Monolayer Of 3-mercaptopropionic Acid Research Articles

Rapid detection of Salmonella enteritidis by piezoelectric immunosensor

Comparative testing of three different coatings for the immobilization of the anti- Salmonella enteritidis antibody onto piezoelectric (PZ) crystals with gold, silver and palladium electrodes was done. In terms of stability, simplicity and magnitude of the frequency change caused by antibody binding to the coating, polyethyleneimine film gave the better results for the immobilization of antibody as compared with the (γ-aminopropyl)trimethoxysilane film or the self-assembled monolayer of 3-mercaptopropionic acid. To reduce the production cost, the small-sized crystal with silver electrodes was used to fabricate the disposable antibody-modified PZ transducer. The rapid detection of Salmonella enteritidis was successfully performed using the antibody-modified PZ immunosensor. A detection limit of 1×10 5 cells/ml and an assay time of 35 min were achieved.

In situ STM study of self-assembled mercaptopropionic acid monolayers for electrochemical detection of dopamine

An Au(111) electrode coated with a self-assembled monolayer of 3-mercaptopropionic acid (MPA) has been investigated by square-wave voltammetry for electrochemical detection of dopamine in the presence of ascorbic acid and characterized by in situ STM. The electrode is found to shift selectively the unwanted oxidation of ascorbic acid to higher potentials while leaving the oxidation of dopamine unchanged. The selectivity is lost below ∼−0.5 V (Ag ∣ AgCl ∣ 3 M KCl) due to a reductive desorption of MPA, and also above ∼1.2 V where the Au electrode begins to oxidize. STM shows that even a brief oxidation results in large change in the molecular packing structure of the MPA monolayer. Before the oxidation, the MPA molecules in the monolayer pack into several phases. The most dominant phase is an incommensurate p×√3 structure, while commensurate phases, 5×√3, 6×√3, 8×√3 and 10×√3 have also been observed frequently. In some areas, the molecules pack into a superlattice 3×4√3 that can be attributed to a periodic mixing of two discrete conformations of MPA. After cycling the potential to the oxidation potentials, the ordered structures transform into a less compact disordered structure. The exposed bare Au electrode in the disordered structure is believed to be responsible for the loss of the electrode selectivity.

Rapid measurement of transaminase activities using an amperometric l-glutamate-sensing electrode based on a glutamate oxidase–polyion complex-bilayer membrane

An amperometric l-glutamate-sensing electrode was prepared by immobilizing glutamate oxidase (GlOx) on a polyion complex layer-modified electrode. First, a monolayer of 3-mercaptopropionic acid was made on the surface of a gold electrode by immersing it in an ethanol solution containing the modifier. Next, aqueous solutions of poly-l-lysine and poly(4-styrenesulfonate) were successively placed on the electrode surface and allowed to dry. Finally, a GlOx layer was formed on the poly-l-lysine/poly(4-styrenesulfonate)-complex layer by crosslinking the enzyme by the addition of a glutaraldehyde solution. The use of thin bilayer system with the inner, polyion complex membrane, which showed permselectivity based on the solute size with the molecular cut-off of ≈100, brought high performance characteristics to the l-glutamate-sensing electrode; it showed high sensitivity (detection limit, 20 nM), rapid response (100% response time, 3 s), low interferential level (the ratio of response for l-ascorbic acid to that for the same concentration of l-glutamic acid, 8×10−2), and high stability (usable for more than a month). The bilayer-based electrode was useful for the rapid measurement of glutamate–oxaloacetate transaminase (GOT) and glutamate–pyruvate transaminase (GPT) in serum sample: each transaminase (0.2–1000 U l−1) could be determined within 10 s.

Determination of Real Composition of 3-Mercaptopropionic Acid and 1-Octadecanethiol Mixed Self-Assembled Monolayers by Using Electrochemical and Electrochemical Quartz Crystal Microbalance Measurements

In order to clarify the electrochemical response of cytochrome c at the gold electrode modified with mixed monolayers of carboxylic acid terminated alkanethiol (promoter molecule) and n-alkanethiol (barrier molecule), electrochemical and electrochemical quartz crystal microbalance (EQCM) measurements were carried out during the reductive desorption of the mixed monolayer of 3-mercaptopropionic acid and 1-octadecanethiol (C18SH) in alkaline solution. The ratio of mercaptopropionic acid in the mixed monolayer was found to be smaller than that in the modifying solution, showing that C18SH adsorbed more preferentially than mercaptopropionic acid. The peak potentials for the reductive desorption of mercaptopropionic acid became more negative upon increasing the C18SH content in the monolayer. This means mercaptopropionic acid and C18SH did not form patched domains but were mixed well with each other. The mercaptopropionic acid molecules in a well-mixed monolayer should be stabilized through the affinity between the mercaptopropionic acid and C18SH and becomes difficult to be desorbed from the electrode.

Glucose oxidase/polyion complex-bilayer membrane for elimination of electroactive interferents in amperometric glucose sensor

An amperometric glucose-sensing electrode was prepared by immobilizing glucose oxidase (GOx) on a polyion complex membrane. First, a monolayer of 3-mercaptopropionic acid (MPA) was made on the surface of a gold electrode by immersing it in an ethanol solution containing MPA. Aqueous solutions of poly- l-lysine and poly-4-styrenesulfonate were successively placed on the electrode surface and allowed to dry. A GOx layer was then formed on the poly- l-lysine/poly-4-styrenesulfonate-complex layer by crosslinking the enzyme by the addition of a glutaraldehyde solution. The polyion complex layer was effective for eliminating electrochemical interferents such as l-ascorbic acid, uric acid and acetaminophen, whereas the hydrogen peroxide produced through the GOx-catalyzed reaction permeated rapidly through the layer. This resulted in a rapid response (100% response in <5 s) with a low interference level (e.g., the ratio of response for l-ascorbic acid to that for the same concentration of glucose was 0.07). The electrode was applied to the assay of glucose in beverages and sera, and could be used for more than two months.

Electrochemical responses of cytochrome c on a gold electrode modified with mixed monolayers of 3-mercaptopropionic acid and n-alkanethiol

The electrochemical behavior of cytochrome c on gold electrodes modified in solution containing a mixture of 3-mercaptopropionic acid and n-alkanethiol having various chain lengths was investigated and compared with that of another mixed monolayer system, bis(4-pyridyl) disulfide and n-alkanethiol, previously reported. The peak current decreased with the increase of the ratio of n-alkanethiol in the 3-mercaptopropionic acid + n-alkanethiol mixture, as was observed in the case of bis(4-pyridyl) disulfide + n-alkanethiol mixture. The n-alkanethiol with a longer chain was more effective in blocking the electron exchange between cytochrome c and the electrode than that with a shorter chain, in contrast to the results observed at the mixed monolayer of bis(4-pyridyl) disulfide and n-alkanethiol. This observation reflects the fact that adsorbed molecules were well mixed with each other in the case of the 3-mercaptopropionic acid + n-alkanethiol mixed monolayers, while patched domains of pyridyl thiolate were formed in the case of the mixed monolayers of bis(4-pyridyl) disulfide and n-octadecyl mercaptan. The electrochemical behavior of the gold electrodes modified with the mixed monolayer of 3-mercaptopropionic acid and n-alkanethiol in the solution containing Fe(CN)64−3− supports the above observation. Reductive desorption of the mixed monolayer was carried out in alkaline solution to determine the composition and to evaluate the degree of mixing of the two components.

Impedance analysis of ion transport through gramicidin channels incorporated in solid supported lipid bilayers

The topic of this study is a solid supported lipid bilayer consisting of dimethyldioctadecylammoniumbromide (DODAB) and the channel-forming polypeptide, gramicidin D, from Bacillus brevis immobilized on gold electrodes. The peptide was reconstituted into large unilamellar vesicles of DODAN which were fused on a negatively charged monolayer of 3-mercaptopropionic acid. The peptide forms a pore of 4 Å diameter, selective, selective for monovalent cations. The sequence of conductivity of monovalent alkaline cations is Cs +>K +>Na +>Li +. The transport of these monovalent cations through this supported lipid bilayer via the gramicidin dimer was observed by a.c. impedance spectroscopy as an integral electrochemical method. Only a single bilayer preparation was necessary to perform the whole measurement. The obtained data were analysed with an equivalent circuit based on the theory developed by de Levie. We succeeded in confirming the sequence of the conductivity by impedance spectroscopy. The conductance of the membrane shows a linear dependence on the concentration of the cations in the bulk phase. This system is therefore recommended for biosensor devices based on ion transport through solid supported membranes.

Direct electron transfer to cytochrome c oxidase in self-assembled monolayers on gold electrodes

The monolayer of cytochrome c oxidase maintaining physiological activity and attached covalently to the self-assembled monolayers of 3-mercaptopropionic acid (MPA) on a gold electrode was obtained. The results of cyclic voltammetry show that direct electron transfer between cytochrome c oxidase and the electrode surface is a fast and diffusionless process. MPA has a dual role as both electrode modifier and the bridging molecule which keeps cytochrome c oxidase at an appropriate orientation without denaturation and enables direct electron transfer between the protein and the modified electrode. Immobilized cytochrome c oxidase exhibits biphasic phenomena between the concentration of the electrolyte and the normal potentials; meanwhile its electrochemical behavior is also influenced by the buffer components. The quasi-reversible electron transfer process of cytochrome c oxidase with formal potential 385 mV vs. SHE in 5 mM phosphate buffer solution (pH 6.4) corresponds to the redox reaction of cyt a 3 in cytochrome c oxidase, and the heterogeneous electron transfer rate constant obtained is 1.56 s −1. By cyclic voltammetry measurements, it was observed that oxidation and reduction of cytochrome c in solution were catalyzed by the immobilized cytochrome c oxidase. This cytochrome c oxidase¦MPA¦Au system provides a good mimetic model to study the physiological functions of membrane-associated enzymes and hopefully to build a third-generation biosensor without using a mediator.

Applications of impedance spectroscopy in biochemistry and biophysics.

The present study is intended to demonstrate the application of impedance spectroscopy to two very different fields of biophysical research. The core component of our measuring setup is a self-constructed continuous wave impedance spectrometer together with special measuring chambers which are individually designed for the systems under investigation. We directed our attention towards: i) the investigation of solid supported lipid bilayers in general, especially systems which are suitable for protein reconstitution such as dimethyldioctadecylammonium bromide (DODAB) immobilized onto a gold electrode, precovered with a negatively charged monolayer of 3-mercaptopropionic acid. Impedance spectroscopy allows to study the stability, the thickness and the electrode coverage of those artificial membranes as well as the observation of ion transport mediated by ionophores like gramicidin D incorporated into a DODAB-bilayer. ii) The characterization of the passive electrical properties of epithelial and endothelial cell monolayers in general and especially the determination of their transepithelial (transendothelial) electrical resistances as a measure for epithelial barrier function. From impedance spectra, as reported here, we are able to follow the formation and modulation of cell layer permeability to small ions.

Plasma protein and antisera interactions with L-cysteine and 3-mercaptopropionic acid monolayers on gold surfaces

Plasma Protein and Antisera Interactions with L-Cysteine and 3-Mercaptopropionic Acid Monolayers on Gold Surfaces