Open Access. Powered by Scholars. Published by Universities.®

Biomedical Engineering and Bioengineering Commons

Open Access. Powered by Scholars. Published by Universities.®

Chemical Engineering

Andrew C. Hillier

Articles 1 - 15 of 15

Full-Text Articles in Biomedical Engineering and Bioengineering

Epitaxially Grown Collagen Fibrils Reveal Diversity In Contact Guidance Behavior Among Cancer Cells, Juan Wang, Joseph W. Petefish, Andrew C. Hillier, Ian C. Schneider May 2017

Epitaxially Grown Collagen Fibrils Reveal Diversity In Contact Guidance Behavior Among Cancer Cells, Juan Wang, Joseph W. Petefish, Andrew C. Hillier, Ian C. Schneider

Andrew C. Hillier

Invasion of cancer cells into the surrounding tissue is an important step during cancer progression and is driven by cell migration. Cell migration can be random, but often it is directed by various cues such as aligned fibers composed of extracellular matrix (ECM), a process called contact guidance. During contact guidance, aligned fibers bias migration along the long axis of the fibers. These aligned fibers of ECM are commonly composed of type I collagen, an abundant structural protein around tumors. In this paper, we epitaxially grew several different patterns of organized type I collagen on mica and compared the morphology ...


Angle-Tunable Enhanced Infrared Reflection Absorption Spectroscopy Via Grating-Coupled Surface Plasmon Resonance, Joseph W. Petefish, Andrew C. Hillier Jun 2014

Angle-Tunable Enhanced Infrared Reflection Absorption Spectroscopy Via Grating-Coupled Surface Plasmon Resonance, Joseph W. Petefish, Andrew C. Hillier

Andrew C. Hillier

Surface enhanced infrared absorption (SEIRA) spectroscopy is an attractive method for increasing the prominence of vibrational modes in infrared spectroscopy. To date, the majority of reports associated with SEIRA utilize localized surface plasmon resonance from metal nanoparticles to enhance electromagnetic fields in the region of analytes. Limited work has been performed using propagating surface plasmons as a method for SEIRA excitation. In this report, we demonstrate angle-tunable enhancement of vibrational stretching modes associated with a thin poly(methyl methacrylate) (PMMA) film that is coupled to a silver-coated diffraction grating. Gratings are fabricated using laser interference lithography to achieve precise surface ...


Electrochemically Modulated Permeability Of Poly(Aniline) And Composite Poly(Aniline)−Poly(Styrenesulfonate) Membranes, D. L. Pile, Y. Zhang, Andrew C. Hillier Jun 2014

Electrochemically Modulated Permeability Of Poly(Aniline) And Composite Poly(Aniline)−Poly(Styrenesulfonate) Membranes, D. L. Pile, Y. Zhang, Andrew C. Hillier

Andrew C. Hillier

The influence of oxidation state on the permeability of several probe molecules through conducting polymer membranes comprising composites of poly(aniline) and poly(styrenesulfonate) was examined in aqueous solution. Pure poly(aniline) membranes displayed a characteristic increase in permeability between reduced and half-oxidized states for neutrally charged phenol and negatively charged 4-hydroxybenzenesulfonate. In contrast, positively charged pyridine experienced decreased permeability through the membrane when poly(aniline) was switched from the reduced to the half-oxidized state. This behavior can be explained by a combination of oxidation-induced film swelling and the anion-exchange character of the positively charged membrane. The membrane composition was ...


Scanning Electrochemical Mapping Of Spatially Localized Electrochemical Reactions Induced By Surface Potential Gradients, Shrisudersan Jayaraman, Erin L. May, Andrew C. Hillier Jun 2014

Scanning Electrochemical Mapping Of Spatially Localized Electrochemical Reactions Induced By Surface Potential Gradients, Shrisudersan Jayaraman, Erin L. May, Andrew C. Hillier

Andrew C. Hillier

The influence of a surface potential gradient on the location and extent of electrochemical reactions was examined using a scanning electrochemical microscope. A linear potential gradient was imposed on the surface of a platinum-coated indium tin oxide electrode by applying two different potential values at the edges of the electrode. The applied potentials were used to control the location and extent of several electrochemical reactions, including the oxidation of Ru(NH3)62+, the oxidation of H2, and the oxidation of H2 in the presence of adsorbed CO. Scanning electrochemical mapping of these reactions was achieved by probing the feedback current ...


Organic Materials And Organic/Inorganic Heterostructures In Atom Probe Tomography, Derk Joester, Andrew C. Hillier, Yi Zhang, Ty J. Prosa Jun 2014

Organic Materials And Organic/Inorganic Heterostructures In Atom Probe Tomography, Derk Joester, Andrew C. Hillier, Yi Zhang, Ty J. Prosa

Andrew C. Hillier

Nano-scale organic/inorganic interfaces are key to a wide range of materials. In many biominerals, for instance bone or teeth, outstanding fracture toughness and wear resistance can be attributed to buried organic/inorganic interfaces. Organic/inorganic interfaces at very small length scales are becoming increasingly important also in nano and electronic materials. For example, functionalized inorganic nanomaterials have great potential in biomedicine or sensing applications. Thin organic films are used to increase the conductivity of LiFePO4 electrodes in lithium ion batteries, and solid electrode interphases (SEI) form by uncontrolled electrolyte decomposition. Organics play a key role in dye-sensitized solar cells ...


Resonance Quenching And Guided Modes Arising From The Coupling Of Surface Plasmons With A Molecular Resonance, Wei-Hsun Yeh, Joseph W. Petefish, Andrew C. Hillier Jun 2014

Resonance Quenching And Guided Modes Arising From The Coupling Of Surface Plasmons With A Molecular Resonance, Wei-Hsun Yeh, Joseph W. Petefish, Andrew C. Hillier

Andrew C. Hillier

In this paper, we describe experimental and modeling results that illucidate the nature of coupling between surface plasmon polaritons in a thin silver film with the molecular resonance of a zinc phthalocyanine dye film. This coupling leads to several phenomena not generally observed when plasmons are coupled to transparent materials. The increased absorption coefficient near a molecular resonance leads to a discontinuity in the refractive index, which causes branching of the plasmon resonance condition and the appearance of two peaks in the p-polarized reflectance spectrum. A gap exists between these peaks in the region of the spectrum associated with the ...


Three-Dimensional Atom Probe Tomography Of Oxide, Anion, And Alkanethiolate Coatings On Gold, Yi Zhang, Andrew C. Hillier Jun 2014

Three-Dimensional Atom Probe Tomography Of Oxide, Anion, And Alkanethiolate Coatings On Gold, Yi Zhang, Andrew C. Hillier

Andrew C. Hillier

We have used three-dimensional atom probe tomography to analyze several nanometer-thick and monomolecular films on gold surfaces. High-purity gold wire was etched by electropolishing to create a sharp tip suitable for field evaporation with a radius of curvature of layer, primarily consisting of water and atmospheric gases, was observed on a fresh tip. This sample exhibited crystalline lattice spacings consistent with the interlayer spacing of {200} lattice planes of bulk gold. A thin oxide layer was created on the gold surface via plasma oxidation, and the thickness and composition of this layer was measured. Clear evidence of a nanometer-thick oxide ...


Wavelength Tunable Surface Plasmon Resonance-Enhanced Optical Transmission Through A Chirped Diffraction Grating, Wei-Hsun Yeh, Justin Kleingartner, Andrew C. Hillier Jun 2014

Wavelength Tunable Surface Plasmon Resonance-Enhanced Optical Transmission Through A Chirped Diffraction Grating, Wei-Hsun Yeh, Justin Kleingartner, Andrew C. Hillier

Andrew C. Hillier

We report the construction and testing of a chirped diffraction grating, which serves as a substrate for surface plasmon-enhanced optical transmission. This grating possesses a spatial variation in both pitch and amplitude along its surface. It was created by plasma oxidation of a curved poly(dimethoxysilane) sheet, which resulted in nonuniform buckling along the polymer surface. A gold-coated replica of this surface elicited an optical response that consisted of a series of narrow, enhanced transmission peaks spread over the visible spectrum. The location and magnitude of these transmission peaks varied along the surface of the grating and coincided with conditions ...


High Rate Detection Of Volatile Products Using Differential Electrochemical Mass Spectrometry: Combining An Electrode-Coated Membrane With Hydrodynamic Flow In A Wall-Tube Configuration, Subramanian Venkatachalam, Robert J. Angelici, L. Keith Woo, Andrew C. Hillier Jun 2014

High Rate Detection Of Volatile Products Using Differential Electrochemical Mass Spectrometry: Combining An Electrode-Coated Membrane With Hydrodynamic Flow In A Wall-Tube Configuration, Subramanian Venkatachalam, Robert J. Angelici, L. Keith Woo, Andrew C. Hillier

Andrew C. Hillier

We present an experimental system that combines differential electrochemical mass spectrometry with hydrodynamic flow consisting of an impinging jet in a wall-tube configuration. This assembly allows simultaneous detection of electrochemical signals along with monitoring of dissolved gas species using differential electrochemical mass spectrometry under well-defined hydrodynamic conditions and over a wide range of mass transfer rates. The working electrode is deposited directly onto a thin, hydrophobic membrane, which also serves as the inlet to the mass spectrometer. This inlet provides extremely rapid mass detection as well as a high flux of products from the electrode surface into the mass spectrometer ...


Diffraction-Based Tracking Of Surface Plasmon Resonance Enhanced Transmission Through A Gold-Coated Grating, Wei-Hsun Yeh, Joseph W. Petefish, Andrew C. Hillier Jun 2014

Diffraction-Based Tracking Of Surface Plasmon Resonance Enhanced Transmission Through A Gold-Coated Grating, Wei-Hsun Yeh, Joseph W. Petefish, Andrew C. Hillier

Andrew C. Hillier

Surface plasmon resonance enhanced transmission through metal-coated nanostructures represents a highly sensitive yet simple method for quantitative measurement of surface processes and is particularly useful in the development of thin film and adsorption sensors. Diffraction-induced surface plasmon excitation can produce enhanced transmission at select regions of the visible spectrum, and wavelength shifts associated with these transmission peaks can be used to track adsorption processes and film formation. In this report, we describe a simple optical microscope-based method for monitoring the first-order diffracted peaks associated with enhanced transmission through a gold-coated diffraction grating. A Bertrand lens is used to focus the ...


Use Of Dispersion Imaging For Grating-Coupled Surface Plasmon Resonance Sensing Of Multilayer Langmuir–Blodgett Films, Wei-Hsun Yeh, Andrew C. Hillier Jun 2014

Use Of Dispersion Imaging For Grating-Coupled Surface Plasmon Resonance Sensing Of Multilayer Langmuir–Blodgett Films, Wei-Hsun Yeh, Andrew C. Hillier

Andrew C. Hillier

We report grating-coupled surface plasmon resonance measurements involving the use of dispersion images to interpret the optical response of a metal-coated grating. Optical transmission through a grating coated with a thin, gold film exhibits features characteristic of the excitation of surface plasmon resonance due to coupling with the nanostructured grating surface. Evidence of numerous surface plasmon modes associated with coupling at both front (gold/air) and back (gold/substrate) grating interfaces is observed. The influence of wavelength and angle of incidence on plasmon coupling can be readily characterized via dispersion images, and the associated image features can be indexed to ...


Combined Electrochemical Surface Plasmon Resonance For Angle Spread Imaging Of Multielement Electrode Arrays, Andrew C. Hillier, Chang Hoon Choi Jun 2014

Combined Electrochemical Surface Plasmon Resonance For Angle Spread Imaging Of Multielement Electrode Arrays, Andrew C. Hillier, Chang Hoon Choi

Andrew C. Hillier

A surface plasmon resonance imaging system combined with a multielement electrode array is described. An optical system with shaping optics is used to direct a wedge of light onto a gold-coated sample. The reflected light is detected in the form of an angle-spread image of the surface, with one direction denoting a variable incident angle and the other showing a span of locations along one lateral direction of the sample surface. At the proper incident angle, the angle-spread image shows the complete surface plasmon resonance curve over a span of locations on the surface. This imaging system is combined with ...


Surface Plasmon Resonance Enhanced Transmission Of Light Through Gold-Coated Diffraction Gratings, Bipin K. Singh, Andrew C. Hillier Jun 2014

Surface Plasmon Resonance Enhanced Transmission Of Light Through Gold-Coated Diffraction Gratings, Bipin K. Singh, Andrew C. Hillier

Andrew C. Hillier

Narrow peaks are observed in the transmission spectra of p-polarized light passing through a thin gold film that is coated on the surface of a transparent diffraction grating. The spectral position and intensity of these peaks can be tuned over a wide range of wavelengths by simple rotation of the grating. The wavelengths where these transmission peaks are observed correspond to conditions where surface plasmon resonance occurs at the gold−air interface. Light diffracted by the grating couples with surface plasmons in the metal film to satisfy the resonant condition, resulting in enhanced light transmission through the film. Notably, this ...


Construction Of A Tethered Poly(Ethylene Glycol) Surface Gradient For Studies Of Cell Adhesion Kinetics, K. Mougin, A. S. Ham, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier May 2014

Construction Of A Tethered Poly(Ethylene Glycol) Surface Gradient For Studies Of Cell Adhesion Kinetics, K. Mougin, A. S. Ham, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier

Andrew C. Hillier

Surface gradients can be used to perform a wide range of functions and represent a novel experimental platform for combinatorial discovery and analysis. In this work, a gradient in the coverage of a surface-immobilized poly(ethylene glycol) (PEG) layer is constructed to interrogate cell adhesion on a solid surface. Variation of surface coverage is achieved by controlled transport of a reactive PEG precursor from a point source through a hydrated gel. Immobilization of PEG is achieved by covalent attachment of the PEG molecule via direct coupling chemistry to a cystamine self-assembled monolayer on gold. This represents a simple method for ...


Construction Of Cell-Resistant Surfaces By Immobilization Of Poly(Ethylene Glycol) On Gold, K. Mougin, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier May 2014

Construction Of Cell-Resistant Surfaces By Immobilization Of Poly(Ethylene Glycol) On Gold, K. Mougin, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier

Andrew C. Hillier

Considerable effort has been expended in efforts to create surfaces that resist the adsorption of proteins and cells for biomedical applications. The majority of such work has focused on surfaces constructed from bulk polymers or thin polymer films. However, the fabrication of surfaces via self-assembled monolayers (SAMs) has attracted considerable interest because of the robustness, versatility, and wide-ranging applicability of these materials. SAMs are particularly appealing for biological systems where well-defined surface chemistries can be created to facilitate coupling, biorecognition, or cell adhesion along with a host of other applications in biochemistry and biotechnology.