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Biomedical subjects

Ralph G Nuzzo

Publications and source records attributed to Ralph G Nuzzo.

At least 19 recordsLinked to original sources
PubMed2006

Heterogeneous three-dimensional electronics by use of printed semiconductor nanomaterials.

We developed a simple approach to combine broad classes of dissimilar materials into heterogeneously integrated electronic systems with two- or three-dimensional layouts. The process begins with the synthesis of different semiconductor nanomaterials, such as single-walled carbon nanotubes and single-crystal micro- and nanoscale wires and ribbons of gallium nitride, silicon, and gallium arsenide on separate substrates. Repeated application of an additive, transfer printing process that uses soft stamps with these substrates as donors, followed by device and interconnect formation, yields high-performance heterogeneously integrated electronics that incorporate any combination of semiconductor nanomaterials on rigid or flexible device substrates. This versatile methodology can produce a wide range of unusual electronic systems that would be impossible to achieve with other techniques.

Journal Article↗
PubMed2006

Quantitative multispectral biosensing and 1D imaging using quasi-3D plasmonic crystals.

We developed a class of quasi-3D plasmonic crystal that consists of multilayered, regular arrays of subwavelength metal nanostructures. The complex, highly sensitive structure of the optical transmission spectra of these crystals makes them especially well suited for sensing applications. Coupled with quantitative electrodynamics modeling of their optical response, they enable full multiwavelength spectroscopic detection of molecular binding events with sensitivities that correspond to small fractions of a monolayer. The high degree of spatial uniformity of the crystals, formed by a soft nanoimprint technique, provides the ability to image binding events over large areas with micrometer spatial resolution. These features, together with compact form factors, low-cost fabrication procedures, simple readout apparatus, and ability for direct integration into microfluidic networks and arrays, suggest promise for these devices in label-free bioanalytical detection systems.

Avidin↗
PubMed2006

Unusual non-bulk properties in nanoscale materials: thermal metal-metal bond contraction of gamma-alumina-supported Pt catalysts.

Variable-temperature X-ray absorption spectroscopy measurements of sub-nanometer Pt nanoparticles on a high-surface-area gamma-alumina support reveal that the Pt-Pt bonds exhibit contraction upon heating [i.e., negative thermal expansion (NTE)]. Bare clusters under a He environment show an average linear expansion coefficient of -2.5 x 10-5 K-1 over the temperature range studied. Adsorption of hydrogen results in an overall bond relaxation and less dramatic Pt-Pt thermal bond-length contraction. From the temperature effect on bond length, disorder parameters, and the X-ray absorption near edge structure (XANES) spectra, temperature-dependent charge transfer between the support and the Pt clusters was concluded to be responsible for the observed behavior.

Journal Article↗
PubMed2006

Effects of temperature on the alignment and electrooptical responses of a nematic nanoscale liquid crystalline film.

The surface-induced alignment and electrooptical (EO) dynamics of a 50-nm-thick liquid crystalline (4-n-pentyl-4'-cyanobiphenyl; 5CB) film were studied at three temperatures: 25 and 33 degrees C (near the crystalline-nematic and nematic-isotropic transition temperatures, respectively) and 29 degrees C (a median temperature in the stability region of the nematic phase). The ZnSe surfaces that entrap the liquid crystal (LC) film have been polished unidirectionally to produce a grooved surface presenting nanometer-scale corrugations, a structure that induces a planar and homogeneous orientation in the nematic phase. The present work attempts to understand the influences of temperature on the surface-induced alignment and corresponding EO dynamics of the material. Step-scan time-resolved spectroscopy measurements were made to determine the rate constants for the electric-field-induced orientation and thermal relaxation of the 5CB film. The field-driven orientation rates vary sensitively with temperature across a range that spans the stability limits of the nematic phase; the relaxation rates, however, vary very little across this same temperature range. We propose that these differences in LC behavior arise as consequence of the interplay of the temperature dependence of the elastic constants, viscosity, and degree of orientational order of the LC medium. A simple theoretical model provides some understanding of these behaviors.

Biphenyl Compounds↗
PubMed2006

Metal core bonding motifs of monodisperse icosahedral Au13 and larger Au monolayer-protected clusters as revealed by X-ray absorption spectroscopy and transmission electron microscopy.

The atomic metal core structures of the subnanometer clusters Au13[PPh3]4[S(CH2)11CH3]2Cl2 (1) and Au13[PPh3]4[S(CH2)11CH3]4 (2) were characterized using advanced methods of electron microscopy and X-ray absorption spectroscopy. The number of gold atoms in the cores of these two clusters was determined quantitatively using high-angle annular dark field scanning transmission electron microscopy. Multiple-scattering-path analyses of extended X-ray absorption fine structure (EXAFS) spectra suggest that the Au metal cores of each of these complexes adopt an icosahedral structure with a relaxation of the icosahedral strain. Data from microscopy and spectroscopy studies extended to larger thiolate-protected gold clusters showing a broader distribution in nanoparticle core sizes (183 +/- 116 Au atoms) reveal a bulklike fcc structure. These results further support a model for the monolayer-protected clusters (MPCs) in which the thiolate ligands bond preferentially at 3-fold atomic sites on the nanoparticle surface, establishing an average composition for the MPC of Au180[S(CH2)11CH3]40. Results from EXAFS measurements of a gold(I) dodecanethiolate polymer are presented that offer an alternative explanation for observations in previous reports that were interpreted as indicating Au MPC structures consisting of a Au core, Au2S shell, and thiolate monolayer.

Journal Article↗
PubMed2006

Anchoring and electro-optical dynamics of thin liquid crystalline films in a polyimide cell: experiment and theory.

The surface-dependent anchoring and electro-optical (EO) dynamics of thin liquid crystalline films have been examined using Fourier transform infrared spectroscopy. A simple nematic liquid crystal, 4-n-pentyl-4'-cyanobiphenyl (5CB), is confined as 40, 50, and 390 nm thick films in nanocavities defined by gold interdigitated electrode arrays (IDEAs) patterned on polyimide-coated zinc selenide (ZnSe) substrates [Noble et al., J. Am. Chem. Soc. 124, 15020 (2002)]. New strategies for controlling the anchoring interactions and EO dynamics are explored based on coating a ZnSe surface with an organic polyimide layer in order to both planarize the substrate and induce a planar alignment of the liquid crystalline film. The polyimide layer can be further treated so as to induce a strong alignment of the nematic director along a direction parallel to the electrode digits of the IDEA. Step-scan time-resolved spectroscopy measurements were made to determine the rate constants for the electric-field-induced orientation and thermal relaxation of the 5CB films. In an alternate set of experiments, uncoated ZnSe substrates were polished unidirectionally to produce a grooved surface presenting nanometer-scale corrugations. The dynamical rate constants measured for several nanoscale film thicknesses and equilibrium organizations of the director in these planar alignments show marked sensitivities. The orientation rates are found to vary strongly with both the magnitude of the applied potential and the initial anisotropy of the alignment of the director within the IDEA. The relaxation rates do not vary in this same way. The marked variations seen in EO dynamics can be accounted for by a simple coarse-grained dynamical model.

Journal Article↗
PubMed2006

Sub-nanometer Au monolayer-protected clusters exhibiting molecule-like electronic behavior: quantitative high-angle annular dark-field scanning transmission electron microscopy and electrochemical characterization of clusters with precise atomic stoichiometry.

The synthesis and characterization of the clusters Au13[PPh3]4[S(CH2)11CH3]2Cl2 (1) and Au13[PPh3]4[S(CH2)11CH3]4 (2) are described. These mixed-ligand, sub-nanometer clusters, prepared via exchange of dodecanethiol onto phosphine-halide gold clusters, show enhanced stability relative to the parent. The characterization of these clusters features the precise determination of the number of gold atoms in the cluster cores using high-angle annular dark-field scanning transmission electron microscopy, allowing the assignment of 13 gold atoms (+/-3 atoms) to the composition of both cluster molecules. Electrochemical and optical measurements reveal discrete molecular orbital levels and apparent energy gaps of 1.6-1.7 eV for the two cluster molecules. The electrochemical measurements further indicate that the Au13[PPh3]4[S(CH2)11CH3]2Cl2 cluster undergoes an overall two-electron reduction. The electrochemical and spectroscopic properties of the two Au13 cluster molecules are compared with those of a secondary synthetic product, which proved to be larger Au thiolate-derivatized monolayer-protected clusters with an average core of Au180. The latter shows behavior fully consistent with the adoption of metallic-like properties.

Journal Article↗
PubMed2006

Quantitative imaging of protein adsorption on patterned organic thin-film arrays using secondary electron emission.

Secondary electron emission is developed as a means to quantify and image protein binding to Au surfaces modified with patterned organic thin-film arrays. Alkane thiols were patterned via microcontact printing on gold, and their effects on the secondary electron (SE) yield of the surface, systematically quantified. We show that a self-assembled monolayer (SAM) of hexadecane thiol significantly increases the SE yield over the native gold surface, a yield that increases as a function of alkane chain length (C8-C16). This effect is linearly correlated with the surface potentials and wetting properties of these SAMs. Surface layers comprised of poly(ethylene glycol) (PEG) grafted polyacrylamide polymers behave differently, affecting the SE yield by attenuation according to the polymer thickness. These results demonstrate the relative contributions of factors related to the adsorbate molecular structures that serve to strongly mediate the SE yield, providing a foundation for exploiting them as a quantitative electron imaging probe. The latter capability is demonstrated using a model microfluidic assay in which a series of proteins was spatially addressed to a SAM-based pixel array. The gray scale contrasts seen with protein adsorption are directly correlated with both protein molecular weight and mass coverage. These methods are used in two model protein assay experiments: (1) the measurement of the concentration dependent adsorption isotherm for a model protein (fibrinogen); and (2) the selective recognition of a biotinylated protein layer by avidin. These results demonstrate a unique approach to imaging protein binding processes on surfaces with both high analytical and spatial sensitivity.

Acrylic Resins↗
PubMed2006

A passive microfluidic hydrogen-air fuel cell with exceptional stability and high performance.

We describe an advanced microfluidic hydrogen-air fuel cell (FC) that exhibits exceptional durability and high performance, most notably yielding stable output power (>100 days) without the use of an anode-cathode separator membrane. This FC embraces an entirely passive device architecture and, unlike conventional microfluidic designs that exploit laminar hydrodynamics, no external pumps are used to sustain or localize the reagent flow fields. The devices incorporate high surface area/porous metal and metal alloy electrodes that are embedded and fully immersed in liquid electrolyte confined in the channels of a poly(dimethylsiloxane) (PDMS)-based microfluidic network. The polymeric network also serves as a self-supporting membrane through which oxygen and hydrogen are supplied to the cathode and alloy anode, respectively, by permeation. The operational stability of the device and its performance is strongly dependent on the nature of the electrolyte used (5 M H2SO4 or 2.5 M NaOH) and composition of the anode material. The latter choice is optimized to decrease the sensitivity of the system to oxygen cross-over while still maintaining high activity towards the hydrogen oxidation reaction (HOR). Three types of high surface area anodes were tested in this work. These include: high-surface area electrodeposited Pt (Pt); high-surface area electrodeposited Pd (Pd); and thin palladium adlayers supported on a "porous" Pt electrode (Pd/Pt). The FCs display their best performance in 5 M H2SO4 using the Pd/Pt anode. This exceptional stability and performance was ascribed to several factors, namely: the high permeabilities of O2, H2, and CO2 in PDMS; the inhibition of the formation of insoluble carbonate species due to the presence of a highly acidic electrolyte; and the selectivity of the Pd/Pt anode toward the HOR. The stability of the device for long-term operation was modeled using a stack of three FCs as a power supply for a portable display that otherwise uses a 3 V battery.

Air↗
PubMed2006

Origin of bulklike structure and bond length disorder of Pt37 and Pt6Ru31 clusters on carbon: comparison of theory and experiment.

We describe a theoretical analysis of the structures of self-organizing nanoparticles formed by Pt and Ru-Pt on carbon support. The calculations provide insights into the nature of these metal particle systems-ones of current interest for use as the electrocatalytic materials of direct oxidation fuel cells-and clarify complex behaviors noted in earlier experimental studies. With clusters deposited via metallo-organic Pt or PtRu(5) complexes, previous experiments [Nashner et al. J. Am. Chem. Soc. 1997, 119, 7760; Nashner et al. J. Am. Chem. Soc. 1998, 120, 8093; Frenkel et al. J. Phys. Chem. B 2001, 105, 12689] showed that the Pt and Pt-Ru based clusters are formed with fcc(111)-stacked cuboctahedral geometry and essentially bulklike metal-metal bond lengths, even for the smallest (few atom) nanoparticles for which the average coordination number is much smaller than that in the bulk, and that Pt in bimetallic [PtRu(5)] clusters segregates to the ambient surface of the supported nanoparticles. We explain these observations and characterize the cluster structures and bond length distributions using density functional theory calculations with graphite as a model for the support. The present study reveals the origin of the observed metal-metal bond length disorder, distinctively different for each system, and demonstrates the profound consequences that result from the cluster/carbon-support interactions and their key role in the structure and electronic properties of supported metallic nanoparticles.

Journal Article↗
PubMed2005

Masterless soft lithography: patterning UV/ozone-induced adhesion on poly(dimethylsiloxane) surfaces.

A novel microreactor-based photomask capable of effecting high resolution, large area patterning of UV/ozone (UVO) treatments of poly(dimethylsiloxane) (PDMS) surfaces is described. This tool forms the basis of two new soft lithographic patterning techniques that significantly extend the design rules of decal transfer lithography (DTL). The first technique, photodefined cohesive mechanical failure, fuses the design rules of photolithography with the contact-based adhesive transfer of PDMS in DTL. In a second powerful variation, the UVO masks described in this work enable a masterless soft lithographic patterning process. This latter method, UVO-patterned adhesive transfer, allows the direct transfer of PDMS-based polymer microstructures from a slab of polymer to silicon and other material surfaces. Both methods exploit the improved process qualities that result from the use of a deuterium discharge lamp to affect the UVO treatment to pattern complex, large area PDMS patterns with limiting feature sizes extending well below 1 microm (> or = 0.3 microm). The use of these structures as resists is demonstrated for the patterning of metal thin films. A time-of-flight secondary ion mass spectroscopy study of the process provides new insights into the mechanisms that contribute to the chemistry responsible for the interfacial adhesion of DTL transfers.

Journal Article↗
PubMed2005

An electrochemically driven poly(dimethylsiloxane) microfluidic actuator: oxygen sensing and programmable flows and pH gradients.

We describe the fabrication and performance of an integrated microelectrochemical reactor-a design possessing utility for multiple applications that include electrochemical sensing, the generation and manipulation of in-channel microfluidic pH gradients, and fluid actuation and flow. The device architecture is based on a three-electrode electrochemical cell design that incorporates a Pt interdigitated array (IDA) working (WE), a Pt counter (CE), and Ag pseudo-reference (RE) electrodes within a microfluidic network in which the WE is fully immersed in a liquid electrolyte confined in the channels. The microchannels are made from a conventional poly(dimethylsiloxane)(PDMS) elastomer, which serves also as a thin gas-permeable membrane through which gaseous reactants in the external ambient environment are supplied to the working electrode by diffusion. Due to the high permeability of oxygen through PDMS, the microfluidic cell supports significantly (>order of magnitude) higher current densities in the oxygen reduction reaction (ORR) than those measured in conventional (quiescent) electrochemical cells for the same electrode areas. We demonstrate in this work that, when operated at constant potential under mass transport control, the device can be utilized as a membrane-covered oxygen sensor, the response of which can be tuned by varying the thickness of the PDMS membrane. Depending on the experimental conditions under which the electrochemical ORR is performed, the data establish that the device can be operated as both a programmable pH gradient generator and a microfluidic pump.

Diffusion↗
PubMed2005

Near-IR luminescence of monolayer-protected metal clusters.

Visible-near-IR luminescence spectra of gold MPCs that are similar, irrespective of the number of core atoms (all <2 nm diameter) and different monolayers, are reported. The luminescence can be quantitatively invoked by introducing polar ligands into nonpolar MPC monolayers and by galvanic exchange of metal atoms on the MPC core surface with different metals. The observed emissions are believed to result from surface-localized states that depend on both the core metal of the nanoparticle and the ligands attached to the metal surface.

Journal Article↗
PubMed2005

Large-area patterning of coinage-metal thin films using decal transfer lithography.

We describe two new procedures that appear to hold significant promise as means for patterning thin-film microstructures of the coinage metals (Cu, Ag, Au). A feature central to both is the modification of their surfaces to promote the adhesive transfer of PDMS thin-film microstructures, a material suitable for use as resist layers in large-area patterning, using Decal Transfer Lithography (DTL). The present work provides a significant extension of the capabilities of DTL patterning, providing general protocols that can be used to transfer decal resists to essentially any substrate surface. The first method involves the functionalization of a surface, specifically those of gold and silver films with a thiol-terminated silane coupling agent, (mercaptopropyl)trimethoxysilane. This self-assembled monolayer, when hydrolyzed to its silanol form, provides a robust adhesion-promoting layer suitable for use in DTL patterning. The second method exploits the surface chemistry provided by the deposition of a nanoscale silicon dioxide thin-film capping layer using e-beam evaporation. This procedure provides an exceptional method for patterning large-area, thin-film microstructures of Cu-one compatible with micrometer-scale design rules-that are essentially defect free. Both surface modification strategies enable high-quality poly(dimethylsiloxane) decal transfers, and as the current work shows, these structures are suitable for large-area micrometer-sized patterning of gold, silver, and copper thin films via both wet-etching and lift-off procedures.

Journal Article↗
PubMed2005

Additive soft-lithographic patterning of submicrometer- and nanometer-scale large-area resists on electronic materials.

We describe a novel soft-lithographic technique possessing broad utility for the fabrication of large area, nanoscale ( approximately 100 nm) multilayer resist structures on electronic material substrates. This additive patterning method transfers ultrathin poly(dimethylsiloxane) (PDMS) decals to an underlying SiO(2)-capped organic planarazation layer. The PDMS patterns serve as a latent image through which high-quality multilayer resist structures can be developed using reactive ion-beam etching.

Crystallization↗
PubMed2004

Growth kinetics and morphology of self-assembled monolayers formed by contact printing 7-octenyltrichlorosilane and octadecyltrichlorosilane on Si(100) wafers.

The growth kinetics and morphologies of self-assembled monolayers deposited by contact printing 7-octenyltrichlorosilane (OCT) and octadecyltrichlorosilane (OTS) on Si(100) were studied by ellipsometry and atomic force microscopy. We found that, for both OCT and OTS, full monolayers could be obtained at room temperature after printing times of 120-180 s; the printing-based monolayer assembly processes follow apparent Langmuir adsorption kinetics, with the measured film growth rates increasing both with the ambient humidity and with concentration of the ink used to load the stamp. At a dew point of 10 degrees C and an ink concentration (in toluene) of 50 mM, the observed film growth rate constant is 0.05 s(-)(1). When the printing was carried out at a lower ambient humidity (dew points of 1-3 degrees C), the measured rates of assembly were approximately a factor of 2 slower. Increasing the deposition temperature from 25 to 45 degrees C under these conditions increased the film growth rate only slightly. The morphology of the films depends on the identity of the ink. Uniform, high-coverage films could be obtained readily from the eight-carbon chain length adsorbate OCT, provided that the stamp was not overloaded with the ink; for high concentrations outside of the optimal range, the surface presented significant numbers of adsorbed particles ascribed, in part, to siloxane polymers formed by hydrolysis of the ink on the stamp before printing. In marked contrast, for the 18-carbon adsorbate OTS, the printed films always consisted of a mixture of a uniform monolayer plus adsorbed polysiloxane particles. The different film morphologies seen for OCT and OTS are proposed to result from the different transfer efficiencies of the organotrichlorosilane relative to polysiloxane hydrolysis products formed during the printing process. These transfer efficiencies exhibit sensitivities related to the permeation of the poly(dimethylsiloxane) (PDMS) stamp by the silane reagents. Short-chain inks such as OCT evidently permeate the PDMS stamp more deeply than longer-chain inks such as OTS. This difference, and the different diffusion rates of ink vs oligomeric silane hydrolysis products, determines the film morphology obtained by contact printing. The mass transfer dynamics of the process thus yield surface layers derived from varying quantities of siloxane oligomers, which subsequently transfer to the substrate along with unhydrolyzed silane adsorbate during the printing step. The structural evolution of the contact-printed films so obtained is strikingly different from that of SAMs prepared by immersion.

Adsorption↗