| 1. |
|
|
| 2. |
- Hook, F.F, et al.
(author)
-
A comparative study of protein adsorption on titanium oxide surfaces using in situ ellipsometry, optical waveguide lightmode spectroscopy, and quartz crystal microbalance/dissipation
- 2002
-
In: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 24:2, s. 155-170
-
Journal article (peer-reviewed)abstract
- The adsorption kinetics of three model proteins - human serum albumin, fibrinogen and hemoglobin - has been measured and compared using three different experimental techniques: optical waveguide lightmode spectroscopy (OWLS), ellipsometry (ELM) and quartz crystal microbalance (QCM-D). The studies were complemented by also monitoring the corresponding antibody interactions with the pre-adsorbed protein layer. All measurements were performed with identically prepared titanium oxide coated substrates. All three techniques are suitable to follow in-situ kinetics of protein-surface and protein-antibody interactions, and provide quantitative values of the adsorbed adlayer mass. The results have, however, different physical contents. The optical techniques OWLS and ELM provide in most cases consistent and comparable results, which can be straightforwardly converted to adsorbed protein molar ('dry') mass. QCM-D, on the other hand, produces measured values that are generally higher in terms of mass. This, in turn, provides valuable, complementary information in two respects: (i) the mass calculated from the resonance frequency shift includes both protein mass and water that binds or hydrodynamically couples to the protein adlayer, and (ii) analysis of the energy dissipation in the adlayer and its magnitude in relation to the frequency shift (c.f. adsorbed mass) provides insight about the mechanical/structural properties such as viscoelasticity. © 2002 Elsevier Science B.V. All rights reserved.
|
|
| 3. |
- Hook, F., et al.
(author)
-
Variations in coupled water, viscoelastic properties, and film thickness of a Mefp-1 protein film during adsorption and cross-linking: a quartz crystal microbalance with dissipation monitoring, ellipsometry, and surface plasmon resonance study
- 2001
-
In: Analytical Chemistry. - 0003-2700 .- 1520-6882. ; 73:24, s. 5796-804
-
Journal article (peer-reviewed)abstract
- We have measured the time-resolved adsorption kinetics of the mussel adhesive protein (Mefp-1) on a nonpolar, methyl-terminated (thiolated) gold surface, using three independent techniques: quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance, and ellipsometry. The QCM-D and ellipsometry data shows that, after adsorption to saturation of Mefp-1, cross-linking of the protein layer using NaIO4 transforms it from an extended (approximately 20 nm), water-rich, and hydrogel-like state to a much thinner (approximately 5 nm), compact, and less water-rich state. Furthermore, we show how quantitative data about the thickness, shear elastic modulus, and shear viscosity of the protein film can be obtained with the QCM-D technique, even beyond the Sauerbrey regime, if frequency (f) and energy dissipation (D) measurements measured at multiple harmonics are combined with theoretical simulations using a Voight-based viscoelastic model. The modeling result was confirmed by substituting H2O for D2O. As expected, the D2O substitution does not influence the actual adsorption behavior, but resulted in expected differences in the estimated effective density and shear viscosity. These results provide new insight and understanding about the adsorption kinetics and crosslinking behavior of Mefp-1. They also demonstrate how the above three techniques complement each other for biomolecule adsorption studies.
|
|
| 4. |
- Johansson, S, et al.
(author)
-
CO oxidation bistability diagrams for Pt/CeOx and Pt/SiO2 model catalysts prepared by electron-beam lithography
- 2001
-
In: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 201:2, s. 275-285
-
Journal article (peer-reviewed)abstract
- The CO oxidation bistability diagrams (i.e., the interval of gas mixing ratio beta drop P-CO/(P-CO + P-O2) vs temperature for which a bistability exists) have been determined for different electron beam lithography (EBL) fabricated supported model catalysts. Three different samples were studied, one Pt/SiO2 sample and two Pt/CeOx samples, where the support type, particle size, and interface length were varied independently. The kinetic bistability is an inherent property of the CO oxidation on Pt at certain gas mixtures and temperatures, and we find that the actual position of the bistable region is a very sensitive tool to measure differences in reaction kinetics on different samples. The bistable region is shifted considerably along the gas mixing ratio axis, beta, between the three samples (at constant temperature). Simulations show that the experimental results can be understood by introducing an oxygen reactant supply via the CeOx, support (spillover), which does not exist for SiO2. This extra supply of oxygen will maintain a high CO conversion rate up to higher relative CO partial pressures on ceria samples (by suppressing the CO poisoning effect). Energy barriers for O diffusion on CeOx, and the attachment across the Pt/CeOx interface have been estimated. The formation of a less reactive Pt state under oxidizing conditions is discussed. (C) 2001 Academic Press.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Werdinius, C, et al.
(author)
-
Nanofabrication of planar model catalysts by colloidal lithography : Pt/ceria and Pt/alumina
- 2003
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:2, s. 458-468
-
Journal article (peer-reviewed)abstract
- We present a novel method, called colloidal lithography, to prepare well-defined model catalysts on planar supports. The method facilitates fabrication of monodisperse catalyst particles with variable, well-defined size, shape, and interparticle distance. The chemical and structural composition of the constituents (i.e., catalyst particles and support materials) maybe independently varied. Large batches of model catalysts may be made in short processing times, with the dimensions of the samples only limited by the physical dimension of available support material, the processing vacuum systems, and so forth. Here we employed 2 in. Si wafers cut into 1 x 1 cm(2) pieces as the primary lithography support, onto which the support (ceria and alumina) and active catalyst materials (Pt in this case) were deposited. A detailed chemical and structural characterization is presented of the individual steps in the fabrication process. The oxygen plasma used to remove the colloidal mask residues is shown to lead to substantial but reversible Pt oxidation. As a probe reaction, to validate the nanofabrication process, CO oxidation measurements were performed on 130 nm Pt particles on an alumina or a ceria support. The reactivity measurements are in good agreement with literature data and suggest a satisfactory performance of the colloidal lithography model catalysts.
|
|
| 9. |
- Österlund, Lars, 1967-, et al.
(author)
-
Reactivity of Pt/ceria and Pt/alumina planar model catalysts prepared by colloidal lithography
- 2003
-
In: Journal of Catalysis. - 0021-9517 .- 1090-2694. ; 215:1, s. 94-107
-
Journal article (peer-reviewed)abstract
- We report on the structure, chemical state, and catalytic activity of nanofabricated, planar Pt/ceria and Pt/alumina model catalysts prepared by colloidal lithography. Employing extended etching times, catalyst particles are fabricated that are much smaller than the size of the polystyrene colloidal particle mask. Using CO oxidation as a probe reaction, the influence of various pretreatments has been studied. We find that the H-2/O-2 pretreatment deteriorates the reactivity on Pt/alumina, which is accompanied by blocking of the high-temperature CO adsorption sites as seen by TPD. After prolonged reactions the Pt/ceria particles show pronounced restructuring, indicating a low-temperature, reaction-induced, strong metal-support interaction, where ceria is decorating the Pt particles. In contrast, after an identical reaction history the Pt/alumina particles become facetted. The nanofabrication approach allows us to attribute the structural changes on individual particles to the integrated, macroscopic catalytic response. (C) 2003 Elsevier Science (USA). All rights reserved.
|
|
