Characterization of the substructure and properties of immobilized peptides on silicon surface

Immobilization of biomaterials onto solid supports is a means of functionalizing materials for applications such as biosensing. Biologically active peptide (A-A-A-A-G-G-G-E-R-G-D)¹ films were attached to N-hydroxy succinimide ester terminated self-assembled monolayers (SAM) which were covalently linked to a smooth silicon surface via Si–C bonds. The peptide films were characterized using electrical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The film structures were determined from examination of the capacitance and conductance dispersions with frequency. Analysis of XPS, EIS and FTIR after immobilization of the peptide film at pH 4 and 7 provided information on the extent of the activation and overall coupling efficiencies of the peptides to the N-hydroxy succinimide ester surface. The resulting film structure was markedly altered by attachment of the peptide at pH 4.     

Patterning of ITO films on flexible substrates by using self-assembled monolayer

The patterning of indium tin oxide (ITO) films on flexible polyester (PET) substrates by using a self-assembled monolayer (SAM) of octadecyltrimethoxysilane (OTMS) was investigated. After a SAM is deposited on ITO films, the ITO surface hydrophilicity and electron transfer characteristics are altered. The contact angle and electrochemical cyclic voltammetry analyses indicate the optimal process to form a SAM on ITO films operated in a low-humidity environment at 25 ºC for 24 h. The AFM observation shows that the ITO films covered by a SAM can be protected during etching in an oxalic solution, which means a SAM can well play the role of a photoresist during lithographic process.     

Growth and patterning of pt nanowires on silicon substrates

This paper describes a simple procedure for growing dense films of Pt nanowires directly on silicon substrates by modifying the surface through chemical or physical means. In the former, a self-assembled monolayer of (3-mercaptopropyl)-trimethoxysilane (MPTMS) is applied which can strongly bind Pt(0) nuclei to the surface through Pt S linkages. Once attached, the Pt(0) nuclei can act as catalytic sites for the growth of Pt nanowires along the 〈111〉 direction. Alternately, relief features are physically created on the surface in order to generate nucleation and binding sites for Pt(0) nuclei, due to the higher free energy associated with a rough surface. Additionally, Pt nanowires have been successfully produced in well-defined patterns by scouring grooves on the silicon surface or by photochemically patterning the MPTMS monolayers with a shadow mask. We have also measured the electrochemical properties of these immobilized or patterned Pt nanowires. The results provide an effective route to producing dense films of Pt nanowires with high surface areas for various electrochemical applications.     

The self-assembled monolayer of saccharide via click chemistry: Formation and protein recognition

We prepared the saccharide-immobilized substrate via click chemistry. The azide-terminated saccharides were reacted by a facile metathesis reaction. The density of saccharides was controlled by the incubation time of SAM preparation. The saccharide-protein interaction was analyzed using the saccharide substrate. The interaction of the saccharide substrate with protein was strong and specific due to the glyco-cluster effects. The interaction with amyloid β was analyzed by the monosaccharide-immobilized substrate, and the sulfonated saccharides showed strong interaction.     

Low density lipoprotein sensor based on surface plasmon resonance

Biotinylated heparin has been immobilized onto self-assembled monolayer of 4-aminothiophenol using avidin–biotin specific binding. The modified electrodes have been characterized using surface plasmon resonance technique (SPR), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM) and contact angle (CA) measurements. The interaction of immobilized biotinylated heparin with low density lipoprotein (LDL) has been studied using surface plasmon resonance technique. The biotinylated heparin modified electrode can be used to detect LDL in the range of 20 to 100 mg/dl with the sensitivity of 513.3 m°/μM.     

Impact of surface modification by addition of self-assembled monolayer for carrier transport of quaterrylene thin films

Quaterrylene field-effect transistors (FETs) were formed on a silicon oxide (SiO₂) layer and on an octadecyltrichlorosilane self-assembled monolayer (OTS-SAM). To elucidate the transport mechanisms in the respective devices, we examined the dependence of carrier mobility on film thickness and temperature. On the OTS surface, a marked increase in the carrier mobility was observed in the initial layers, indicating that the accumulated carriers were distributed closer to the interface than were those on the SiO₂ surface. Moreover, the carrier transport in the respective devices exhibited distinct behaviors in the low temperature range, particularly in the initial layers. On the SiO₂ surface the carrier mobility depended strongly on temperature; the value drastically declined with the decreasing temperature from 300 K down to 60 K. On the OTS surface, the carrier mobility showed temperature-independent transport below 210 K. This maintenance of the carrier transport at low temperatures was caused by the termination of the trap-state density near the interface. These results clearly reveal that the OTS treatment effectively helped improve the interface properties because of a reduction in the density of the carrier traps, dramatically facilitating the carrier transport in the initial layers.     

A vapor phase deposition of self-assembled monolayers: Vinyl-terminated films of volatile silanes on silicon oxide substrates

Vinyl-terminated self-assembled monolayers (SAMs) offer significant flexibility for further chemical modification and can serve as a versatile starting point for a tailoring of surface properties. A vapor phase deposition of such films would offer advantages in cases where the preparation from solution is not an option or not desired, for example in connection with silicon microstructures such as micro-electromechanical systems. We show that SAMs of 9-decenyltrichlorosilane (CH₂CH(CH₂)₈SiCl₃), 10-undecenyltrichlorosilane (CH₂CH(CH₂)₉SiCl₃), 14-pentadecenyltrichlorosilane (CH₂CH(CH₂)₁₃SiCl₃), decyltrichlorosilane (CH₃(CH₂)₉SiCl₃), and octadecanetrichlorosilane (CH₃(CH₂)₁₇SiCl₃) can be prepared both from solution and from the vapor phase. The resulting layers were compared by static contact angle measurements, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy to determine their surface wettability, the film thickness, the smoothness and homogeneity of the respective films, and their chemical composition and each method gave films of comparable quality. Deposition of functionalized SAMs from the vapor phase is rare. Here we report the parameters for the preparation of well-ordered vinyl-terminated SAMs from the vapor phase.     

The adhesive properties of pyridine-terminated self-assembled monolayers

The atomic force microscopy (AFM) adhesion force behaviour and contact angle titration behaviour of self-assembled monolayers (SAMs) presenting surface pyridine and substituted pyridine moieties has been investigated as a function of pH and electrolyte concentration. The pK_as of the pyridine moieties were modified through the incorporation of fluorine, chlorine and bromine substituents in the pyridyl ring. Contact angle titration and AFM adhesion force measurements were performed using aqueous phosphate buffered saline solutions over the pH range 3-9, and at concentrations of 150 mM and 0.1 mM. AFM adhesion force measurements were performed using a clean Si₃N₄ pyramidal-tipped AFM cantilever.     

Significantly improved stability of n-octadecyltrichlorosilane self-assembled monolayer by plasma pretreatment on mica

It has been well known that plasma pretreatment can stabilize the hydrocarbon silane monolayer self-assembled on a mica surface. However, the extent of this improvement is not well known. To explore this issue, n-octadecyltrichlorosilane (OTS) monolayers were self-assembled on both untreated and plasma-treated mica surfaces, and their interfacial properties were investigated and compared at various physical conditions (temperature, relative humidity, contact time, high stress, and contact repetition) through the use of surface force measurements. This study revealed that in highly humid conditions (> 90% relative humidity) there is a substantial difference of stability between untreated and plasma-treated surfaces, the OTS monolayer on plasma-treated mica surface being much more stable. In particular, protrusion behavior in the monolayer was always observed in untreated samples, but never in plasma-treated samples during contact repetition experiments. This directly demonstrates that the significantly improved stability directly comes from extensive chemical bonds between OTS molecules and the plasma-treated mica surface.     

Cyclic voltammetry on n-alkylphosphonic acid self-assembled monolayer modified large area indium tin oxide electrodes

We show stable bonding of n-alkylphosphonic acid self-assembled monolayers (SAMs) to indium tin oxide electrodes and their direct electrical characterization by cyclic voltammetry (CV). The functional coatings were investigated with regards to the addressability and stability of the electrodes, which are related to small changes in molecular layer thickness. The response of a redox active compound in solution to the faradic current is indirectly proportional to the molecular chain length of the SAMs. We observed a decrease of the electrode sensitivity with enhanced surface protection and slow long term degradation of the SAM under electrochemical stress by CV, and therefore conclude a trade-off optimum for molecules with the C10 chain.     

Effects of interfacial modification on the performance of an organic transistor based on TCNQ LB films

The influence of interfacial modifications of n-type organic-based thin-film transistors (OTFTs), using low work-function metal electrodes and self-assembled monolayers (SAMs), were analyzed by electrical and structural measurements. We employed ultra thin films of long-alkyl-chained tetracyanoquinodimethane (C₁₈-TCNQ) Langmuir-Blodgett (LB) films as the n-type semiconducting layer with nano-scale thickness. A significant increase in the drain current was observed for the OTFT with low work-function metal electrodes, and this current increase was consistent with the decrease in the injection barrier height for carrier electrons to transfer from the electrodes into the LB films. On the other hand, it was found that the density of interfacial trapping sites decreased with the SAMs treatment, even though no structural modification was induced by the SAM. This behavior is considered to be due to the elimination of active SiOH groups on the SiO₂ substrate by the SAMs treatments. It was also found that the device parameters strongly depend on the alkyl chain length of the SAMs. In order to explain this phenomenon clearly, a new interfacial model based on the interaction between carrier electrons and interfacial SiOH groups is proposed.     

Enhanced thermal stability of laccase immobilized on monolayer-modified nanoporous Au

Nanoporous Au was fabricated by the dealloying of Au-Ag alloy in nitric acid, and was modified with a self-assembled monolayer (SAM) of 4-aminothiophenol, for the enhancement of high-temperature activity of immobilized laccase. Immobilized laccase exhibited much higher activity than that of free laccase at > 45 °C. SAM surface modification greatly improved the thermal stability and reusability of immobilized laccase. For example, little degradation in laccase activity when immobilized on SAM-modified nanoporous Au was observed after 2 h incubation at 50 °C. This suggested the nanoporous structure and SAM synergistically prevented the conformational change of laccase, and resulted in the enhancement of high-temperature activity.     

Immobilization of aromatic aldehyde molecules on indium tin oxide surface using acetalization reaction

We demonstrated an acetalization reaction as a versatile method to immobilize aromatic aldehyde molecules on surfaces of metal oxides, silicon dioxide, and indium tin oxide. First, a trimethylsily (TMS) terminated surface was formed using a silylation reaction between a chloride group of trimethylsilychloride and a hydroxyl group of the substrate surfaces. Second, terephthalaldehyde (TPA) was immobilized on the surfaces using an acetalization reaction between the TMS-terminated surface and an aldehyde group of TPA. Results of contact angle, X-ray photoelectron, and ultraviolet absorption spectra revealed that the TPA molecules on the surfaces were well-packed with a high surface density.     

Influence of surface chemistry on inkjet printed carbon nanotube films

Carbon nanotube ink chemistry and the proper formulation are crucial for direct-write printing of nanotubes. Moreover, the correct surface chemistry of the self-assembled monolayers that assist the direct deposition of carbon nanotubes onto the substrate is equally important to preserve orientation of the printed carbon nanotubes. We report that the successful formulation of two single walled carbon nanotube (SWNT) inks yields a consistent, homogenous printing pattern possessing the requisite viscosities needed for flow through the microcapillary nozzles of the inkjet printer with fairly modest drying times. The addition of an aqueous sodium silicate allows for a reliable method for forming a uniform carbon nanotube network deposited directly onto unfunctionalized surfaces such as glass or quartz via inkjet deposition. Furthermore, this sodium silicate ingredient helps preserve applied orientation to the printed SWNT solution. Sheet resistivity of this carbon nanotube ink formula printed on quartz decreases as a function of passes and is independent of the substrate. SWNTs were successfully patterned on Au. This amine-based surface chemistry dramatically helps improve the isolation stabilization of the printed SWNTs as seen in the atomic force microscopy (AFM) image. Lastly, using our optimized SWNT ink formula and waveform parameters in the Fuji materials printer, we are able to directly write/print SWNTs into 2D patterns. Dried ink pattern expose and help orient roped carbon nanotubes that are suspended in ordered arrays across the cracks.     

Preparation and atomic force microscopy observation of lipid membranes on micro-patterned self-assembled monolayers

Using micro-contact printing (μCP) method, lipid membranes were deposited on the surface of micro-patterned self-assembled monolayers. Height and phase mode atomic force microscopy (AFM) images showed that the resulting deposited films were flat and that a micro-patterned composite bilayer system was constructed. It was also shown that the use of crystalline phase lipid membrane is effective for the preparation of the micro-patterned composite bilayer system of membranes with flat surface.     

Study on the solid state reaction between bilayered Pd/Au films and silicon substrates

Bilayers of pure palladium and gold films were evaporated alternatively on (1 0 0) and (1 1 1) monocrystalline silicon substrates. After annealing, in a vacuum furnace from 100 to 650 °C during 30 min, the growth sequence of the Pd₂Si and PdSi phases that evolved as the result of the diffusion reaction was examined by means of Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), whereas the surface morphology was investigated by scanning electron microscopy (SEM) technique. The effect of the intermediate gold layer is investigated in order to test its effectiveness as barrier for Cu and Si atoms interdiffusion and its influence on the morphology of the formed palladium silicides. The effect of substrate orientation on the palladium silicides growth and formation was also explored.     

3D,Reconfigurable, Multimodal Electronic Whiskers via Directed Air Assembly

A batch‐assembly technique for forming 3D electronics on shape memory polymer substrates is demonstrated and is used to create dense, highly sensitive, multimodal arrays of electronic whiskers. Directed air flow at temperatures above the substrate's glass transition temperature transforms planar photolithographically defined resistive sensors from 2D precursors into shape‐tunable, deterministic 3D assemblies. Reversible 3D assembly and flattening is achieved by exploiting the shape memory properties of the substrate, enabling context‐driven shape reconfiguration to isolate/enhance specific sensing modes. In particular, measurement schemes and device configurations are introduced that allow for the sensing of temperature, stiffness, contact force, proximity, and surface texture and roughness. The assemblies offer highly spatiotemporally resolved, wide‐range measurements of surface topology (50 nm to 500 µm), material stiffness (200 kPa to 7.5 GPa), and temperature (0–100 °C), with response times of <250 µs. The development of a scalable process for 3D assembly of reconfigurable electronic sensors, as well as the large breadth and sensitivity of complex sensing modes demonstrated, has applications in the growing fields of 3D assembly, electronic skin, and human–machine interfaces.     

Sensing properties of two-component Langmuir-Blodgett layer and its porous derivative in SAW sensor for vapors of methanol and ethanol

Two-component Langmuir-Blodgett film has been fabricated from equimolar mixture of 5-[[1,3-dioxo-3-[4-(1-oxooctadecyl)phenyl]propyl]amino]-1,3-benzenedicarboxylic acid with cetylamine. Porous one-component derivative of this film has been obtained by removing of cetylamine. Both films have been investigated as sensing layers of the surface acoustic wave sensors for vapors of methanol and ethanol in air. These films react on the alcohol vapors. Time of the sensor reaction is less than 2 s and this reaction is reversible. The response parameters of the sensor depend on the kind of the alcohol and the structure of the layer. An explanation of the observed differences in the behavior of both layers in contact with vapors of the alcohols has been proposed.     

Coating of collagen on a poly(l-lactic acid) sponge surface for tissue engineering

Porous scaffolds play important roles in tissue engineering. Biodegradable synthetic polymers, such as poly(l-lactic acid) (PLLA), frequently are used in the preparation of porous scaffolds. Pretreating the surface of a PLLA porous scaffold is required to increase its wettability for smooth cell seeding due to the hydrophobic property of the scaffold's surface. In this study, a simple coating method was used to modify the surface of the PLLA sponges. The coating method included three steps: filling the PLLA sponge pores with collagen aqueous solution, centrifuging to remove excess collagen, and, finally, freeze-drying. Compared with the uncoated PLLA sponge, the collagen-coated PLLA sponge demonstrated both improved wettability and high water absorption. Cells were smoothly seeded in the collagen-coated PLLA sponges by dropping a cell suspension solution onto the sponges. Cells adhered to the collagen-coated sponge and were distributed homogeneously throughout the collagen-coated PLLA sponge.