Cysteamine Self-assembled Monolayer Research Articles

An amperometric horseradish peroxidase inhibition biosensor based on a cysteamine self-assembled monolayer for the determination of sulfides

An amperometric horseradish peroxidase (HRP) inhibition biosensor based on a thiolate self-assembled monolayer (SAM) has been developed for the determination of sulfides (HS −, H 2S and small amount S 2−). Cysteamine SAM was applied to the gold electrode surface and HRP was then immobilized on the electrode by cross-linking with glutaraldehyde. The measurement was performed in the presence of an electron mediator hydroquinone and 0.067 M phosphate buffer of pH 6.5 at an applied potential of −150 mV versus SCE. The determination of sulfides can be achieved in the range of 0.5–12.7 μM with a detection limit of 0.3 μM. The kinetic parameters Michaelis–Menten constant ( K m app) and maximum current ( I max) with and without inhibitor have also been calculated and possible mechanism has been deduced according to the variation of K m app.

A novel immunosensor based on self-assembled chitosan/alginate multilayers for the detection of factor B

A piezoelectric immunosensor based on a novel immobilization strategy combining cysteamine self-assembled monolayer (SAM) and chitosan/alginate adsorption procedure has been developed for the determination of factor B in human serum. Cysteamine SAM was first applied to the gold electrode surface of the crystal, and a strong positively-charged chitosan monolayer was posed on the cysteamine SAM by using glutaraldehyde cross-linking. Alginate-factor B was then electrostatically immobilized on the crystal with the aid of the negatively-charged alginate layer. The conditions of immobilizing antibodies were optimized in detail. Comparing with the conventional glutaraldehyde covalent immobilization, the immunosensor with the proposed immobilization procedure shows an improved performance in terms of the magnitude of the response and sensitivity. Moreover, the proposed immobilization procedure results in immobilized entities with relatively high biological activity and favorable immunosensing characteristics. The PQC devices are readily regenerated. Analytical results obtained from the tests of non-specific adsorption and recoveries indicated that the immunosensor prepared by use of the chitosan/alginate adsorption procedure is a useful tool for the determination of factor B in plasma in clinical diagnosis.

Catalytic Monolayer Voltammetry and In Situ Scanning Tunneling Microscopy of Copper Nitrite Reductase on Cysteamine-Modified Au(111) Electrodes

We have studied the adsorption and electrocatalysis of the redox metalloenzyme blue copper nitrite reductase from Achromobacter xylosoxidans (AxCuNiR) on single-crystal Au(111)-electrode surfaces modified by a self-assembled monolayer of cysteamine. A combination of cyclic voltammetry and in situ electrochemical scanning tunneling microscopy (in situ STM) directly in aqueous acetate buffer, pH 6.0 has been used. High-resolution in situ STM shows that cysteamine packs into ordered domains with strip features of a periodic distance of 11.7 ± 0.3 A. No voltammetric signals of the nitrite substrate on this surface could be detected. A strong cathodic catalytic wave appears in the presence of nitrite. The catalytic current follows a Michaelis−Menten pattern with a Michaelis constant of Km ≈ 44 μM, which is close to the value for AxCuNiR in homogeneous solution. The apparent catalytic rate constant based on a dense monolayer is kcat = 6−10 s-1. This is significantly lower than two reported values of 185 s-1 and...

Solvent Effect on Formation of Cysteamine Self-Assembled Monolayers on Au(111)

Cysteamine (CA) self-assembled monolayers (SAMs) formed in various solutions on Au(111) were examined by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) to understand the solvent effect on the SAM structure. The STM study revealed that the surface structure of CA SAMs prepared in polar protic solutions was strongly influenced by immersion time, while there were no significant structural changes in the SAMs prepared in nonpolar and polar aprotic solutions. This result implies that the proticity of the solvent and the immersion time play important roles in determining the surface structures of the amino-terminated CA SAMs due to the coadsorptoin of solvent molecules onto the clean monolayers, which are stabilized by hydrogen bonding between polar protic solvents and the clean monolayers. In addition, our STM and XPS results for CA SAMs on Au(111) suggest the existence of two different structural conformations, i.e., trans and gauche conformers.

An STM Study on Solvent Effects in Forming Self-Assembled Cysteamine and Propanethiol Monolayers on Au(111)

The morphologies of cysteamine (CA) and propanethiol (PT) self-assembled monolayers (SAMs) on Au(111) prepared in H 2 O, ethanol, N,N,-dimenthylformamide (DMF), and toluene solution were imaged by scanning tunneling microscopy (STM). The STM measurements showed that the formation of domains like dendrites in CA SAMs was dependent on a type of solvent. On the other hand, a pit size in PT SAMs was controlled by a type of solvent without such a domain formation. These results clearly revealed that the solvent plays an important role in SAM formation.

An STM Study on Solvent Effects in Forming Self-Assembled Cysteamine and Propanethiol Monolayers on Au(111)

The morphologies of cysteamine (CA) and propanethiol (PT) self-assembled monolayers (SAMs) on Au(111) prepared in H 2 O, ethanol, N,N,-dimenthylformamide (DMF), and toluene solution were imaged by scanning tunneling microscopy (STM). The STM measurements showed that the formation of domains like dendrites in CA SAMs was dependent on a type of solvent. On the other hand, a pit size in PT SAMs was controlled by a type of solvent without such a domain formation. These results clearly revealed that the solvent plays an important role in SAM formation.

Formation and Characterization of Heteropolyacid/Polycation Multilayer Films on Gold Electrode

Ultrathin multilayer films of a polybasic lanthanide heteropoly tungstate-molybdate complex and a cationic polymer of quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2′-bipyridine) have been fabricated on a gold electrode precoated with a cysteamine self-assembled monolayer. The multilayer films have been characterized by optical spectroscopy, small-angle X-ray diffraction, and electrochemical methods (cyclic voltammetry and electrochemical impedance). Especially, the electrochemical impedance spectroscopy is developed to monitor the layer deposition processes. It provides important information such as double-layer capacitance and charge-transfer resistance. All obtained results reveal regular film growth with each layer adsorption. © 2001 The Electrochemical Society. All rights reserved.

Direct Voltammetric Observation of Reversible and Irreversible Oxidations of Two-Dimensional J-Aggregates of Cyanine Dye

The redox properties of two-dimensional (2D) J-aggregates of a typical thiacarbocyanine dye have been studied directly by the standard electrochemical method in conjunction with the recently developed technique for controlled layering of 2D J-aggregates on a self-assembled cysteamine monolayer on an atomically flat Au(111). The cyclic voltammograms measured at widely ranging scan rates from 10 mV/s to 100 V/s illuminated unique mechanistic features of the J-aggregate oxidation, which proved to be a convolution of reversible and irreversible oxidations involving the charge transfer of up to 4 electrons/molecule. The oxidation-induced irreversible bleaching of the J-band was accompanied by negligibly small changes in its peak position and sharpness, suggesting that the irreversible reaction occurs preferentially along the domain edges or boundaries. The two different phases of oxidation could be more or less clearly separated under the fast scan mode (scan rate larger than ∼10 V/s), giving us the unpreceden...

Controlled Layering of Two-Dimensional J-Aggregate of Anionic Cyanine Dye on Self-Assembled Cysteamine Monolayer on Au(111)

An anionic cyanine dye with disulfopropyl substituents allowed its two-dimensional (2D) J-aggregate of highest-ever quality to be successfully layered on top of the self-assembled monolayer (SAM) of cysteamine (CA) on atomically flat Au(111). The chemisorption of CA from millimolar ethanolic solutions was rapid, producing an estimated density of surface amino groups of ∼4 × 1014 cm-2 well within a minute. However, sufficient ordering of the CA SAM, which we found by scanning tunneling microscopy imaging to yield a characteristic 7 × √3 superlattice structure, took a considerably long extra immersion time of a few hours at room temperature. The highest-quality 2D J-aggregate with an extraordinary sharp J-band formed preferentially on densest but still not fully ordered CA SAMs, from typically 0.1 mM dye solutions in 1:1 mixed water and ethanol solvent at considerably high adsorption temperatures of 50−65 °C. A detailed analysis of the 2D J-aggregate and its molecular linkage with the CA SAM indicated that 1.3 × 1014 cm-2 dye molecules are individually anchored to the surface amino groups in the form of ammonium sulfonates. The resultant energy barrier for the 2D J-aggregation can still be overcome at the given high temperature of dye adsorption in the case of nonrigid (only partially ordered) CA SAMs because of the strong cohesive interactions between dye molecules possibly exceeding ∼50 kJ/mol. Other important questions such as the electric charge balance in the layered assembly and the overall chemistry of 2D J-aggregation are also addressed.

Fabrication of Two-Dimensional J-Aggregates on Au(111) Covered with Self-Assembled Cysteamine Monolayer

Abstract A simple and useful new method to fabricate high-quality 2D J-aggregates of anionic cyanine dyes on a solid surface has been established by using an Au(111) covered with cysteamine self-assembled monolayer. It was also found that this method allows easy control of dye aggregation ranging from a 2D crystalline J-aggregate to a high density of dye monomers without aggregation.

Screen-Printed Amperometric Immunosensor for Repeated Use in the Flow-Through Mode

The screen-printed electrochemical system was used for construction of the regenerable flow-through immunosensor for determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The gold-based composite electrode was modified with a self-assembled monolayer of cysteamine and the obtained aminogroup was linked to 2,4-D using the common N-hydroxysuccinimide/carbodiimide reaction. This immunosensor was employed in a flow-through system with the monoclonal antibody E2/G2 conjugated to peroxidase as a tracer. The peroxidase activity retained in immunocomplexes at the electrode surface was quantified amperometrically at –50 mV vs. the screen-printed silver pseudoreference electrode, hydrogen peroxide and iodide were used as substrates. Repeated use of the immunosensor was successfully achieved using regeneration with pepsin at pH 2 at the end of each assay cycle. The calibration plot for the competitive determination of 2,4-D was constructed from 0.01 to 100 μg/L; limit of detection (based on the 20 % decrease of relative binding of the tracer) was 0.12 μg/L. One analytical cycle lasted for 30 min; the same immunosensor can be used for 20 assays. Performance of similar electrochemical immunosensors based on the same antibody clone is compared.

A Feasibility Study of a Capacitive Biosensor for Direct Detection of DNA Hybridization

This preliminary study was performed to prove the feasibility of a direct capacitive DNA biosensor for detection of nucleic acids. Two different methods for immobilization of the oligonucleotide probes were used. The first type of sensor was composed of a gold rod with a self-assembled monolayer of a 26-base long oligonucleotide probe, modified with an SH-group at the 5 0 -end. Coverage studies showed that only around 20% of the surface was covered, probably due to the bulky nature of the probes. Hybridization studies performed in a flowthrough cell showed selectivity towards a DNA sample containing single stranded fragments of cytomegalo virus (CMV) possessing a complementary sequence. As few as 25 molecules could be detected at sample concentrations of 0.2 attomolar with an injection volume of 250mL. Controls with fragments of double-stranded CMV and single-stranded hepatitis B virus and tyrosinase mRNA gave all lower responses. The other type of sensor was modified by covalent immobilization of a phosphorylated 8-base long oligonucleotide probe to a self-assembled monolayer of cysteamine. This biosensor also showed selectivity against single stranded fragments of CMV and also in this case as few as 25 molecules could be detected.

Surface spectroscopy and electrochemical characterisation of metal dithizonates covalently attached to gold by a self-assembled cysteamine monolayer

Download options Please wait... Article information DOI https://doi.org/10.1039/A708625C Article type Paper Download Citation J. Chem. Soc., Faraday Trans., 1998,94, 1321-1327 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Surface spectroscopy and electrochemical characterisation of metal dithizonates covalently attached to gold by a self-assembled cysteamine monolayer F. Mirkhalaf and D. J. Schiffrin, J. Chem. Soc., Faraday Trans., 1998, 94, 1321 DOI: 10.1039/A708625C To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Fakhradin Mirkhalaf David J. Schiffrin

Electrocatalytical oxidation of NADH with dopamine covalently bound to self-assembled cysteamine monolayers on a gold electrode

The preparation of a gold electrode modified by dopamine covalently bound to self-assembled cysteamine monolayer (dopamine-SAM) is described. The modified electrode exhibits a quasi-reversible surface wave in phosphate buffer (pH 7.0). The charge transfer coefficient and the apparent surface electron transfer rate constant for the redox couple of Q QH 2 at the dopamine-SAM modified electrode are found to be 0.442 and 1.06 s −1, respectively. The electrode shows a drastic enhancement in the oxidation of NADH and a stable electrochemical behavior for high NADH concentration. The anodic overpotential is reduced by ca. 400 mV compared with those obtained at bare gold electrodes. The current response of DPV increases linearly with the NADH concentration from 0.1 mM to 1.0 mM. In addition, it is found that for 2.0 mM NADH, the diffusion coefficient equals to (2.4±0.2) × 10 −6 cm 2 s −1 in 0.05 M phosphate buffer (pH 7.0) containing 0.1 M KCl, and it is in good agreement with previous results.

Electrocatalytic oxidation of NADH at a gold electrode modified by thionine covalently bound to self-assembled cysteamine monolayers

Abstract The preparation of chemically modified gold electrodes by thionine covalently bound to self-assembled cysteamine monolayer (SAM) is described. This thionine-SAM modified electrode is electroactive and exhibits two new electrochemical redox couples with formal potentials which are more positive than that of thionine in bulk solution. An obvious electrocatalytic oxidation of nicotinamine adenine dinucleotide (NADH) is observed; meanwhile, the anodic overpotential is reduced by about 600 mV compared with the results obtained at bare gold electrodes. The participation numbers of H+ for the electroactive SAM are 2 and 1 corresponding to the two electro-couples I and II respectively. The apparent electron transfer rate constant is about 0.02 s−1 at pH 5.0–9.0 for the redox-couple 1. The amperometric response to NADH increased linearly in the range of 2.0 × 10−5 to 1.0 × 10−2 M. The electrolysis results show that the oxidation of NADH is a two-electron process and the product formed is enzymatic active NAD+. In addition, this thionine self-assembled modified electrode shows good stability for long-term use.