Microfluidic Devices Containing ZnO Nanorods with Tunable Surface Chemistry and Wetting-Independent Water Mobility.

Interest in polydimethylsiloxane (PDMS) microfluidic devices has grown dramatically in recent years, particularly in the context of improved performance lab-on-a-chip devices with decreasing channel size enabling more devices on ever smaller chips. As channels become smaller, the resistance to flow increases and the device structure must be able to withstand higher internal pressures. We report herein the fabrication of microstructured surfaces that promote water mobility independent of surface static wetting properties.

Functionalized Self-Assembled Monolayers Bearing Diiminate Complexes Immobilized through Covalently Anchored Ligands.

The application of synthetic organic chemistry to the surface chemistry of monolayer arrays adds a novel dimension to the power of these systems for surface modification. This paper describes the elaboration of simple functionalized monolayers into dialdimine and dialdiminate ligands tethered to the monolayer surface. These ligands are then used to coordinate metal ions in an effort to form diiminate complexes with control over their environment and orientation.

An off-the-shelf integrated microfluidic device comprising self-assembled monolayers for protein array experiments.

Microfluidic-based protein arrays are promising tools for life sciences, with increased sensitivity and specificity. One of the drawbacks of this technology is the need to create fresh surface chemistry for protein immobilization at the beginning of each experiment. In this work, we attempted to include the process of surface functionalization as part of the fabrication of the device, which would substitute the time consuming step of surface functionalization at the beginning of each protein array experiment.

Effect of α-Heteroatoms on the Formation of Alkene-Derived Monolayers on H-Si(111): A Combined Experimental and Theoretical Study.

We investigate herein whether the reactivity and surface coverage of 1-alkenes toward hydrogen-terminated Si(111) surfaces [H-Si(111)] can be improved by introducing heteroatoms such as oxygen and sulfur at the α-position next to the alkene functional group. To this end, the reactivity of 1-pentene, 1-pentyne, vinyl ethyl ether, and vinyl ethyl sulfide toward H-Si(111) and the surface coverage of the resulting monolayers were studied and compared. All modified surfaces were characterized by static water contact angle measurements, ellipsometry, X-ray photoelectron spectroscopy (XPS), and infrared absorption reflection spectroscopy (IRRAS).

Carboxylic acid decorated self-assembled monolayer films: new acid synthesis chemistry and reaction chemistry including bridged diacyl peroxide preparation.

Interfacial chemical transformations are an important way to control the physical and chemical properties of surfaces. Organic molecules that self-assemble into monolayers are a proven, effective tool for surface modification, and the ability to do controlled chemical transformations on the exposed surface of the self-assembled monolayer (SAM) adds significant diversity to this capability. Given the importance of carboxylic acid groups in applications ranging from controlling surface ionization to anchoring biological molecules, we have studied alternative ways to install acid groups on a surface and have probed the factors that control their chemistry.

Liquid phase deposition of a space-durable, antistatic SnO₂ coating on Kapton.

Polyimides are widely used in thermal blankets covering the external surfaces of spacecrafts due to their space durability and their thermo-optical properties. However, they are susceptible to atomic oxygen (AO) erosion, the main hazard of low Earth orbit (LEO), and to electrical charging. This work demonstrates that liquid phase deposition (LPD) of 100 nm of tin oxide creates a protective coating on Kapton polyimide that has good adherence and is effective in preventing AO-induced surface erosion and in reducing electrical charging.

Odd-even effect in molecular electronic transport via an aromatic ring.

A distinct odd-even effect on the electrical properties, induced by monolayers of alkyl-phenyl molecules directly bound to Si(111), is reported. Monomers of H2C═CH-(CH2)n-phenyl, with n = 2-5, were adsorbed onto Si-H and formed high-quality monolayers with a binding density of 50-60% Si(111) surface atoms. Molecular dynamics simulations suggest that the binding proximity is close enough to allow efficient π-π interactions and therefore distinctly different packing and ring orientations for monomers with odd or even numbers of methylenes in their alkyl spacers.

A nanometric cushion for enhancing scratch and wear resistance of hard films.

Scratch resistance and friction are core properties which define the tribological characteristics of materials. Attempts to optimize these quantities at solid surfaces are the subject of intense technological interest. The capability to modulate these surface properties while preserving both the bulk properties of the materials and a well-defined, constant chemical composition of the surface is particularly attractive.

Biofilm prevention on cochlear implants.

Objectives: To examine the efficiency of a bacteria-resistant coating for the polydimethylsiloxane (PDMS) casing of cochlear implants.

Methods: The coatings are based on thin titania films that are made by liquid phase deposition or atomic layer deposition. The antibacterial activity of the coating was tested by two different detection assays: BCA protein and confocal microscopy.

Monitoring the evaporation of fluids from fiber-optic micro-cell cavities.

Fiber-optic sensors provide remote access, are readily embedded within structures, and can operate in harsh environments. Nevertheless, fiber-optic sensing of liquids has been largely restricted to measurements of refractive index and absorption spectroscopy. The temporal dynamics of fluid evaporation have potential applications in monitoring the quality of water, identification of fuel dilutions, mobile point-of-care diagnostics, climatography and more.

Controlled formation of thiol and disulfide interfaces.

The work reported herein describes the controlled creation of uniform thiol-functionalized siloxane-anchored self-assembled monolayers (SAMs) and their selective transformation into intramonolayer (bridging) disulfides. These disulfides provide for the efficient immobilization of (bio)molecules bearing pendant thiols or disulfides, with no need for added oxidant. The unambiguous development of this surface chemistry required analytical methods that distinguish thiol and disulfide moieties on a surface.

Variations in the structure and reactivity of thioester functionalized self-assembled monolayers and their use for controlled surface modification.

Thioester-functionalized, siloxane-anchored, self-assembled monolayers provide a powerful tool for controlling the chemical and physical properties of surfaces. The thioester moiety is relatively stable to long-term storage and its structure can be systematically varied so as to provide a well-defined range of reactivity and wetting properties. The oxidation of thioesters with different-chain-length acyl groups allows for very hydrophobic surfaces to be transformed into very hydrophilic, sulfonic acid-bearing, surfaces.

Phosphonate-anchored monolayers for antibody binding to magnetic nanoparticles.

Targeted delivery of magnetic iron oxide nanoparticles (IONPs) to a specific tissue can be achieved by conjugation with particular biological ligands on an appropriately functionalized IONP surface. To take best advantage of the unique magnetic properties of IONPs and to maximize their blood half-life, thin, strongly bonded, functionalized coatings are required. The work reported herein demonstrates the successful application of phosphonate-anchored self-assembled monolayers (SAMs) as ultrathin coatings for such particles.

Sulfonation of alkyl phenyl ether self-assembled monolayers.

The sulfonation of phenyl ether decorated self-assembled monolayers (SAMs) was studied with an eye toward creating surfaces with a particularly high negative charge density based on a close-packed array of phenyl rings with more than one sulfonic acid group per molecule. The product distribution and kinetics of this process were studied by ultraviolet, infrared, and photoelectron spectroscopies and by monitoring changes in the thickness and wetting properties of the SAM. The sulfonation chemistry could be effected without undermining monolayer integrity and the isomer distribution of ortho- and para-monosulfonated material, along with the percentages of mono- and disulfonated molecules could be established throughout the process.

In situ sulfonation of alkyl benzene self-assembled monolayers: product distribution and kinetic analysis.

The sulfonation of aromatic rings held at the surface of a covalently anchored self-assembled monolayer has been analyzed in terms of the rates and isomer distribution of the sulfonation process. The observed product distributions are similar to those observed in solution, though the data obtained suggest that the reaction rate and the ortho/para product ratio depend on the length of the tether anchoring the aryl ring to the monolayer interface. It was also found that the interface becomes progressively more disordered and the observed reaction rates decrease as the reaction progresses.

Ozonolysis-based route to the in situ formation of aldehyde-bearing self-assembled monolayer surfaces.

While ozonolysis of a terminal carbon-carbon double bond to produce aldehydes is a well-established synthetic strategy for conventional solution chemistry, exposure of vinyl-terminated self-assembled monolayers to ozone has been reported to yield carboxylic acids. By using a cold solution of ozone in methanol and then adding a reducing agent to this solution, acid formation is minimized and near-quantitative aldehyde formation is achieved. The aldehyde-bearing surface is characterized by its physical and chemical properties and by ATR-FTIR spectroscopy showing a characteristic aldehyde C-H peak at 2715 cm(-1) and carbonyl peak at 1729 cm(-1).

Acid-base properties and zeta potentials of self-assembled monolayers obtained via in situ transformations.

Siloxane-anchored, self-assembled monolayers (SAMs) on single crystal Si were prepared with a variety of surface functional groups using a single commercially available surfactant (1-bromo-11-(trichlorosilyl)undecane) followed by in situ transformations. Polar (thioacetate and thiol), nonpolar (methyl), acidic (sulfonic and carboxylic), basic (various amines), and ionic (alkylammonium) surface functionalities were prepared. For primary amine and sulfonate surfaces, the degree of surface charge as a function of pH was determined ex situ using X-ray photoelectron spectroscopy (XPS).

In situ FTIR-ATR analysis and titration of carboxylic acid-terminated SAMs.

FTIR-ATR measurements permit detailed structural analysis and in situ titration of carboxylate-terminated self-assembled monolayers. Both monomeric and dimeric/oligomeric acid groups are seen, and their acid-base behavior is directly monitored. Monomers that are hydrogen bonded only to surrounding water molecules have a pKa = 4.

Molecular monolayer-mediated control over semiconductor surfaces: evidence for molecular depolarization of silane monolayers on Si/SiO(x).

We show that, for molecules with particularly strong dipoles, their organization into a monomolecular layer can lead to depolarization, something that limits the range over which the substrate's work function can be changed. It appears that, with molecules, depolarization is achieved by changes in orientation and conformation, rather than by charge transfer to the substrate as is common for atomic layers.