Silane-modified Glass Research Articles

Photothermal dual-responsive polymers for trypsin-free cell sheet harvesting

Cell sheet engineering has emerged to tackle cell therapy's bottlenecks and increase the likelihood of life-saving potentials of tissue engineering. In this study, Poly(N-isopropylacrylamide-co-spiropyran) (P(NIPAAm-co-Sp)) copolymer and Poly(N-isopropylacrylamide-co-styrene-co-spiropyran) (P(NIPAAm-co-St-co-Sp)) terpolymer were synthesized by free radical polymerization (FRP). Fourier transform infrared (FTIR) was utilized to characterize the chemical structure of the resultant polymers. The molecular weight and molecular weight distribution were measured by gel permeation chromatography (GPC). The reversible photosensitivity of the synthesized polymers was proved by ultraviolet–visible (UV–Vis) spectroscopy. Thin layers of polymers were spin-coated onto ultraviolet/ozone (UV-O3) and silane-modified glass slides. To confirm the coating process, the attenuated total reflection FTIR spectroscopy (ATR-FTIR) was used. The cross-sectional images of the spin-coated glass slides, obtained using field emission scanning electron microscopy (FESEM), showed thin layers about 300 to 400 nm thick. The roughness of the coated layers was examined by atomic force microscopy which were below 1 nm. The water contact angle (WCA) measurements showed that changes in the surface wettability of thin layers occurred in response to temperature alteration and light illumination. The spin-coated glass slides were used to culture the mouse fibroblast cell line L929. The cell culture results showed that the thickness of the thin layers was adequate for forming a confluent and integrated sheet of L929 cells. By reducing the temperature from 37 °C to 20 °C and illuminating the glass slide, fragments of the cell sheet were harvested. The use of light besides temperature reduction decreased the time needed for cell sheet detachment from 2 h to 1 h.

Tri-sodium citrate stabilized gold nanocubes for plasmonic glucose sensing

We report a two-step process for the immobilization of gold nanocubes (Au-NCs) on a glass surface using a combination of extraction and exchange reaction using poly (sodium 4-styrenesulfonate) (PSS) and trisodium citrate (TSC). Cetyltrimethylammonium chloride (CTAC) stabilized gold nanocubes (CTAC/Au-NCs) synthesized by a microfluidic synthesis procedure were successfully deposited on silane-modified glass substrate after extraction of excess CTAC using chloroform followed by exchange of CTAC to TSC on the surface of Au-NCs. Further, TSC/Au-NCs were found to be highly stable and suitable for microfluidic sensing of different glucose concentrations using localized surface plasmon resonance (LSPR) spectroscopy offering an improved sensitivity (126.37 nm/RIU).

Glass fiber reinforced PLA composite with enhanced mechanical properties, thermal behavior, and foaming ability

Polylatic acid (PLA) and PLA foams show a promising prospect for replacing the traditional petroleum-based polymers and foams. However, PLA shows poor ductility, thermal stability and foaming ability, and its application is significantly limited. Herein, silane-modified glass fibers (m-GF) were adopted to improve the mechanical properties, thermal stability, and foaming ability of PLA. PLA/m-GF composites with different GF contents were firstly prepared by twin-screw compounding. Microscopic morphology analysis showed that silane-modified GF has a good bonding with PLA matrix, and increasing GF content led to slight decreased of GF length. Mechanical testing showed that GF led to simultaneously enhanced strength, rigidness, and toughness. The higher the GF content is, the more obvious the reinforcement effect is. With 20 wt% GF, the PLA/m-GF composite shows almost 2-fold enhanced strength and rigidness, and more than 3-fold enhanced impact toughness than the pure PLA. The outstanding mechanical properties arises from the strengthening effect of the GF network skeleton that shows good bonding with PLA matrix. Thermal analysis showed that GF led to increased heat deflection temperature but reduced melt flow index of PLA. Foaming experiments showed that GF can dramatically improve the foaming ability by increasing expansion ratio and refining cellular morphology. Microcellular PLA/m-GF foam with an expansion ratio of up to 20-fold and cell sizes less than 10 μm was achieved. Thus, the strong PLA/m-GF composites and their foams show a promising future in preparing lightweight structural components used in many applications such as automotive and aircraft industries.

Strong and thermally insulating polylactic acid/glass fiber composite foam fabricated by supercritical carbon dioxide foaming

Environmental friendly and non-toxic polylactic acid (PLA) foam exhibits a promising perspective in many areas. However, PLA shows very poor foaming ability. Herein, silane-modified glass fiber (GF) was compounded with PLA to improve its foaming ability. Thanks to the increased melt viscoelasticity and melt strength, and the enhanced crystallization by adding GF, PLA/GF composites show dramatically improved foaming ability, characterized by widened processing window, increased expansion ratio, and improved cellular uniformity. Compared with pure PLA foam, PLA/GF composite foam shows dramatically enhanced mechanical properties in compressive strength and modulus. For foams with the same expansion ratio of 20-fold, the incorporation of 10 wt% GF led to increased compressive strength and modulus by 44.8% and 92.0%, respectively. The PLA/GF composite foam with an expansion ratio of 24.2-fold has a low thermal conductivity of 31.4 mW/m·K, which is comparable with the excellent thermal insulation performance of commercial polymer foams.

Defining the Properties of an Array of \u2013NH2-Modified Substrates for the Induction of a Mature Osteoblast/Osteocyte Phenotype from a Primary Human Osteoblast Population Using Controlled Nanotopography and Surface Chemistry

Accelerating the integration of a joint replacement or the healing of a bone fracture, particularly a complicated non-union fracture, would improve patient welfare and decrease healthcare costs. Currently, an autologous bone graft is the gold standard method for the treatment of complicated non-union fractures, but it is not always possible to harvest such a graft. A proactive highly inductive so-called smart material approach is pertinent in these cases. In this study, the surface chemistry of a previously approved material with desirable bulk material properties was modified to investigate its potential as an economical and effective alternative. The objective was to create stable synthetic chemical coatings that could guide cells along the osteogenic lineage required to generate mineralised tissue that would induce and accelerate bone healing. Primary human osteoblast-like cells were cultured in vitro for 7, 14 and 28 days on amine-terminated (chain length in the range 3–11) silane-modified glass surfaces with controlled nanotopography, to determine how surface chemistry and nanotopography change osteoblast function. The materials were characterised using atomic force microscopy (AFM), scanning electron microscopy (SEM), water contact angle (WCA) and a novel ninhydrin assay. The cells were analysed using qRT-PCR, von Kossa tinctural staining for mineralisation, and visualised using both transmitted white light and electron microscopy. Bone-like nodules, quantified using microscopy, only formed on the short-chain (chain length 3 and 4) amines after 7 days, as did the up-regulation of sclerostin, suggestive of a more mature osteoblast phenotype. In this paper, we report more rapid nodule formation than has previously been observed, without the addition of exogenous factors in the culture medium. This suggests that the coating would improve the integration of implants with bone or be the basis of a smart biomaterial that would accelerate the bone regeneration process.

Methacrylate Polymer Scaffolding Enhances the Stability of Suspended Lipid Bilayers for Ion Channel Recordings and Biosensor Development.

Black lipid membranes (BLMs) provide a synthetic environment that facilitates measurement of ion channel activity in diverse analytical platforms. The limited electrical, mechanical and temporal stabilities of BLMs pose a significant challenge to development of highly stable measurement platforms. Here, ethylene glycol dimethacrylate (EGDMA) and butyl methacrylate (BMA) were partitioned into BLMs and photopolymerized to create a cross-linked polymer scaffold in the bilayer lamella that dramatically improved BLM stability. The commercially available methacrylate monomers provide a simple, low cost, and broadly accessible approach for preparing highly stabilized BLMs useful for ion channel analytical platforms. When prepared on silane-modified glass microapertures, the resulting polymer scaffold-stabilized (PSS)-BLMs exhibited significantly improved lifetimes of 23 ± 9 to 40 ± 14 h and > 10-fold increase in mechanical stability, with breakdown potentials > 2000 mV attainable, depending on surface modification and polymer cross-link density. Additionally, the polymer scaffold exerted minimal perturbations to membrane electrical integrity as indicated by mean conductance measurements. When gramicidin A and α-hemolysin were reconstituted into PSS-BLMs, the ion channels retained function comparable to conventional BLMs. This approach is a key advance in the formation of stabilized BLMs and should be amenable to a wide range of receptor and ion channel functionalized platforms.

DNA-Based Patterning of Tethered Membrane Patches

Solid-supported lipid bilayers are useful model systems for mimicking cellular membranes; however, the interaction of the bilayer with the surface can disrupt the function of integral membrane proteins. As a result, many groups have introduced tethered lipid bilayers, which retain the proximity to the surface, enabling surface-sensitive techniques, but physically distance the bilayer from the surface. We have recently developed a method for spatially separating a lipid bilayer from a solid support using DNA lipids (Chung and Boxer et al., J. Struct. Biol., 2009). In this system, a DNA strand is covalently attached to a silane-modified glass slide or SiO2 wafer. The complementary DNA strand conjugated to a lipid moiety is inserted into giant unilamellar vesicles (GUVs), and the DNA-modified GUVs hybridize to the strands on the surface, inducing flattening and rupture of the GUV to a planar tethered lipid bilayer. However, the location of the patch is random, determined by where the DNA-GUV initially binds with its complement. To allow greater versatility and control, we sought a way to pattern tethered membrane patches. We present a method for creating spatially distinct tethered membrane patches on a glass slide using microarray printing. Surface-reactive DNA sequences are spotted onto the slide, incubated to covalently link the DNA to the surface, and DNA-GUVs patches are formed selectively on the printed DNA. Different DNA sequences can be printed on the same slide, creating a unique handle on each GUV patch. This handle enables the creation of patches of different lipid compositions, dyes, and/or DNA-lipid sequences in adjacent but distinct areas, and the control over the placement of the tethered lipid bilayer potentially allows interfacing with devices. This approach would also enable rapid screening of different patches in protein binding assays and as targets for membrane fusion.

Quantitative label-free characterization of avidin-biotin assemblies on silanized glass.

In this study, a time-of-flight secondary ion mass spectrometer TOF-SIMS, operating in the event-by-event bombardment/detection mode was used to characterize avidin-biotin assemblies on silane-modified glass substrates. SIMS was used to analyze several variants of the biointerface, including avidin physically adsorbed on a monofunctional acryl silane surface and covalently attached on monofunctional (amine terminated) and bifunctional (amine and acryl terminated) silanes. The goal of these studies was to determine density of avidin and biotin layers chemically or physically adsorbed on silanized glass substrate. An individual impact of a C(60) projectile used in this study creates a hemispherical crater (∼10 nm in diameter) and emits large numbers of secondary ions from the same nanovolume. Thus, a single impact enables one to unfold distinct secondary ions that span the thickness of the assembled film. This method was used to monitor the presence of glass, silane, and protein ions and to estimate the thickness and density of the avidin layer. In addition, we employed the double coincidence mass spectrometry approach to identify ions coemitted from a specific stratum of the biointerface. This approach was used to determine density of biotin and avidin immobilization while eliminating interferences from isobaric ions that originated from other constituents on the surface. Overall, novel TOF-SIMS quantitative approaches employed here were useful for examining complex biointerfaces and determining both lateral and in depth composition of the film.

Using growth factor arrays and micropatterned co-cultures to induce hepatic differentiation of embryonic stem cells

The success in driving embryonic stem cells towards hepatic lineage has been confounded by the complexity and cost of differentiation protocols that employ large quantities of expensive growth factors (GFs). Instead of supplementing culture media with soluble GFs, we investigated cultivation and differentiation of mouse embryonic stem cells (mESCs) on printed arrays of GFs. Hepatocyte growth factor (HGF), basic fibroblast growth factor (bFGF) and bone morphogenetic protein (BMP4) were mixed in solution with fibronectin and collagen (I) and then printed onto silane-modified glass slides to form 500 μm diameter protein spots. mESCs were cultured on top of GF spots for up to 12 days and analyzed by RT-PCR and immunostaining at different time points. The stem cells residing on HGF-containing combinations of GFs exhibited requisite features of hepatic differentiation including pronounced loss in pluripotency (Oct4), transient (up and down) expression of endoderm (Sox17) and upregulation of early hepatic markers – albumin and alpha-fetoprotein. The hepatic differentiation was enhanced further by adding hepatic stellate cells to surfaces that already contained mESCs on GF spots. A combination of co-culture with non-parenchymal liver cells and the optimal GF stimulation was found to induce endoderm and hepatic phenotype earlier and to a much greater extent than the GF arrays or micropatterned co-cultures used individually. While this paper investigated hepatic differentiation of mouse ESCs, our findings and stem cell culture approaches are likely to be relevant for human ESC cultivation. Overall, the platform combining printed GF arrays and heterotypic co-cultures will be broadly applicable for identifying the composition of the microenvironment niche for ESC differentiation into various tissue types.

Detecting cytokine release from single T-cells.

The cytokine production by leukocytes correlates with body's ability to mount an immune response and therefore has high diagnostic value. In the present study we employed microfabricated surfaces to capture T-cells from minimally processed human blood, arrange these cells into a single cell array, and then detect interferon (IFN)-gamma released from individual cells. The fabrication of cell capture surfaces started with coating a silane-modified glass slide with a uniform layer of poly(ethylene glycol) (PEG) hydrogel. The hydrogel-coated slide was lyophilized and then incubated with a mixture of monoclonal anti-IFN-gamma and anti-CD4 antibodies (Abs). To define sites for single cell attachment, PEG hydrogel microwells (20 microm diameter) were photolithographically patterned on top of the Ab-containing hydrogel layer. This micropatterning process resulted in fabrication of PEG hydrogel microwells with Ab-decorated bottom and nonfouling walls. To minimize the blood volume requirement and to precisely define shear stress conditions, the engineered surface was enclosed inside a PDMS-based microfluidic device. Introduction of red blood cell (RBC) depleted whole human blood followed by controlled washing led to the isolation of individual CD4 T-cells within PEG microwells. Mitogenic activation and immunofluorescent staining performed inside the microfluidic chamber revealed IFN-gamma cytokine signal colocalized with specific T-cells. The device and process presented here will be expanded in the future to enable multiparametric functional analysis of immune cells organized into high density single cell arrays.

Atomic force microscopy of the morphology and mechanical behaviour of barnacle cyprid footprint proteins at the nanoscale.

Barnacles are a major biofouler of man-made underwater structures. Prior to settlement, cypris larvae explore surfaces by reversible attachment effected by a 'temporary adhesive'. During this exploratory behaviour, cyprids deposit proteinaceous 'footprints' of a putatively adhesive material. In this study, footprints deposited by Balanus amphitrite cyprids were probed by atomic force microscopy (AFM) in artificial sea water (ASW) on silane-modified glass surfaces. AFM images obtained in air yielded better resolution than in ASW and revealed the fibrillar nature of the secretion, suggesting that the deposits were composed of single proteinaceous nanofibrils, or bundles of fibrils. The force curves generated in pull-off force experiments in sea water consisted of regions of gradually increasing force, separated by sharp drops in extension force manifesting a characteristic saw-tooth appearance. Following the relaxation of fibrils stretched to high strains, force-distance curves in reverse stretching experiments could be described by the entropic elasticity model of a polymer chain. When subjected to relaxation exceeding 500 ms, extended footprint proteins refolded, and again showed saw-tooth unfolding peaks in subsequent force cycles. Observed rupture and hysteresis behaviour were explained by the 'sacrificial bond' model. Longer durations of relaxation (>5 s) allowed more sacrificial bond reformation and contributed to enhanced energy dissipation (higher toughness). The persistence length for the protein chains (L(P)) was obtained. At high elongation, following repeated stretching up to increasing upper strain limits, footprint proteins detached at total stretched length of 10 microm.

Microfluidic-assisted analysis of replicating DNA molecules

Single molecule-based protocols have been gaining popularity as a way to visualize DNA replication at the global genomic- and locus-specific levels. These protocols take advantage of the ability of many organisms to incorporate nucleoside analogs during DNA replication, together with a method to display stretched DNA on glass for immunostaining and microscopy. We describe here a microfluidic platform that can be used to stretch and to capture labeled DNA molecules for replication analyses. This platform consists of parallel arrays of three-sided, 3- or 4-microm high, variable-width capillary channels fabricated from polydimethylsiloxane by conventional soft lithography, and of silane-modified glass coverslips to reversibly seal the open side of the channels. Capillary tension in these microchannels facilitates DNA loading, stretching and glass coverslip deposition from microliter-scale DNA samples. The simplicity and extensibility of this platform should facilitate DNA replication analyses using small samples from a variety of biological and clinical sources.

Cultivating liver cells on printed arrays of hepatocyte growth factor

Growth factors are commonly present in soluble form during in vitro cell cultivation experiments in order to provide signals for cellular proliferation or differentiation. In contrast to these traditional experiments, we investigated solid-phase presentation of a hepatocyte growth factor (HGF), a protein important in liver development and regeneration, on microarrays of extracellular matrix (ECM) proteins. In our experiments, HGF was mixed in solution with ECM proteins (collagen (I), (IV) or laminin) and robotically printed onto silane-modified glass slides. Primary rat hepatocytes were seeded onto HGF/ECM protein microarrays and formed cellular clusters that corresponded in size to the dimensions of individual protein spots (500 μm diameter). Analysis of liver-specific products, albumin and α1-antitrypsin, revealed several fold higher levels of expression of these proteins in hepatocytes cultured on HGF/ECM microarrays compared to cells cultivated on ECM proteins alone. In addition, cultivation of hepatocytes on HGF/ECM protein spots led to spontaneous reorganization of cellular clusters from a monolayer into three-dimensional spheroids. We also investigated the effects of surface-tethered HGF on hepatocytes co-cultivated with stromal cells and observed a significantly higher level of albumin in co-cultures where hepatocytes were stimulated by HGF/ECM spots compared to co-cultures created on ECM protein islands without the growth factor. In summary, our study suggests that incorporation of HGF into ECM protein microarrays has a profound and long-lasting effect on the morphology and phenotype of primary hepatocytes. In the future, the number of growth factors printed on ECM microarrays will be expanded to enable multiplexed and combinatorial screening of inducers of cellular differentiation or proliferation.

Integrating Sensing Hydrogel Microstructures into Micropatterned Hepatocellular Cocultures

In this paper we describe a microfabrication-derived approach for defining interactions between distinct groups of cells and integrating biosensors with cellular micropatterns. In this approach, photoresist lithography was employed to micropattern cell-adhesive ligand (collagen I) on silane-modified glass substrates. Poly(ethylene glycol) (PEG) photolithography was then used to fabricate hydrogel microstructures in registration with existing collagen I domains. A glass substrate modified in this manner had three types of micropatterned regions: cell-adhesive collagen I domains, moderately adhesive silanized glass regions, and nonadhesive PEG hydrogel regions. Incubation of this substrate with primary rat hepatocytes or HepG2 cells resulted in attachment of hepatic cells on collagen I domains with no adhesion observed on silane-modified glass regions or hydrogel domains. 3T3 fibroblasts added onto the same surface attached on the glass regions around the hepatocytes, completing the coculture. Significantly, PEG hydrogel microstructures remained free of cells and were used to "fence" hepatocytes from fibroblasts, thus limiting communication between the cell types. We also demonstrated that entrapment of enzyme molecules inside hydrogel microstructures did not compromise nonfouling properties of PEG. Building on this result, horse radish peroxidase-containing hydrogel microstructures were integrated into micropatterned cocultures and were used to detect hydrogen peroxide in the culture medium. The surface micropatterning approach described here may be used in the future to simultaneously define and detect endocrine signaling between two distinct cell types.

Single-molecule immunosorbent assay as a tool for human immunodeficiency virus-1 antigen detection

Ultrasensitive detection and quantification of viral antigen with a novel single-molecule immunosorbent assay (SMISA) was achieved. Antigen from human immunodeficiency virus type 1 (HIV-1), the major etiological agent of acquired immune deficiency syndrome, served as the screening target in this study. The target molecule was sandwiched between a polyclonal capture antibody and a monoclonal detector antibody. The capture antibody was covalently immobilized on (3-glycidoxypropyl) trimethoxy silane-modified glass slides. The detector antibody was conjugated with fluorescent Alexa Fluor 532 labeled secondary antibody prior to being used as a probe for the antigen. Imaging was performed with a total internal reflection fluorescence single-molecule detection system. This technique is demonstrated for detecting HIV-1 p24 antigen down to 0.1 pg/mL with a dynamic range of over four orders of magnitude. A Langmuir isotherm fits the molecule count dependence on the target concentration. The target antigen was further tested in 20% human serum, and the results showed that neither sensitivity nor dynamic range was affected by the biological matrix. SMISA is therefore a promising approach for the early diagnosis of viral induced diseases.

Analysis of Local Tissue-Specific Gene Expression in Cellular Micropatterns

While cellular micropatterning approaches are employed extensively in cell biology and tissue engineering, only a limited number of methods for analysis of local function in the context of a complex, microfabricated environment are currently available. The present study develops a novel strategy for analysis of local tissue-specific function in cellular micropatterns. Model hepatocytes (HepG2 cells) were seeded onto silane-modified glass slides containing robotically printed arrays of collagen type I. These model hepatocytes formed cell arrays with individual cell cluster dimensions (150 or 500 microm) corresponding in size to the printed collagen spots. Non-parenchymal cells (3T3 fibroblasts) were added to hepatocellular micropatterns to create heterotypic cocultures. Expression of hepatic phenotype in HepG2 cells was first verified by traditional techniques including intracellular staining and ELISA for albumin. In order to evaluate local liver function in the cellular microarray, individual array members composed of approximately 400 hepatocytes were retrieved using laser capture microdissection and analyzed with real-time reverse transcriptase (RT)-polymerase chain reaction (PCR). Hepatic function was assessed based on expression of four genes associated with differentiated liver phenotype: albumin, transferrin, alpha-fetoprotein, and alpha1-antitrypsin. "Titration" experiments, carried out to identify the smallest population of HepG2 cells yielding detectable mRNA levels and RT-PCR signals, showed that extraction area of 12,500 microm2 (corresponding to approximately 70 cells) provided detectable gene expression signals. All four liver-specific genes were routinely evaluated after extraction of approximately 400 HepG2 from the micropatterned surfaces. Significantly, selective retrieval and subsequent analysis of tissue-specific function was demonstrated for hepatic cells micropatterned alone and in coculture with non-parenchymal cells. In the future, methods described in this study will offer the possibility to investigate dynamic and reciprocal interactions between two or more cell types positioned on a microfabricated cell culture surface. We also envision the proposed approaches to be ideally suited for cell analysis in the context of combinatorial microenvironment.

Bioresponsive Hydrogel Microlenses

We report investigations of bioresponsive hydrogel microlenses as a new protein detection technology. Stimuli-responsive poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc) microgels have been synthesized via free-radical precipitation polymerization. These hydrogel microparticles were then functionalized with biotin via EDC coupling. Hydrogel microlenses were prepared from the particles via Coulombic assembly onto a silane-modified glass substrate. Arrays containing both pNIPAm-co-AAc microgels (as an internal control) and biotinylated pNIPAm-co-AAc microgels were then used to detect multivalent binding of both avidin and polyclonal anti-biotin. Protein binding was determined by monitoring the optical properties of the microlenses using a brightfield optical microscopy technique. The microlens method is shown to be very specific for the target protein, with no detectable interference from nonspecific protein binding. Finally, the reversibility of the hydrogel microlens assay has been studied in the case of anti-biotin to determine the potential application of the microlens assay technology in a displacement-type assay. These results suggest that the microlens method may be an appropriate one for label-free detection of proteins or small molecules via displacement of tethered protein--ligand pairs.

Controlling modulus and morphology of hydrogel tubes through surface modification

Crosslinked, porous poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) tubes were prepared in cylindrical glass molds using a new centrifugal casting process developed in our group. The resulting hydrogel tubes have a bi-phasic wall structure, with a spongy inner layer and a gel-like outer layer, the latter of which provides mechanical strength to the tube. While many factors influence wall morphology and, thus, mechanical properties, we focused on the effect of the surface properties of the glass mold in which tubes are synthesized. Specifically, we investigated the impact of a diverse set of silane modifications of the glass mold on tube morphology, elastic modulus and mold release. We treated activated glass surfaces with one of three alkoxysilanes having either ethoxy, amine or fluorocarbon end-groups. Silane-modified glass surfaces were found to be more hydrophobic than the unmodified glass mold, with the most hydrophobic surface being that of the fluorocarbon-terminated silane. The presence of the silane layer on the mold was confirmed by X-ray photoelectron spectroscopy and the stability of this modification was confirmed by examining the surface chemistry of the hydrogel tubes. The biphasic hydrogel tube wall structure was observed for all tubes, yet those tubes synthesized in unmodified molds had a cracked outer morphology, whereas those synthesized in silane-modified molds had a smooth outer morphology. This influenced the mechanical properties of the tubes where tubes synthesized in silane-modified molds had a significantly greater elastic modulus than those tubes synthesized in unmodified molds. Release from the molds was easiest with ethoxy- and amine-functionalized silane mold modifications.

Angular evaluation to quantify planar distortions of PDMS stamps in soft lithography

This article describes an angular quantification method of planar distortion for polydimethylsiloxane (PDMS) stamps in soft lithography by introducing angular parameter θ that is proportional to patterns’ planar distortion in magnitude. The average planar distortion of individual pattern (absolute distortion, θ 1) and pattern-to-pattern distortion (relative distortion, θ 2) of PDMS stamps were determined by angular discrepancies ( θ). The angular quantification was evaluated among four different PDMS stamps affixation treatments, and the PDMS stamps supported on silane-modified glass showed strong binding and minimal planar distortion. Its absolute angular distortion θ 1 was 3.98×10 −3 and relative angular distortion θ 2 was 1.22×10 −3. The angular evaluations demonstrate a versatile method for quantifying and comparing planar distortions among patterns as well as screening elastomer stamps support in soft lithography.

Characteristics of nanoscopic Au band electrodes

Gold band electrodes with widths ranging from 3 to 150 nm are used to investigate the voltammetric response of a series of substituted ferrocenes in non-aqueous electrolyte. The Au electrodes are fabricated by insulating, with an epoxy, all but the edge of an evaporated Au film deposited onto a silane-modified glass substrate. Plots of normalized limiting current for each ferrocene derivative as a function of normalized electrode width reveal a negative response from traditional theoretical predictions. The theory used for the band electrodes is based on semiinfinite diffusion of the ferrocenes to a hemicylindrical electrode. The observed negative responses for electrodes less than 50 nm in width are explained by effects that become important when the sizes of the electrode and redox species are comparable. Concerns regarding the real surface area of the band electrodes are addressed by labeling of the exposed Au of the nanoband electrode with a ferrocene-tagged alkanethiol and measurements of double-layer capacitance. These studies indicate that roughly 20–500 times more area is exposed than that calculated from the nominal width and length of the bands, even though X-ray diffraction and stylus profilometry determinations of Au thickness are in agreement with those found by quartz crystal microgravimetry during evaporation of the Au films. Scanning electron microscopy studies of the epoxy ∣ Au ∣ glass interface point to insufficient insulation of the Au by the epoxy as the result of defects.