopy studies of 4-mercaptobenzoic acid SAMs on gold surfaces

Cyclic voltammetry and Fourier transform infrared external reflection spectroscopy (FTIR-ERS) have been used to study self-assembled monolayers of 4-mercaptobenzoic acid (4-MBA) formed on gold surfaces. Electrochemical studies demonstrate that the carboxylic acid head group of 4-MBA can be protonated or deprotonated by application of an electric potential to the gold substrate. This effect is highly dependent on the pH of the electrolyte in accordance with models previously developed for acid-terminated monolayers. The voltammetric response decreases with prolonged exposure to moderate strength electrolytes as cations exchange with the acid terminus. The formation of either sodium or potassium carboxylate salts occurs relatively slowly but the presence of Ca 2+ ions in the electrolyte immediately quenches the electric-field driven protonation/deprotonation process. The latter process leads to a very stable carboxylate salt film, which cannot be reprotonated by prolonged exposure to the pure incubating solvent. FTIR-ERS studies demonstrate that the observed electrochemical response of the 4-MBA SAMs is related to the degree of hydrogen bonding in the monolayer film. The addition of ultrapure acetic acid to the incubating solution leads to a film with reduced levels of intermolecular hydrogen bonding between MBA molecules. Electrochemically, the voltammetric peaks associated with the protonation/depronation process are greatly attenuated when the self-assembled films are formed from solutions containing 4-MBA and acetic acid.

Sensitive detection of plastic explosives with self-assembled monolayer-coated microcantilevers

We report the detection of 10–30 parts-per-trillion levels of pentaerythritol tetranitrate and hexahydro-1,3,5-triazine within 20 s of exposure to a silicon microcantilever with its gold surface modified with a self-assembled monolayer of 4-mercaptobenzoic acid. These measurements correspond to a limit of detection of a few fg.

Carbon nanotube scanning tunneling microscopy tips for chemically selective imaging.

Carboxyl-terminated single-walled carbon nanotubes (SWNTs) were successfully immobilized from solution phases onto the apexes of gold tips for scanning tunneling microscopy (STM). Gold STM tips were first modified with self-assembled monolayers of 4-mercaptobenzoic acid, and its carboxyl groups were used to anchor carboxylated SWNTs through Zn2+ ion-bridged coordination. These SWNT tips gave high-resolution STM images of a diether monolayer formed on the graphite surface. In addition and more importantly, the ether oxygens of the sample molecules were selectively observed as bright spots with the SWNT tips with significantly high reproducibility, which is due to the facilitation of electron tunneling through hydrogen bond interactions between the ether oxygens and carboxyl groups at the end of the SWNT tips.

Controlled immobilization of peptide nanotube-templated metallic wires on Au surfaces

Peptide nanotubes were immobilized on Au substrates functionalized with self-assembled monolayers of 4-mercaptobenzoic acid in a pH 6 citric acid solution via hydrogen bonds between the peptide nanotubes and the monolayers. Subsequently, the immobilized nanotubes were metallized by nickel via the electroless coating process.

Conformational Rigidity in a Self-Assembled Monolayer of 4-Mercaptobenzoic Acid on Gold

Self-assembled monolayers of 4-mercaptobenzoic acid exhibit infrared spectral features for the carboxylic acid functionality that are characteristic of isolated vapor-phase molecules (e.g., sharp O-H stretch band, high-frequency non-hydrogen-bonded carbonyl stretch band) and inconsistent with molecules that are dimerized or that reside in condensed-phase hydrogen-bonding environments. This is in sharp contrast with the behavior of ω-mercaptoalkanoic acid monolayers, which exhibit spectral features characteristic of hydrogen-bonded and/or dimerized acid groups (e.g., no obvious O-H stretch band, lower frequency carbonyl stretch band). It is postulated that these characteristic differences reflect differing degrees of conformational rigidity in the monolayers, with the aromatic monolayers being sufficiently rigid and oriented as to prevent the intermolecular hydrogen bonding/dimerization that is commonly observed in aliphatic monolayers.