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PubMed2003

Surface functionalization of polypyrrole film with glucose oxidase and viologen.

A surface modification technique was developed for the functionalization of polypyrrole (PPY) film with glucose oxidase (GOD) and viologen moieties. The PPY film was first graft copolymerized with acrylic acid (AAc) and GOD was then covalently immobilized through the amide linkage formation between the amino groups of the GOD and the carboxyl groups of the grafted AAc polymer chains in the presence of a water-soluble carbodiimide. Viologen moieties could also be attached to the PPY film via graft-copolymerization of vinyl benzyl chloride with the PPY film surface followed by reaction with 4,4'-bipyridine and alpha,alpha'-dichloro-p-xylene. X-ray photoelectron spectroscopy (XPS) was used to characterize the PPY films after each surface modification step. Increasing the AAc graft concentration would allow a greater amount of GOD to be immobilized but this would decrease the electrical conductivity of the PPY film. The activity of the immobilized GOD was compared with that of free GOD and the kinetic effects were also studied. The immobilized GOD was found to be less sensitive to temperature deactivation as compared to the free GOD. The results showed that the covalent immobilization technique offers advantages over the technique involving the entrapment of GOD in PPY films during electropolymerization. The presence of viologen in the vicinity of the immobilized GOD also enabled the GOD-catalyzed oxidation of glucose to proceed under UV irradiation in the absence of O(2).

Acrylates↗
PubMed2002

Development and application of multicomponent edible coatings and films: a review.

Combining the advantages of polysaccharides, proteins and/or lipids offers multicomponent edible films and coatings good mass transfer barrier properties. Multicomponent edible films and coatings could be beneficial to the food industry by leading to innovative applications. The barrier properties of these systems strongly depend upon their structure and chemistry, the interaction between different film components as well as surrounding environment conditions. Future researches on these multicomponent systems need to concentrate on the following goals: (1) investigation of the optimal film compositions and specific film-forming conditions for different food systems; (2) study of the film responses in their barrier properties to environmental factors such as RH and temperature; (3) fundamental research of the mechanism of mass transfer and the interaction of different films components and foods; (4) exploration of the feasibility of potential applications in the food industry.

Food Handling↗
PubMed1996

Computed radiography and film digitizer inputs to an intensive care unit teleradiology system: an image quality comparison.

RATIONALE AND OBJECTIVES: We compared computed radiography (CR) with a film digitizer as an image input device for transmitting radiographs to intensive care unit (ICU) displays. METHODS: Limiting spatial resolution and low-contrast detectability performance were determined for a 600-speed screen-film combination and CR films. The same image data were transmitted to ICU displays directly from the CR or by digitizing the conventional film. RESULTS: CR resolution ranged from 2.5 to 3 line pairs per millimeter (Ip/ mm) depending on cassette size. Display station resolution for the CR image data was 1.5-1.9 lp/mm, but improved resolution could be achieved using display magnification modes. Film digitization resulted in a loss of resolution. Direct transmission of CR image data to display stations gave low-contrast detectability similar to that obtained with CR film. CONCLUSION: ICU teleradiology displays that use CR, rather than film digitizers, offer improved image quality and superior operational efficiency.

Intensive Care Units↗
PubMed1998

Computed radiography versus screen-film mammography in detection of simulated microcalcifications: a receiver operating characteristic study based on phantom images.

RATIONALE AND OBJECTIVES: The authors compare a 43-micron computed radiographic system with a mammographic screen-film system for detection of simulated microcalcifications in an observer-performance study. MATERIALS AND METHODS: The task of detecting microcalcifications was simulated by imaging aluminum wire segments (200-500 microns in length; 100, 125, or 150 microns in diameter) that overlapped with tissue background structures produced by beef brisket. A total of 288 such simulations were generated and examined with both computed radiography and conventional screen-film mammography techniques. Computed radiography was performed with high-resolution plates, a 43-micron image reader, and a 43-micron laser film printer. Computed radiographic images were printed with simple contrast enhancement and compared with screen-film images in a receiver operating characteristic study in which experienced readers detected and scored the simulated microcalcifications. Observer performance was quantitated and compared by computing the area under the receiver operating characteristic curve. RESULTS: Although the resolution of the computed radiography system was better than that of commercial systems, it fell short of that of screen-film systems. For the 100-micron microcalcifications, the difference in the average area under the curve was not statistically significant, but it was significant for the larger simulated microcalcifications: the average area under the curve was 0.58 for computed radiography versus 0.76 for screen-film imaging for the 125-micron microcalcifications and 0.83 versus 1.00, respectively, for the 150-micron microcalcifications. CONCLUSION: Observer performance in the detection of small simulated microcalcifications (100-150 microns in diameter) is better with screen-film images than with high-resolution computed radiographic images.

Breast Diseases↗
PubMed2003

Biosensor for dopamine based on stabilized lipid films with incorporated resorcin[4]arene receptor.

This work reports a technique for the stabilization after storage in air of a lipid film with incorporated resorcin[4]arene receptor based biosensor for dopamine. Microporous filters composed of glass fibers (nominal pore sizes, 0.7 and 1.0 microm) were used as supports for the formation and stabilization of these devices and the lipid film is formed on the filter by polymerization prior its use. Methacrylic acid was the functional monomer, ethylene glycol dimethacrylate was the crosslinker and 2,2'-azobis-(2-methylpropionitrile) was the initiator. The stability of the lipid films by incorporation of a receptor for the preparation of stabilized lipid film biosensor is studied throughout this work. The response towards dopamine of the present stabilized for repetitive uses lipid membrane biosensor composed of dipalmitoyl phosphatidylcholine and dipalmitoyl phosphatidic acid was compared with planar freely suspended bilayer lipid membranes (BLMs). The stabilized lipid membranes provided similar artificial ion gating events as BLMs in the form of transient signals and can function for repetitive uses after storage in air. However, the response of the stabilized lipid films was slower than that of the freely suspended BLMs. This will allow the practical use of the techniques for chemical sensing based on lipid films and commercialization of these devices, because it is now possible to prepare stabilized lipid film based biosensors and store them in the air.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2006

AES studies on the Ti/N compositionally gradient film deposited onto Ti-6Al-4V alloy by reactive DC sputtering.

Deposition of Ti/N compositionally gradient film onto Ti-6Al-4V alloy substrates was carried out by reactive DC sputtering, not only to improve the blood compatibility of the alloy but also to relax the stress concentrated at the interface between the film and the alloy substrate. The compositional gradient was realized by varying continuously the nitrogen content in Ar-N2 sputter gas during deposition. In Auger electron spectroscopy (AES) analysis, Auger spectra were acquired in the N(E) mode using the beam brightness modulation (BBM) method to overcome the problem of the peak overlap of the principal Auger nitrogen transition peak (N-KLL) with one of titanium peaks (Ti-LMM). The deposited film appeared to be uniform and adhesive. TiN formation at the surface of the film was assumed, because of its yellow gold color and the X-ray diffraction (XRD) pattern for it. Under scanning electron microscopy, it was found that the surface had fine particles dispersed on a smooth accumulated deposit and that this depositing method improved the structural property of the film at the surface. According to AES in-depth profiles, the nitrogen (N) concentration in the film gradually decreased in the depth direction from the surface toward the alloy, confirming that a Ti/N compositionally gradient film had formed on the alloy substrate.

Journal Article↗
PubMed1991

Surfactant-intercalated clay films for electrochemical catalysis. Reduction of trichloroacetic acid.

Composite films made from insoluble dialkyldimethylammonium surfactants and clay colloids were evaluated for electrochemical catalysis. When cast on pyrolytic graphite (PG) electrodes from chloroform, the films act as charge-transfer barriers toward multivalent electroactive ions in solution. They take up ions with hydrophobic ligands, e.g. tris-(2,2'-bipyridyl)cobalt(II). To make catalytic electrodes, water-insoluble cobalt and iron phthalocyanines (CoPc and FePc) were dissolved in surfactant-clay dispersions in chloroform and cast on PG. Films containing CoPc were 35-fold more active than FePc films for catalytic reduction of trichloroacetic acid. CoPc films decreased overpotential for reduction of trichloroacetic acid by about 0.5 V compared to 0.05 V for FePc. These MPc films gave stable catalytic currents for at least 10 days. Catalytic current vs temperature plots for reduction of trichloroacetic acid showed linear branches with intersection points close to reported gel-to-liquid crystal-phase transition temperatures. Charge transport was faster in the liquid crystal than the gel phase of the films. Observation of phase transitions suggests a multibilayer structure.

Aluminum Silicates↗
PubMed1994

Films formed by oxidation of ferrocene at platinum electrodes.

Oxidation of ferrocene in acetonitrile resulted in films on Pt electrodes under voltammetric conditions. Films were more readily formed with tetrabutylammonium tetrafluoroborate as the electrolyte than with perchlorate salts. No films were detected when ferrocene was oxidized in aqueous 0.05 M cetyltrimethylammonium bromide (CTAB). Analysis of the films by FT-IR and Auger spectroscopy confirmed iron-containing oxidation products on Pt, presumably from chemical reactions of ferricinium ions. Oxidation of 50-100 mM ferrocene in acetonitrile on Pt yielded insoluble precipitates. Analyses by MS, FT-IR, and UV-visible (water extract), suggested a mixture of oligomeric material and a small fraction of ferricinium ions. Film formation had much less influence on voltammograms on 12.5-micron-radius Pt microdisks than on 0.5-mm-radius Pt. This is consistent with the smaller sensitivity of microelectrodes to chemical reactions following charge transfer. The smaller apparent heterogeneous rate constants (k zero') found for ferrocene on macroelectrodes than on microelectrodes could possibly be influenced by film formation on larger Pt electrodes. Correlations between macro- and microelectrode kinetic data suggest that macroelectrode k zero' values may be valid in a relative sense when ohmic drop is negligible. Bias in k zero's on conventional-sized electrodes should be small in solutions giving minimal film formation, such as micellar CTAB.

Electrochemistry↗
PubMed2002

In situ FT-IR measurements of competitive vapor adsorption into porous thin films containing silica nanoparticles.

Vapor adsorption into porous ultrathin films on a gold surface is investigated with in situ surface plasmon resonance (SPR) and polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The thin films are prepared by the electrostatic self-assembly of oppositely charged poly(L-lysine) (PL) and silica nanoparticles on a chemically modified gold surface. Characterization with ex situ SPR and PM-IRRAS demonstrates the buildup of multiple PL/SiO2 bilayers as well as an excellent correlation between the quantitative results from these two techniques. In situ vapor adsorption experiments with these thin films show evidence of porosity, reproducibility, and rapid reversibility. Exposure to acetone vapor (P/P0 = 0.032) causes the film to adsorb 9% acetone by volume, which corresponds to coverage of approximately one-half of the silica nanoparticle surface area. In situ PM-IRRAS provides much information about the molecular interactions occurring in the film upon adsorption or desorption of vapors. Dosing with a mixture of vapors leads to a competition for adsorption into the film, and PM-IRRAS results show that acetone slightly outcompetes nitromethane. These experiments with nanoparticle thin films demonstrate the advantages of using in situ PM-IRRAS for studying reversible adsorption in the presence of vapor mixtures.

Journal Article↗
PubMed2003

Optical sensor for amine vapors based on dimer-monomer equilibrium of indium(III) octaethylporphyrin in a polymeric film.

A novel transduction chemistry for the development of a polymer film-based optical sensor that responds reversibly to gas-phase amine species at sub-ppm levels is described. The sensor is based on the equilibrium of a indium(III) octaethylporphyrin hydroxide ion-bridged dimer species with corresponding monomeric porphyrins within a thin poly(vinyl chloride) film as a function of the level of volatile amine in the surrounding gas phase. The presence of amines causes the dimeric species to be converted to monomer via the ligation of the amine with the In(III) center of the porphyrin structure. This yields a significant change in the visible absorption spectrum of the film, with a decrease in the intensity of the Soret band corresponding to the dimer (lambdamax = 390 nm) and a concomitant increase in the Soret band for the monomer lambdamax = 406-408 nm). Response to different amines is based on their relative partition coefficient into the polymer film and their strength of axial ligation reactions, with a selectivity pattern of 1-butylamine > 1-propylamine > pyridine > triethylamine > ethylamine > methylamine > diethylamine > tert-butylamine > ammonia. It is further shown that a significant concentration of dimeric species within the polymer film can only be achieved if appropriate amounts of lipophilic anionic sites are also incorporated into the polymer in the form of a tetraphenylborate derivative and the resulting film is equilibrated briefly with water prior to gas-phase measurements. With optimized film compositions, 1-butylamine can be detected in the gas phase to levels approaching 0.1 ppm, while less lipophilic ammonia can be monitored down to 10 ppm, with fully reversible responses to each species. A simple mathematical model for the response of the amine sensor is presented and shown to predict the optical behavior observed.

Amines↗
PubMed2003

Total internal reflection fluorescence-correlation spectroscopy study of molecular transport in thin sol-gel films.

Total internal reflection fluorescence correlation spectroscopy is used to measure mass transport rates through thin sol-gel films. Fluctuations in the fluorescence signal derive from molecular statistics due to the small number (approximately 1000) of rhodamine 6G dye molecules in the observation region. Autocorrelation of the fluctuating signal is fit to a model describing diffusion in the evanescent wave excitation. Silica sol-gel films were prepared by dip-coating 27-nm porous silica particles, which were synthesized by a base-catalyzed sol-gel method, onto microscope slides. The measured diffusivities ranged from 1 to 2 orders of magnitude slower than free diffusion and decreased with increasing number of dips used to prepare the film. Scanning electron microscopy (SEM) was used to examine the film structure and showed that increasing the number of dips produced more uniform and well-ordered films. To determine what role the dip-coating process plays in inducing order, deposited films were further dipped into ethanol containing no particles. These films were annealed by this process and become more ordered, as determined by SEM, and show a corresponding reduction in the molecular diffusivity.

Journal Article↗
PubMed2004

Quartz crystal microbalance and infrared reflection absorption spectroscopy characterization of bisphenol A absorption in the poly(acrylate) thin films.

The absorption process of bisphenol A (BPA) in a number of poly(acrylate) thin films, such as poly(2-methoxyethyl acrylate) (PMEA), poly(ethyl acrylate) (PEA), poly(n-butyl methacrylate) (PBMA), and poly(methyl methacrylate) (PMMA), has been investigated by quartz crystal microbalance (QCM) and infrared reflection absorption spectroscopy (IRRAS) measurements. Both QCM and IRRAS measurements show that the BPA molecules absorb in PMEA, PEA, and PBMA thin films but not in PMMA thin film. The differences in the BPA absorption behavior are mainly attributed to the difference in the glass transition temperature (T(g)) between these polymers. This absorption behavior also depends on the BPA concentration and polymer film thickness. Furthermore, IRRAS characterization demonstrates that the hydrogen bonding is formed between the hydroxyl group in BPA and the carbonyl group in the poly(acrylate) thin films. BPA molecule absorbed in these polymer thin films can be removed by ethanol rinse treatment. By optimizing experimental conditions for the QCM electrode modified by PMEA thin film, detection limitation of approximately 1 ppb for BPA can be realized by the in situ QCM measurement. This method is expected to be a sensitive in situ detection way for trace BPA in the environmental study.

Journal Article↗
PubMed2004

Ultraflat carbon film electrodes prepared by electron beam evaporation.

A facile method for the preparation of thin-film carbon electrodes by electron beam evaporation onto highly doped silicon is presented. The physical and electrochemical properties of these films both before and after postdeposition pyrolysis are investigated. Raman spectroscopy establishes the amorphous structure of the nonpyrolyzed carbon films and confirms the formation of graphitic carbon after pyrolysis at 1000 degrees C. Scanning force microscopy reveals the root-mean-square roughness of nonpyrolyzed films to be approximately 1 A, while pyrolyzed films exhibit an increased roughness of approximately 4 A. The electrochemical behavior of the electrodes resembles glassy carbon, with measured heterogeneous electron-transfer rate constants among the highest measured for thin carbon films. These carbon film electrodes will potentially find applications in such fields as molecular electronics and scanning probe microscopy of adsorbed species.

Journal Article↗
PubMed2004

Electrogenerated chemiluminescence from R(bpy)3(2+) ion-exchanged in carbon nanotube/perfluorosulfonated ionomer composite films.

The electrochemistry and electrogenerated chemiluminescence (ECL) of ruthenium(II) tris(bipyridine) (Ru(bpy)(3)(2+)) ion-exchanged in carbon nanotube (CNT)/Nafion composite films were investigated with tripropylamine (TPA) as a coreactant at a glassy carbon (GC) electrode. The major goal of this work was to investigate and develop new materials and immobilization approaches for the fabrication of ECL-based sensors with improved sensitivity, reactivity, and long-term stability. Ru(bpy)(3)(2+) could be strongly incorporated into Nafion film, but the rate of charge transfer was relative slow and its stability was also problematic. The interfusion of CNT in Nafion resulted in a high peak current of Ru(bpy)(3)(2+) and high ECL intensity. The results indicated that the composite film had more open structures and a larger surface area allowing faster diffusion of Ru(bpy)(3)(2+) and that the CNT could adsorb Ru(bpy)(3)(2+) and also acted as conducting pathways to connect Ru(bpy)(3)(2+) sites to the electrode. In the present work, the sensitivity of the ECL system at the CNT/Nafion film-modified electrodes was more than 2 orders of magnitude higher than that observed at a silica/Nafion composite film-modified electrode and 3 orders of magnitude higher than that at pure Nafion films. The CNT/Nafion composite film-modified GC electrodes also exhibited long-term stability.

Journal Article↗
PubMed2005

Molecular depth profiling of multilayer polymer films using time-of-flight secondary ion mass spectrometry.

The low penetration depth and high sputter rates obtained using polyatomic primary ions have facilitated their use for the molecular depth profiling of some spin-cast polymer films by secondary ion mass spectrometry (SIMS). In this study, dual-beam time-of-flight (TOF) SIMS (sputter ion, 5 keV SF(5)(+); analysis ion, 10 keV Ar(+)) was used to depth profile spin-cast multilayers of poly(methyl methacrylate) (PMMA), poly(2-hydroxyethyl methacrylate) (PHEMA), and trifluoroacetic anhydride-derivatized poly(2-hydroxyethyl methacrylate) (TFAA-PHEMA) on silicon substrates. Characteristic positive and negative secondary ions were monitored as a function of depth using SF(5)(+) primary ion doses necessary to sputter through the polymer layer and uncover the silicon substrate (>5 x10(14) ions/cm(2)). The sputter rates of the polymers in the multilayers were typically less than for corresponding single-layer films, and the order of the polymers in the multilayer affected the sputter rates of the polymers. Multilayer samples with PHEMA as the outermost layer resulted in lowered sputter rates for the underlying polymer layer due to increased ion-induced damage accumulation rates in PHEMA. Additionally, the presence of a PMMA or PHEMA overlayer significantly decreased the sputter rate of TFAA-PHEMA underlayers due to ion-induced damage accumulation in the overlayer. Typical interface widths between adjacent polymer layers were 10-15 nm for bilayer films and increased with depth to approximately 35 nm for the trilayer films. The increase in interface width and observations using optical microscopy showed the formation of sputter-induced surface roughness during the depth profiles of the trilayer polymer films. This study shows that polyatomic primary ions can be used for the molecular depth profiling of some multilayer polymer films and presents new opportunities for the analysis of thin organic films using TOF-SIMS.

Acetic Anhydrides↗
PubMed2005

Use of attenuated total reflection infrared spectroscopy for analysis of partitioning of solutes between thin films and solution.

The paper examines attenuated total reflection (ATR) spectroscopy as a tool for quantifying the partitioning of small molecular species between a solution and a thin film, while the film is directly exposed to the solution for equilibration. For the case of a thin film having a thickness substantially smaller than the decay length of the evanescent wave, we developed suitable linear relationships that relate the measured absorption of the characteristic band to the concentration of the species under study in the film and in solution. In the application of ATR-Fourier transform infrared spectroscopy, the method is particularly suitable for films a few tens to hundreds of nanometers thick and for solutes that preferentially partition into the film. As an example, the partitioning isotherm of 1-pentanol between water and a thin polyamide film separated from a reverse osmosis membrane was determined experimentally, and the limitations of the method are discussed.

Journal Article↗
PubMed2006

Method for measuring thickness of dielectric films using microdielectric fringe-effect sensors.

A method for noninvasive thickness measurements of dielectric films using fringe-effect (FE) sensors is developed and experimentally validated. The fringing electrical field, created by electrodes microfabricated at the film substrate, depends on the film thickness and dielectric permittivity of the film under test (FUT). The unknown film thickness is estimated by matching the theoretical prediction of thickness-dependent sensor admittance with the measured value. In the case of FE sensors with spatially periodic, interdigitated electrode (IDE) configuration, the admittance prediction is simplified, which allows for the real-time measurements of changing thickness. The developed method can be used to continuously measure the changing dielectric permittivity of the FUT material, which makes it possible to determine the thickness of films of changing dielectric properties, caused by chemical or other transformations. The application of the developed method is demonstrated experimentally by measuring the thickness of silicon nitride film deposited in several increments on the quartz substrate of the IDE sensor. In the expected range of sensor sensitivity, the results show an excellent agreement with the independent thickness measurements.

Journal Article↗
PubMed2006

Direct writing of metal nanoparticle films inside sealed microfluidic channels.

Herein we demonstrate the ability to pattern Ag nanoparticle films of arbitrary geometry inside sealed PDMS/TiO2/glass microfluidic devices. The technique can be employed with aqueous solutions at room temperature under mild conditions. A 6 nm TiO2 film is first deposited onto a planar Pyrex or silica substrate, which is subsequently bonded to a PDMS mold. UV light is then exposed through the device to reduce Ag+ from an aqueous solution to create a monolayer-thick film of Ag nanoparticles. We demonstrate that this on-chip deposition method can be exploited in a parallel fashion to synthesize nanoparticles of varying size by independently controlling the solution conditions in each microchannel in which the film is formed. The film morphology was checked by atomic force microscopy, and the results showed that the size of the nanoparticles was sensitive to solution pH. Additionally, we illustrate the ability to biofunctionalize these films with ligands for protein capture. The results indicated that this could be done with good discrimination between addressed locations and background. The technique appears to be quite general, and films of Pd, Cu, and Au could also be patterned.

Coated Materials, Biocompatible↗