Periodic ZnO nanorod arrays defined by polystyrene microsphere self-assembled monolayers

We demonstrate a low-cost and effective method to fabricate hexagonally patterned, vertically aligned ZnO nanorod arrays. Selective wet-etching is used to develop the catalyzing gold particle hexagonal pattern with the aid of a polystyrene microsphere self-assembled monolayer. The gold particles have tunable sizes independent of the polystyrene microsphere's diameter and are inherently round in shape. Each ZnO rod is grown individually from a catalyzing site via catalyst-initiated epitaxy, and the original hexagonal periodicity is well-preserved. The rods have flat ends, and the diameters of the rods can be controlled well by the amount of source materials. This method provides a promising way to create ZnO one-dimensional nanostructures for applications as two-dimensional photonic crystal, sensor arrays, nanolaser arrays, and optoelectronic devices.     

Inkjet printed electrode arrays for potential modulation of DNA self-assembled monolayers on gold

In this paper, we report a novel and cost-effective fabrication technique to produce electrode arrays that can be used for monitoring and electrical manipulation of the molecular orientation of DNA self-assembled monolayers (SAMs) on gold. The electrode arrays were prepared from gold coated glass sides or compact discs (CD-Rs) by using standard office inkjet printers without any hardware or software modifications. In this method, electrode arrays of varied shape and size (from submillimeter to centimeter) can be rapidly fabricated and are suitable for standard electrochemical measurements. We were able to use a dual-channel potentiostat to control the electrodes individually and a fluorescence (FL) scanner to image the electrode array simultaneously. With such an integrated modulation setup, the structural switching behavior (from "lying" to "standing" position) and the enhanced hybridization reactivity of thiolate DNA SAMs on gold under potential control have been successfully demonstrated.     

Nanopatterned self-assembled monolayers

We report on the fabrication of chemically nanopatterned gold surfaces by combining electron-beam lithography with gas and liquid phase thiolization. The line-edge roughness of the patterns is ～4?nm, corresponding to a limiting feature size in the range of 15?nm. Indications for a lower packing density of the self-assembled monolayers grown in the nanofeatures are given, and evidences for the bleeding of thiols along the grain boundaries of the gold substrate are displayed. A comparison is provided between nanopatterned thiol and silane monolayers on gold and on silicon wafers, respectively. The line-edge roughnesses are shown to be close to each other for these two systems, indicating that the limiting step is currently the lithography step, suggesting possible improvement of the resolution. The advantages and drawbacks of thiol versus silane monolayers are finally discussed with respect to the formation of chemically nanopatterned surfaces.     

Resonance Raman evidence of immobilization of laccase on self-assembled monolayers of thiols on Ag and Au surfaces

Resonance Raman (RR) and surface-enhanced Raman scattering (SERS) spectroscopy have been used to study immobilization of laccase on self-assembled monolayers (SAMs) of thiols containing carboxylic and amino groups, deposited on silver and gold electrodes. A new, indirect way of monitoring laccase bound to the thiol-coated Ag and Au surfaces is presented. It was demonstrated that by recording the resonance Raman spectra of the colored product of the oxidation of syringaldazine (4-hydroxy-3,5-dimethoxybenzaldehydeazine) by laccase in the presence of molecular oxygen, one may easily confirm binding as well as enzymatic activity of laccase immobilized on the SAMs modified silver and gold surfaces.     

Forming microstructured alkanethiol self-assembled monolayers on gold by laser ablation

A process to form microstructured alkanethiol self-assembled monolayers (SAMs) on gold is described. It is well known that alkanethiols spontaneously form homogenous SAMs on gold surfaces. By means of laser ablation, the exposed areas of alkanethiol monolayers can be removed from the gold surface. Free gold is obtained which can react further with second and third thiols. By this technique, structured alkanethiol SAMs are obtained reliably and easily. In a rather narrow window of pulse intensities, in our example 120$hboxMW/cm^2pm hbox10%$from a frequency-doubled Nd : YVO$_4$laser with 6-ns pulsewidth operating at a repetition rate of 20 kHz, ablation of alkanethiol monolayers is obtained without causing any damage to the gold substrate. Examples are presented where lines down to 10$muhbox m$in width were laser ablated into an SAM formed either from a hydrophilic or a hydrophobic alkanethiol and filled with a monolayer of a second alkanethiol of opposite hydrophilicity. The patterned structures were examined by optical and fluorescence microscopy as well as by lateral force microscopy. The presented method enables the preparation of microstructured SAMs on gold and probably on a wide variety of other substrates.     

DNA directed protein immobilization on mixed ssDNA/oligo(ethylene glycol) self-assembled monolayers for sensitive biosensors

A stable and versatile biosensor surface is prepared by site-directed immobilization of protein-DNA conjugates onto a mixed self-assembled monolayer (SAM) composed of ssDNA thiols and oligo(ethylene glycol) (OEG) terminated thiols. The protein conjugates consist of an antibody chemically linked to a ssDNA target with a sequence complementary to the surface-bound ssDNA probes and are immobilized on the surface via sequence-specific hybridization. Compared to standard antibody immobilization techniques, this approach offers many advantages. The exceptional specificity of DNA hybridization combined with the diversity of potential sequences makes this platform perfect for multichannel sensors. Once a surface is patterned with the appropriate probe sequences, sequence-specific hybridization will sort out the target conjugates and direct them to the appropriate spots on the surface. In addition, the DNA SAMs are very stable and well suited to recycling by dehybdridization of the conjugates from the surface-bound probes. In this work, we demonstrate the specificity, sensitivity, and convenience of using protein-DNA conjugates to convert a DNA/OEG SAM surface into a biosensor surface and apply this platform to the detection of human chorionic gonadotropin using surface plasmon resonance.     

Photo-deprotection patterning of self-assembled monolayers

Photo-deprotectable self-assembled monolayers (SAMs) provide a versatile platform for creating functional patterned surfaces. In this study, we present nanoscale photo-patterning, multi-component patterning, and a method for producing molecular gradients using photo-deprotectable SAMs. Nanoscale patterning of photo-deprotectable SAMs was achieved by coupling a UV laser (365 nm) through a scanning near field probe to produce nanoscale lines of ～40 nm, i.e. λ/9. Multi-component patterning was achieved by a two-stage method combining both microcontact printing and soft-UV photo-patterning. The example demonstrated in this study produced a three-component patterned surface with regions of CF₃, CH₃ and COOH/CF₃ functionality. The versatility of these photocleavable SAMs is further demonstrated by creating linear molecular gradients of two functionalities along a distance of ～25 mm. The use of ‘soft’ UV gives several advantages including the ability to pattern SAMs with micron-scale features over large areas quickly, with greater control over the photochemical reactions, and compatibility with existing lithographic facilities thus offering an effective alternative to other patterning methods such microcontact-printing or deep UV patterning.     

CdS纳米粒子的LB膜自组装研究

采用杯[8]衍生物的LB膜成功制备了尺寸可控的CdS纳米微粒.并用AFM、吸收谱、PL谱对其表面形貌和光学性能进行了研究.吸收谱表明循环1次时CdS纳米粒子的吸收边为425nm,这个值同体材料的520nm相比发生了明显的蓝移.随着循环次数的增加,CdS纳米粒子的吸收边逐渐红移,当循环3次时,其吸收边已经移到475nm,这表明纳米粒子的粒径在逐渐长大.CdS纳米粒子的PL谱表明,随着循环次数的增加,其发射峰值逐渐红移,这可能是由于量子尺寸效应造成的.     

Local modification of self-assembled monolayers by a photocatalytic probe

We demonstrate a novel nanolithography method based on the photocatalytic decomposition of the self-assembled monolayer (SAM) near a TiO2-coated probe. The TiO2 film was deposited on Ti-Pt coated Si probes by plasma sputtering. After annealing at 500 degrees C in air for 2 hr, the film was in the anatase phase, according to examination by Raman and X-ray diffraction spectra. Island-structured octadecyltrichlorosilane (OTS) partial monolayers on glass were used as the substrates. When the photocatalytic probe was illuminated by ultra-violet light, the modification occurred on the near OTS SAM islands. No change was observed on the exposed oxide surface between OTS islands. Without UV illumination, no modification occurred on OTS. Thus, the modification of the OTS surface is related to the photocatalytic reaction. A line width as small as 60 nm was achieved and observed by lateral force microscopy (LFM). The diffusion of reactive oxygen species were also observed from the remote photodecomposition of the OTS monolayer. These results should be beneficial to the development of hierarchically constructed nanolithography.     

Carbohydrate-protein interactions by "clicked" carbohydrate self-assembled monolayers

A Huisgen 1,3-dipolar cycloaddition "click chemistry" was employed to immobilize azido sugars (mannose, lactose, alpha-Gal) to fabricate carbohydrate self-assembled monolayers (SAMs) on gold. This fabrication was based on preformed SAM templates incorporated with alkyne terminal groups, which could further anchor the azido sugars to form well-packed, stable, and rigid sugar SAMs. The clicked mannose, lactose, and alpha-Gal trisaccharide SAMs were used in the analysis of specific carbohydrate-protein interactions (i.e., mannose-Con A; ECL-lactose, alpha-Gal-anti-Gal). The apparent affinity constant of Con A binding to mannose was (8.7 +/- 2.8) x 10(5) and (3.9 +/- 0.2) x 10(6) M(-1) measured by QCM and SPR, respectively. The apparent affinity constants of lactose binding with ECL and alpha-Gal binding with polyclonal anti-Gal antibody were determined to be (4.6 +/- 2.4) x 10(6) and (6.7 +/- 3.3) x 10(6) M(-1), respectively by QCM. SPR, QCM, AFM, and electrochemistry studies confirmed that the carbohydrate SAM sensors maintained the specificity to their corresponding lectins and nonspecific adsorption on the clicked carbohydrate surface was negligible. This study showed that the clicked carbohydrate SAMs in concert with nonlabel QCM or SPR offered a potent platform for high-throughput characterization of carbohydrate-protein interactions. Such a combination should complement other methods such as ITC and ELISA in a favorable manner and provide insightful knowledge for the corresponding complex glycobiological processes.     

Biomimetic synthesis of enamel-like hydroxyapatite on self-assembled monolayers

Hydroxyapatite (HAp) crystals mimicking tooth enamel in chemical composition and morphology were formed on sulfonic-terminated self-assembled monolayer (SAM) in 1.5SBF with F⁻ at 50 °C for 7 days. F⁻ ions showed a marked effect on the composition and morphology of deposited HAp crystals. In the absence of F⁻ ions, HAp containing CO₃²⁻ were formed on SAM, and worm-like crystals of 200–300 nm in length aggregated to form a spherical morphology. When F⁻ was added, HAp crystals containing both CO₃²⁻ and F⁻ were formed on SAM. Needle-shaped crystals of high aspect ratio and 1–2 μm in length grew elongated along the c-axial direction. In addition, these needle-shaped crystals grew in bundles, mimicking HAp crystals in tooth enamel. After the process of ripening, the needles in bundle grew to large size of up to 10 μm in length, and still kept no crystal–crystal fusion like enamel HAp crystals. The formation of enamel-like HAp can be attributed to the substitute of F⁻ for OH⁻ by disturbing the normal progress of HAp formation on SAM. The results suggest potential applications in preparing a novel dental material by a simple method.     

Modeling organic surfaces with self-assembled monolayers

The interfacial properties of organic materials are of critical importance in many applications, especially the control of wettability, adhesion, tribology, and corrosion. The relationships between the microscopic structure of an organic surface and its macroscopic physical properties are, however, only poorly understood. This short review presents a model system that has the ease of preparation and the structural definition required to provide a firm understanding of interfacial phenomena. Long-chain thiols, HS(CH₂)_nX, adsorb from solution onto gold and form densely packed, oriented monolayers. By varying the terminal functional group, X, of the thiol, organic surfaces can be created having a wide range of structures and properties. More, complex systems can be constructed by coadsorbing two or more thiols with different terminal functional groups or with different chain lengths onto a common gold substrate. By these techniques, controlled degrees of disorder can be introduced into model surfaces. We have used these systems to explore the relationships between the microscopic structure of the monolayers on a molecular and supramolecular scale and their macroscopic properties. Wettability is a macroscopic interfacial property that has proven of particular interest.     

Subwavelength surface-relief gratings fabricated by microcontact printing of self-assembled monolayers

We have designed and tested subwavelength diffractive optical elements consisting of surface-relief gratings made by microcontact printing of self-assembled monolayers. The first device is a beam deflector for 1.55-mum operation consisting of a surface-relief grating made up of eight pillars over one period (9.3 mum) of the grating. The widths of the pillars vary to approximate a linear phase profile within each grating period. The second device is a quarter-wave plate for 632.8-nm operation consisting of a subwavelength surface-relief grating with a 300-nm period and 58% duty cycle.     

Microstructured bioreactive surfaces: covalent immobilization of proteins on Au(1 1 1)/silicon via aminoreactive alkanethiolate self-assembled monolayers

Micrometer-scale patterns of a defined surface chemistry and structure were produced on both ultraflat Au(1 1 1) and on gold-coated monocrystalline silicon surfaces by a method combining microcontact printing, wet chemical etching and the replacement of etch-resist self-assembled monolayers (SAMs) by functionalized or reactive SAMs. Key steps in this methodology were characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry and contact angle measurements. The covalent immobilization of (functional) biological systems on these surfaces was tested using an N-hydroxysuccinimide ester -functionalized disulphide (DSU), which covalently binds primary amines without the need for further activation steps. Atomic force microscope images of native collagen V single molecules immobilized on these patterned surfaces revealed both high spatial resolution and strong attachment to the monolayer/gold surface. Microcontact printing of DSU is shown to be feasible on specially prepared, ultraflat Au(1 1 1) surfaces providing a valuable tool for scanning probe experiments with biomolecules. The retention of enzymatic activity upon immobilization of protein was demonstrated for the case of horseradish peroxidase. The described approach can thus be used to confine biological activity to predetermined sites on microstructured gold/silicon devices – an important capability in biomedical and biomolecular research. © 1999 Kluwer Academic Publishers     

Site-selective assembly of quantum dots on patterned self-assembled monolayers fabricated by laser direct-writing

A simple and efficient route for quantum dot (QDs) patterning using self-assembled monolayers (SAMs) as templates is described. By means of a laser direct-writing (LDW) technique, SAMs of octadecylphosphonic acid formed by adsorption on native oxide layer of titanium film were patterned through laser-induced ablation of the SAM molecules. This technique allows the creation of chemical-specific patterns accompanied by slight change in the topography. Using atomic force microscopy and friction force microscopy, the dependence of feature size and characteristics on the irradiation dose was demonstrated. Upon immersion of a substrate with patterned SAMs bearing thiol as the terminal group into a dispersion of QDs resulted in the assembly of QDs on the specific thiol-terminated areas. Patterns of QDs with different photoluminescent wavelength were generated. The LDW technique, which is convenient and flexible due to its path-directed and maskless fabrication process, provided a new powerful approach for patterning materials on surfaces for various applications.     

Immobilization of methylene blue on self-assembled iodine monolayers on gold

The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical techniques, scanning tunneling microscopy (STM), Auger Electron Spectroscopy (AES), and Raman spectroscopy. Results show that MB species are efficiently adsorbed on the square root of 3 x square root of 3 R30 degrees I lattice on Au(111). The electrochemical behavior of the adsorbed MB molecules is reversible, indicating a relatively fast electron transfer from the Au(111) surface to the immobilized MB species through the iodine layer. STM images with molecular resolution are consistent with adsorption of MB dimers on a square root of 3 x square root of 3 R30 degrees I lattice placed atop of the Au(111) substrate. Results are compared to those obtained for MB immobilized on Au(111) covered by S(n) (n = 3-8) surface structures.