Self-assembled Monolayer Technique Research Articles

Osteoblastic early attachment onto the surface of bioadhesive peptide modified pure titanium

To investigate the long-term integrity and the biological function of interface between the bioadhesive peptide modified implant surface and peri-implant tissue. A short bioadhesive peptide containing Glycine-Tyrosine-Arginine-Glycine-Asparticacid-Serine (GYRGDS) sequence was immobilized onto the titanium implant surface by means of sol-gel coating technique and self-assembled monolayers (SAM). The chemical composition and organic functional groups on the titanium surfaces were characterized using XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier transform infrared spectrometer). The adhesive strength and stability of osteoblasts on various implant surfaces were compared under flow condition. The results showed that alkali/hot water aging treatment could apparently improve the content of -OH functional groups of titanium surface. The chemical reactive Ti-O-Ti bonding at the surface of titanium played a vital role in inducing the formation of organosilane SAM. GYRGDS peptide can be covalently grafted onto the surface of titanium by SAM technique. The resistance of freshly adherent osteoblasts to detachment by flow was shear time dependent. When the four groups were compared under the same flow stress condition (2.05 Pa) at three specific time spans (30 min, 1 h, 2 h), the cells retention rates in GYRGDS-grafted groups were 93.0%, 54.4%, 34.4% respectively and were much higher than those in non-coated groups. It was suggested that GYRGDS might have positive effects on maintaining stability and adherence of cells onto the substrates under flow condition.

Development of a DNA Microelectrochemical Biosensor for CEACAM5 Detection

An electrochemical DNA biosensor for the detection of carcinoembryonic antigen-related cell adhesion molecule (CEACAM5), a specific tumor marker for colorectal cancer, is presented. The biosensor based on microelectronicmechanical systems (MEMS) technology, consists of a three electrode configuration where the working electrode is a gold thin-film. The immobilization of the previously designed DNA capture probe is performed by self-assembled monolayer (SAM) technique, and it is hybridized with the complementary target. The formation of the biorecognition surface (SAM) and the detection of the hybridization event are characterized by two different electrochemical techniques: Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV), using potassium ferricyanide/ferrocyanide as redox couple. The differences in the charge transfer resistance (Rct), capacitance (C), and in the redox signals of the potassium ferricyanide/ferrocyanide upon the hybridization, show that the biosensor presented is a rapid, low-cost, and effective tool for CEACAM5 detection. Moreover, the specificity in the hybridization event is demonstrated by exposing the biorecognition surface to a noncomplementary target.

Single-wall carbon nanotube chemical attachment at platinum electrodes

Self-assembled monolayer (SAM) techniques were used to adsorb 4-aminothiophenol (4-ATP) on platinum electrodes in order to obtain an amino-terminated SAM as the base for the chemical attachment of single-wall carbon nanotubes (SWCNTs). A physico-chemical, morphological and electrochemical characterizations of SWCNTs attached onto the modified Pt electrodes was done by using reflection-absorption infrared spectroscopy (RAIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and cyclic voltammetry (CV) techniques. The SWNTs/4-ATP/Pt surface had regions of small, medium, and large thickness of carbon nanotubes with heights of 100–200nm, 700nm to 1.5μm, and 1.0–3.0μm, respectively. Cyclic voltammetries (CVs) in sulfuric acid demonstrated that attachment of SWNTs on 4-ATP/Pt is markedly stable, even after 30 potential cycles. CV in ruthenium hexamine was similar to bare Pt electrodes, suggesting that SWNTs assembly is similar to a closely packed microelectrode array.

Surface plasmon resonance immunosensor for bacteria detection

This work describes an approach for the development of two bacteria biosensors based on surface plasmon resonance (SPR) technique. The first biosensor was based on functionalized gold substrate and the second one on immobilized gold nanoparticles. For the first biosensor, the gold substrate was functionalized with acid–thiol using the self-assembled monolayer technique, while the second one was functionalized with gold nanoparticles immobilized on modified gold substrate. A polyclonal anti- Escherichia coli antibody was immobilized for specific ( E. coli) and non-specific ( Lactobacillus) bacteria detection. Detection limit with a good reproducibility of 10 4 and 10 3 cfu mL −1 of E. coli bacteria has been obtained for the first biosensor and for the second one respectively. A refractive index variation below 5 × 10 −3 due to bacteria adsorption is able to be detected. The refractive index of the multilayer structure and of the E. coli bacteria layer was estimated with a modeling software.

Influence of Cross-linked Waxy Maize Starch on the Aggregation Behavior of Casein Micelles During Acid-induced Gelation

The influence of cross-linked waxy maize starch on the aggregation behavior of casein micelles was investigated using a combination of physico-chemical techniques. Milk was homogenized at two different temperatures (55 and 65 °C) and then heated at 95 °C for 5 min in a pilot scale system. The possible interactions between modified starch and milk proteins during lactic acid fermentation were evaluated. While 1% starch did not show differences in the whey protein complexes formed during heating compared to milk with no starch (as measured by size exclusion chromatography), a higher (2.5%) concentration of starch clearly showed an increased amount of heat-induced whey protein aggregates. The gelation pH also increased significantly with 2.5% starch compared to that of the control samples. The storage modulus (G′) increased with increasing levels of starch, and confocal microscopy confirmed that the microstructure of the casein gels was altered by the presence of modified starch. Milk-starch mixtures preheated and homogenized at 55 or 65 °C exhibited similar physico-chemical behavior during acidification. The results suggested a lack of interaction between starch granules and casein micelles during acidification, and scanning electron microscopy images collected with a self-assembled monolayer technique also confirmed that starch granules were not attached to milk caseins but only embedded in the protein gel matrix.

SURFACE TAILORING OF PTFE FOR ENDOTHELEAL CELLS SELECTIVITY BASED ON POLYDOPAMINE-ASSISTED SELF-ASSEMBLY MONOLAYER TECHNIQUE

An endothelial preferential PTFE was developed via polydopamine-assisted self-assembly monolayer (SAM) technique. XPS,ellipsometer,QCM-D and contact angle data confirmed the self-polymerization process of DOPA and subsequently self-assembly monolayer formation of CGREDVDY. In cell adhesion experiments, both endothelial cells ( ECs) and smooth muscle cells ( SMCs) exhibited improved attachment on DOPA modified PTFE surfaces,but the surfaces did not have noticeable preference between the two cell types. However,after further SAM formation,those surfaces containing bioactive peptides CGREDVDY showed significant selection toward ECs. ECs preferential surface based on such approaches might open another window towards in situ endothelialization in those complex physiological environments in vivo.

BaTiO<sub>3</sub> Functional Ceramics Thin Film Prepared by Self-Assembled Monolayers

BaTiO3 thin film was prepared by the self-assembled monolayers technique and liquid phase deposition. The effects of pH values and the deposition temperature on the formation of BaTiO3 film were studied. The results showed that the Si substrate was in the precursor solution with 0.025mol/L (AHFT/BN/BA=1:1:3) and pH= 1.5. At 45°C deposited for 8h and annealed at 600°C for 2h, the BaTiO3 film with higher crystalline was prepared on the functionalized Si substrate. XRD and SEM tests showed that the film deposited in the precursor solution with different pH values appeared BaTiO3 characteristic peaks on the surface of every crystal. As pH values increased to 1.5 from 0.5, the strength of the film diffraction peak increased. But the width of the peak became smaller and the crystalline increased. When pH value was 2, due to the self-polymerized deposition of [Ti(OH)6]2-, it was easy to form the larger particles on the substrate. When the deposition temperature was 45°C, the acicular BaTiO3 film formed with the regular order and homogeneous planeness on the substrate. When the deposition temperature was between 55°C and 60°C, the dewatering and polymerizing speed between [Ti(OH)6]2- ions was higher than that between [Ti(OH)6]2- and -OH. The adsorption of the film to the Si substrate was weakened. It was easy for the film to fall off.

Quantitative Nanoproteomics for Protein Complexes (QNanoPX) Related to Estrogen Transcriptional Action

We developed an integrated proteomics approach using a chemically functionalized gold nanoparticle (AuNP) as a novel probe for affinity purification to analyze a large protein complex in vivo. We then applied this approach to globally map the transcriptional activation complex of the estrogen response element (ERE). This approach was designated as quantitative nanoproteomics for protein complexes (QNanoPX). In this approach, the positive AuNP-ERE probes were functionalized with polyethylene glycol (PEG), and the consensus sequence of ERE and negative AuNP-PEG probes were functionalized with PEG without the ERE via a thiolated self-assembly monolayer technique. The AuNP-ERE probe had substantially low nonspecific binding and high solubility, which resulted in a 20-fold enrichment of the factor compared with gel beads. In addition, the surface-only binding allows the probe to capture a large protein complex without any restrictions due to pore size. The affinity purification method was combined with MS-based quantitative proteomics and statistical methods to reveal the components of the ERE complex in MCF-7 cells and to identify those components within the complex that were altered by the presence of 17beta-estradiol (E2). Results indicated that a majority of proteins pulled down by the positive probe exhibited significant binding, and approximately one-half of the proteins, including estrogen receptor alpha (ERalpha), were slightly but significantly affected by a 24-h treatment with E2. Based on a combination of bioinformatics and pathway analysis, most of the affected proteins, however, appeared to be related to the transcriptional regulation of not only ERalpha but also c-Myc. Further confirmation indicated that E2 enhanced the ERE binding of c-Myc by 14-fold, indicating that c-Myc may play a major role, along with ERalpha, in E2-mediated transcription. Taken together, our results demonstrated a successful QNanoPX approach toward new pathway discovery and further revealed the importance of cross-interactions among transcription factors.

Thin carbonate apatite layer biomimetically-coated on SAM-Ti substrate surfaces

A self-assembled monolayer (SAM) technique was employed to produce carbonate apatite (CA) coatings onto Ti substrates after sulfonation. The Ti substrates thus treated (S-SAM-Ti) were immersed in metastable calcium phosphate solutions containing carbonate to induce precipitation of carbonate apatite on the surface. The uniformity and homogeneity of the CA layer was partly demonstrated by the XPS crater-edge-line analysis. Both calcium and phosphorus were distributed quite evenly within a layer of approximately 1000 nm.

A microchip fabricated with a vapor-diffusion self-assembled-monolayer method to transport droplets across superhydrophobic to hydrophilic surfaces

A wettability gradient to transport a droplet across superhydrophobic to hydrophilic surfaces is fabricated on combining a structure gradient and a self-assembled-monolayer (SAM) gradient. The combination of these two gradients is realized with a simple but versatile SAM technique, in which the textured silicon wafer strip is placed vertically in a bottle that contains a decyltrichlorosilane solution to form concurrently a saturated SAM below the liquid surface and a wettability gradient above. The platform fabricated in this way has a water-contact angle from 151.2 degrees to 39.7 degrees; the self-transport distance is hence increased significantly to about 9 mm. A theoretical model that approximates the shape of a moving drop to a spheroidal cap is developed to predict the self-transport behavior. Satisfactory agreement is shown for most regions except where the hysteresis effect is unmeasurable and an unsymmetrical deformation occurs. A double-directional gradient surface to alter the direction of movement of a droplet is also realized. The platforms we developed serve not only to transport a fluid over a long distance but also for a broad spectrum of biomedical applications such as protein adsorption, cell adhesion and DNA-based biosensors.

Removal of natural organic matter using self-assembled monolayer technology

The use of nanotechnologies in water treatment for the removal of natural organic matter (NOM) is a relatively new concept. Using simple self-assembled monolayer (SAM) techniques, a silica substrate was modified as an adsorbent and tested for its potential for reduction of water quality parameters such as UV absorbance, colour and dissolved organic carbon (DOC). Silica particles that were coated with an amino-siloxane SAM (NH2-SAM) were evaluated in both a high surface area powder form and also a more realistic granular sand form. Initial results using direct stirred contact with powdered NH2-SAM showed promising results with 60% reduction of UV254 after 1 h and up to 70% removal of DOC with higher doses and contact times. NH2-SAM powder removed NOM in a broader and less selective molecular weight (MW) range than coagulation treatment and this removal was enhanced by pH control at 6, especially for medium MW components. When NH2-SAM sand was applied, the significantly reduced effective surface area resulted in lower DOC removal but colour removal was still considerable for realistic treatment plant contact times. Attempted regeneration with acidic solutions showed greater effectiveness at lower applied pH, however recovery of adsorption capacity reduced with successive adsorption/regeneration cycles highlighting the need for further refinement of operating conditions for more effective application of this relatively simple water treatment technology.

Preparation and Characterization of Tetragonal BaTiO<SUB>3</SUB> Thin Film with Self-assembled Monolayers Technique

Preparation and Characterization of Tetragonal BaTiO<SUB>3</SUB> Thin Film with Self-assembled Monolayers Technique

Tapered optical fiber biosensor for the detection of anti-gliadin antibodies

Abstract A new biosensor has been developed by coating a tapered optical fiber with an anti-gliadin antibodies (AGAs) sensitive nanofilm using the electrostatic self-assembled (ESA) monolayer technique in order to aid the diagnosis of celiac disease. Optical fibers were tapered and then the specific antigen was deposited using the ESA method which allows the construction of nanometric scale recognition surfaces on the fiber optic and helps to create fast response sensors for real time observation of the binding process. Power changes up to 6 dB have been recorded during the antibodies binding process with concentrations in the range 1–15 ppm. Optimal deposition parameters have been selected using an in situ interferometric characterization technique which allows to state the working point of the sensor accurately. The high sensitivity and continuous monitoring of the proposed scheme can reduce importantly the time and serum volume required for celiac disease tests.

A novel sugar-probe biosensor for the deadly plant proteinous toxin, ricin

Because of the illegal use of highly toxic ricin from the castor-oil plant, Ricinus communis, in bioterrorism and suspected white powder cases, anti-terrorism measures for the toxin are urgently required. Here we demonstrate a facile and sensitive detection method using synthetic analogues of β-lactosyl- and β- d-galactosyl ceramides as the ligands based on the fact that ricin binds cell-surface oligosaccharides. Sugar-probes having lipoic acids as anchor functions were synthesized via either a chemical or chemoenzymatic way and were immobilized on the sensor chips by a self-assembled monolayer technique. Surface plasmon resonance (SPR) analysis using these carbohydrate probes allowed us to detect the toxin in a highly sensitive and facile manner (10 pg/mL, 5 min), being the best benchmark as a method for detecting the toxin. In addition, a visual monitoring method was developed, in which sugar-coated Au nanoparticles were utilized for discriminating ricin from other proteins in a facile manner, taking 10–30 min for judgment.

Electrochemical Detection of DNA Hybridization Based on the Probe Labeled with Carbon‐Nanotubes Loaded with Silver Nanoparticles

AbstractA sensitive electrochemical method for the detection of DNA hybridization based on the probe labeled with multiwall carbon‐nanotubes (MWNTs) loaded with silver nanoparticles (Ag‐MWNTs) has been developed. MWNTs were electroless‐plated with a large number of silver nanoparticles to form Ag‐MWNTs. Probe single strand DNA (ss‐DNA) with a thiol group at the 3′‐terminal labeled with Ag‐MWNTs by self‐assembled monolayer (SAM) technique was employed as an electrochemical probe. Target ss‐DNA with a thiol group was immobilized on a gold electrode by SAM technique and then hybridized with the electrochemical probe. Binding events were monitored by differential pulse voltammetric (DPV) signal of silver nanoparticles. The signal difference permitted to distinguish the match of two perfectly complementary DNA strands from the near perfect match where just three base pairs were mismatched. There was a linear relation between the peak current at +120 mV (vs. SCE) and complementary target ss‐DNA concentration over the range from 3.1×10−14 to 1.0×10−11 mol/L with a detection limit of 10 fmol/L of complementary target ss‐DNA. The proposed method has been successfully applied to detection of the DNA sequence related to cystic fibrosis. This work demonstrated that the MWNTs loaded with silver nanoparticles offers a great promising approach for sensitive detection of DNA hybridization.

Evaluation of nano-frictional and mechanical properties of a novel Langmuir–Blodgett monolayer/self-assembly monolayer composite structure

A novel stearic acid (SA)/3-aminopropyltrethoxysilane (APS) composite structure was fabricated using the combined method of the Langmuir–Blodgett technique and self-assembly monolayer (SAM) technique. Its frictional, adhesive properties and interface contact types between the atomic force microscope tip and the samples were evaluated based on Amonton’s laws and the general Carpick’s transition equation, respectively. The results showed that the tip–sample contacts corresponded to the Johnson–Kendall–Robert/Derjaguin–Muller–Toporov (DMT) transition model for SiO2, APS-SAMs, and the unheated SA-APS composite structure, and for the heated SA-APS bilayer to the DMT model. Frictional forces for the four samples were linearly dependent on external loads at higher loads, and at lower loads they were significantly affected by adhesive forces. Frictional and scratching tests showed that the heated SA-APS composite structure exhibited the best lubricating properties and adhesion resistance ability, and its wear resistance capacity was greatly improved due to the binding-mode conversion from hydrogen bonds to covalent bonds. Thus, this kind of composite bilayer might be promising for applications in the lubrication of nano/microelectromechanical systems.

Immobilization of alcohol dehydrogenase on platinum surface by using self-assembly monolayer technique for biofuel cell applications

Immobilization of alcohol dehydrogenase on platinum surface by using self-assembly monolayer technique for biofuel cell applications

Microfluidic systems integrated with two-dimensional surface plasmon resonance phase imaging systems for microarray immunoassay

This study reports a microfluidic chip integrated with an arrayed immunoassay for surface plasmon resonance (SPR) phase imaging of specific bio-samples. The SPR phase imaging system uses a surface-sensitive optical technique to detect two-dimensional (2D) spatial phase variation caused by rabbit immunoglobulin G (IgG) adsorbed on an anti-rabbit IgG film. The microfluidic chip was fabricated by using micro-electro-mechanical-systems (MEMS) technology on glass and polydimethylsiloxane (PDMS) substrates to facilitate well-controlled and reproducible sample delivery and detection. Since SPR detection is very sensitive to temperature variation, a micromachine-based temperature control module comprising micro-heaters and temperature sensors was used to maintain a uniform temperature distribution inside the arrayed detection area with a variation of less than 0.3 °C. A self-assembled monolayer (SAM) technique was used to pattern the surface chemistry on a gold layer to immobilize anti-rabbit IgG on the modified substrates. The microfluidic chip is capable of transporting a precise amount of IgG solution by using micropumps/valves to the arrayed detection area such that highly sensitive, highly specific bio-sensing can be achieved. The developed microfluidic chips, which employed SPR phase imaging for immunoassay analysis, could successfully detect the interaction of anti-rabbit IgG and IgG. The interactions between immobilized anti-rabbit IgG and IgG with various concentrations have been measured. The detection limit is experimentally found to be 1 × 10 −4 mg/ml (0.67 nM). The specificity of the arrayed immunoassay was also explored. Experimental data show that only the rabbit IgG can be detected and the porcine IgG cannot be adsorbed. The developed microfluidic system is promising for various applications including medical diagnostics, microarray detection and observing protein–protein interactions.

Characterization of self-assembled monolayers of iron and cobalt octaalkylthiosubstituted phthalocyanines and their use in nitrite electrocatalytic oxidation

Cobalt and iron phenylthiosubstituted phthalocyanines have been deposited on Au electrode surfaces through the self-assembled monolayer (SAM) technique. The so formed layers were studied using voltammetric and impedance techniques. These SAMs blocked a number of Faradic processes and electrocatalyzed the oxidation of nitrite. The electrocatalytic parameters of the cobalt and iron phenylthiosubstituted phthalocyanines deposited on Au electrodes in nitrite solution were studied. Nitrite overpotentials which are lower than ever reported were obtained in this work for the iron phenylthiosubstituted phthalocyanines with very high stability.

Comparative electrooxidation of sulphite by self-assembled monolayers (SAMs) of Co(II), Fe(II), Ni(II) and Mn(III) tetrakis benzylmercapto and dodecylmercapto metallophthalocyanines complexes on gold electrodes

This work reports on the use of Co(II), Fe(II), Mn(III) and Ni(II) tetrakis benzylmercapto and dodecylmercapto phthalocyanine complexes for gold electrode modification for electrooxidation of sulphite ions. The complexes were successfully used to modify gold electrodes by self-assembled monolayer (SAM) technique. The self-assembled films are stable and showed blocking characteristics towards the following Faradaic processes; gold surface oxidation, underpotential deposition (UPD) of copper and solution redox chemistry of [Fe(H(2)O)(6)(3+)]/[Fe(H(2)O)(6)(2+)]. All the modified electrodes showed improved catalytic activities than the unmodified gold electrode towards sulphite ion electrooxidation with all the modified electrodes exhibiting high resistance to electrode surface passivation. Better catalytic performance were obtained for the CoPcs, FePcs and MnPcs which have metal based redox processes within the range of the sulphite electrooxidation peak, while the NiPcs which did not show metal based redox reaction performed less. The catalytic current was found to be linear with sulphite ion concentration in the concentration range employed in this work (0.1-1mM) and sensitivities ranging from 1.68 to 2.96muA/mM were observed for all the modified electrodes. Mechanisms of the catalytic oxidation of sulphite ions are proposed.