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David G. Castner - One of the best experts on this subject based on the ideXlab platform.
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comparison of native extracellular matrix with Adsorbed Protein films using secondary ion mass spectrometry
Langmuir, 2007Co-Authors: Heather E Canavan, Buddy D Ratner, Daniel J Graham, Xuanhong Cheng, David G. CastnerAbstract:In the past decade, the temperature-responsive behavior of poly(N-isopropyl acrylamide) (pNIPAM) has come to be recognized as a convenient method for the nondestructive harvest of confluent cell layers. Recently, we have utilized this nondestructive cell harvest method as a means to ascertain the nature of the extracellular matrix (ECM) secreted from cells. In this work, we compare the ECM obtained after cell liftoff to individual ECM Proteins Adsorbed directly onto RF-plasma-deposited pNIPAM (ppNIPAM). Using X-ray photoelectron spectroscopy, we find that the composition of ppNIPAM post-cell liftoff surfaces is consistent with those of the ppNIPAM post-Protein adsorption surface, both of which differ from control surfaces. Using principal component analysis of positive-ion time-of-flight secondary ion mass spectrometry (ToF-SIMS) data, we show that the major ECM Proteins examined can effectively be identified from their amino acid compositions. By comparing the positive-ion ToF-SIMS data from each of the ppNIPAM post-Protein adsorption surfaces to that of ppNIPAM post-cell liftoff, we find that ppNIPAM post-cell liftoff surfaces are distinctly separate from fibronectin (FN). This result is consistent with our previous observation using immunoassay that FN is clearly associated with the cell sheet after low-temperature liftoff from ppNIPAM.
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preserving the structure of Adsorbed Protein films for time of flight secondary ion mass spectrometry analysis
Journal of Biomedical Materials Research Part A, 2003Co-Authors: Nan Xia, David G. CastnerAbstract:The characterization of Adsorbed Protein films with ultrahigh vacuum (UHV) surface analysis techniques requires dehydration of the samples, which can cause significant alterations in Protein structure. It is desirable to preserve the structure of Adsorbed Protein films during drying, so UHV analysis could be done in a state that is more representative of Proteins' actual structure in the aqueous environment. In this study, two methods, trehalose protection and glutaraldehyde fixation, were explored for their feasibility in preserving Adsorbed Protein structure for a powerful UHV surface analysis technique, time-of-flight secondary ion mass spectrometry (ToF-SIMS). Trehalose protection had shown some promise for ToF-SIMS analysis in our previous study and was further examined with the model Protein fibrinogen in this study. Using the combination of principal component analysis (PCA) and static ToF-SIMS analysis, we found that trehalose protection could reduce the conformation change of fibrinogen upon drying, and prevent it from unfolding and exposing hydrophobic domains. Moreover, when the Adsorbed Protein film became more densely packed, the drying-induced changes in Protein structure were reduced. Thus, the protection afforded by trehalose coating was more significant at lower Protein surface concentrations. The other method, glutaraldehyde fixation, was used in ToF-SIMS analysis for the first time. The ϵ-amino group of lysine was identified as the major reactive group in the Protein structure toward glutaraldehyde fixation. Structural differences observed between fibrinogen films that were glutaraldehyde fixed before drying and after drying were similar to those observed between trehalose-protected and-unprotected dried fibrinogen films. Glutaraldehyde fixation was found to be a viable, alternative stabilizing method to trehalose protection for ToF-SIMS analysis. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 179–190, 2003
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characterizing multicomponent Adsorbed Protein films using electron spectroscopy for chemical analysis time of flight secondary ion mass spectrometry and radiolabeling capabilities and limitations
Biomaterials, 2003Co-Authors: M S Wagner, Thomas A. Horbett, David G. CastnerAbstract:Characterization of complex Adsorbed Protein films is a critical aspect of biomaterials science, particularly in understanding the in vivo response to biomaterials. The surface analysis techniques electron spectroscopy for chemical analysis (ESCA) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) are particularly suited to the analysis of complex Adsorbed Protein films due to their wide applicability to a variety of materials. We have investigated the applicability of ESCA for studying the structure of Adsorbed serum and plasma Protein layers. ESCA was able to monitor the thickness of the Adsorbed Protein film. Due to its chemical specificity, ToF-SIMS was used to estimate the composition of the plasma and serum Protein layers by comparison of their spectra with the spectra of single Protein films. The limit of detection of ToF-SIMS for the plasma Protein fibrinogen was determined by comparison with independent radiolabeled fibrinogen adsorption measurements. While ToF-SIMS was able to determine some qualitative trends in the composition of the plasma Protein films as a function of adsorption time, the detection limit of the minor components in multicomponent Adsorbed Protein films ultimately limits the ability of ToF-SIMS to quantify the composition of these films. However, both ESCA and ToF-SIMS can provide useful information on Adsorbed plasma Protein films without further sample treatment. This study outlines the strengths and weaknesses of ESCA and ToF-SIMS for studying multicomponent Adsorbed plasma Protein films.
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quantitative time of flight secondary ion mass spectrometry for the characterization of multicomponent Adsorbed Protein films
Applied Surface Science, 2003Co-Authors: Matthew Scott Wagner, Thomas A. Horbett, Mingchao Shen, David G. CastnerAbstract:Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is ideal for the characterization of Adsorbed Proteins due to its chemical specificity and surface sensitivity. We have employed ToF-SIMS and multivariate analysis to determine the surface composition of Adsorbed Protein films from binary mixtures, blood serum, and blood plasma. Good correlation between ToF-SIMS data and independent radiolabeling studies was achieved for binary mixtures, though these results depended on the substrate. Qualitative insight into the composition of the serum and plasma Protein films was obtained via comparison to standard single Protein film spectra. ToF-SIMS and multivariate analysis were able to measure the surface composition of multicomponent Adsorbed Protein films.
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characterization of Adsorbed Protein films using time of flight secondary ion mass spectrometry and multivariate analysis
Applied Surface Science, 2003Co-Authors: M S Wagner, David G. CastnerAbstract:The complexity of the mass spectra obtained by static time-of-flight-secondary ion mass spectrometry (ToF-SIMS) demands high-throughput data analysis techniques that rapidly process and interpret the resulting data. We have used ToF-SIMS to analyze Adsorbed Protein films. Positive ion mass spectra from different Protein films are challenging to differentiate due to the absence of unique, identifying peaks between the different spectra. Therefore, the multivariate pattern recognition techniques principal component analysis (PCA) and linear discriminant analysis (LDA) have been employed to differentiate the spectra of different Proteins and understand the major sources of variation in these spectra. Because of its supervised nature, LDA enhanced discrimination between groups and classification of unknowns when compared with PCA. However, PCA was able to provide better information on the sources of variation in the data set. Both PCA and LDA are important in the analysis of static ToF-SIMS spectra from organic samples.
M S Wagner - One of the best experts on this subject based on the ideXlab platform.
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characterizing multicomponent Adsorbed Protein films using electron spectroscopy for chemical analysis time of flight secondary ion mass spectrometry and radiolabeling capabilities and limitations
Biomaterials, 2003Co-Authors: M S Wagner, Thomas A. Horbett, David G. CastnerAbstract:Characterization of complex Adsorbed Protein films is a critical aspect of biomaterials science, particularly in understanding the in vivo response to biomaterials. The surface analysis techniques electron spectroscopy for chemical analysis (ESCA) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) are particularly suited to the analysis of complex Adsorbed Protein films due to their wide applicability to a variety of materials. We have investigated the applicability of ESCA for studying the structure of Adsorbed serum and plasma Protein layers. ESCA was able to monitor the thickness of the Adsorbed Protein film. Due to its chemical specificity, ToF-SIMS was used to estimate the composition of the plasma and serum Protein layers by comparison of their spectra with the spectra of single Protein films. The limit of detection of ToF-SIMS for the plasma Protein fibrinogen was determined by comparison with independent radiolabeled fibrinogen adsorption measurements. While ToF-SIMS was able to determine some qualitative trends in the composition of the plasma Protein films as a function of adsorption time, the detection limit of the minor components in multicomponent Adsorbed Protein films ultimately limits the ability of ToF-SIMS to quantify the composition of these films. However, both ESCA and ToF-SIMS can provide useful information on Adsorbed plasma Protein films without further sample treatment. This study outlines the strengths and weaknesses of ESCA and ToF-SIMS for studying multicomponent Adsorbed plasma Protein films.
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characterization of Adsorbed Protein films using time of flight secondary ion mass spectrometry and multivariate analysis
Applied Surface Science, 2003Co-Authors: M S Wagner, David G. CastnerAbstract:The complexity of the mass spectra obtained by static time-of-flight-secondary ion mass spectrometry (ToF-SIMS) demands high-throughput data analysis techniques that rapidly process and interpret the resulting data. We have used ToF-SIMS to analyze Adsorbed Protein films. Positive ion mass spectra from different Protein films are challenging to differentiate due to the absence of unique, identifying peaks between the different spectra. Therefore, the multivariate pattern recognition techniques principal component analysis (PCA) and linear discriminant analysis (LDA) have been employed to differentiate the spectra of different Proteins and understand the major sources of variation in these spectra. Because of its supervised nature, LDA enhanced discrimination between groups and classification of unknowns when compared with PCA. However, PCA was able to provide better information on the sources of variation in the data set. Both PCA and LDA are important in the analysis of static ToF-SIMS spectra from organic samples.
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classification of Adsorbed Protein static tof sims spectra by principal component analysis and neural networks
Surface and Interface Analysis, 2002Co-Authors: O D Sanni, David G. Castner, M S Wagner, D Briggs, J C VickermanAbstract:Analysis of the static time-of-flight secondary ion mass spectrometry (ToF-SIMS) spectra of Adsorbed Protein films is reported using principal component analysis (PCA) and a novel artificial neural network (ANN) approach, NeuroSpectraNet, to classify chemically the spectra of the Protein films. The ease of application and the efficiency with which each approach classified positive ion spectra from Adsorbed films of 13 different Proteins is reported and assessed. The ToF-SIMS spectra of Adsorbed Protein films are especially difficult to analyze owing to the absence of unique peaks in the spectra of different Proteins. Although PCA was able to differentiate successfully ToF-SIMS spectra of Adsorbed Protein films using the ions generated from the fragmentation of the amino acids, differentiation of the spectra using the entire spectrum was unsuccessful. Outliers in several of the Protein groups make classification of unknown spectra difficult, despite the use of only amino-acid-specific ions. However, NeuroSpectraNet successfully classified the spectra from 11 of the Protein films using the whole positive ion spectra after a vector analysis enhancement had been incorporated into the neural network. Full classification of all 13 Proteins was achieved by using the combined positive and negative ion spectra. However, as with PCA, ANN classification was enhanced when the input patterns only contained amino-acid-specific ions. The complex and multivariate nature of static SIMS spectra is a domain well suited to the application of neural networks for pattern recognition and classification. Copyright © 2002 John Wiley & Sons, Ltd.
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interpretation of static time of flight secondary ion mass spectra of Adsorbed Protein films by multivariate pattern recognition
Analytical Chemistry, 2002Co-Authors: M S Wagner, Bonnie J Tyler, David G. CastnerAbstract:Multivariate analysis has become increasingly common in the analysis of multidimensional spectral data. We previously showed that the multivariate analysis technique principal component analysis (PCA) is an excellent method for interpreting the static time-of-flight secondary ion mass spectrometry (TOF-SIMS) spectra of Adsorbed Protein films. PCA is an unsupervised pattern recognition technique that loses resolution between spectra of different Proteins as more Proteins are added to the data set due to large within-group variation. The supervised pattern recognition techniques discriminant principal component analysis (DPCA) and linear discriminant analysis (LDA), which aim to control within-group variation while maximizing between-group separation to enhance discrimination between groups, were compared with PCA using data sets of TOF-SIMS spectra of Proteins Adsorbed onto mica and PTFE substrates. DPCA and LDA quantitatively improved discrimination between groups and provided different information about the data than PCA. LDA was able to classify unknown samples with a misclassification rate lower than PCA or DPCA. Both unsupervised and supervised pattern recognition techniques are useful for the interpretation and classification of static TOF-SIMS spectra of Adsorbed Protein films.
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interpretation of static time of flight secondary ion mass spectra of Adsorbed Protein films by multivariate pattern recognition
Analytical Chemistry, 2002Co-Authors: M S Wagner, Bonnie J Tyler, David G. CastnerAbstract:Multivariate analysis has become increasingly common in the analysis of multidimensional spectral data. We previously showed that the multivariate analysis technique principal component analysis (PCA) is an excellent method for interpreting the static time-of-flight secondary ion mass spectrometry (TOF-SIMS) spectra of Adsorbed Protein films. PCA is an unsupervised pattern recognition technique that loses resolution between spectra of different Proteins as more Proteins are added to the data set due to large within-group variation. The supervised pattern recognition techniques discriminant principal component analysis (DPCA) and linear discriminant analysis (LDA), which aim to control within-group variation while maximizing between-group separation to enhance discrimination between groups, were compared with PCA using data sets of TOF-SIMS spectra of Proteins Adsorbed onto mica and PTFE substrates. DPCA and LDA quantitatively improved discrimination between groups and provided different information about ...
Thomas A. Horbett - One of the best experts on this subject based on the ideXlab platform.
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characterizing multicomponent Adsorbed Protein films using electron spectroscopy for chemical analysis time of flight secondary ion mass spectrometry and radiolabeling capabilities and limitations
Biomaterials, 2003Co-Authors: M S Wagner, Thomas A. Horbett, David G. CastnerAbstract:Characterization of complex Adsorbed Protein films is a critical aspect of biomaterials science, particularly in understanding the in vivo response to biomaterials. The surface analysis techniques electron spectroscopy for chemical analysis (ESCA) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) are particularly suited to the analysis of complex Adsorbed Protein films due to their wide applicability to a variety of materials. We have investigated the applicability of ESCA for studying the structure of Adsorbed serum and plasma Protein layers. ESCA was able to monitor the thickness of the Adsorbed Protein film. Due to its chemical specificity, ToF-SIMS was used to estimate the composition of the plasma and serum Protein layers by comparison of their spectra with the spectra of single Protein films. The limit of detection of ToF-SIMS for the plasma Protein fibrinogen was determined by comparison with independent radiolabeled fibrinogen adsorption measurements. While ToF-SIMS was able to determine some qualitative trends in the composition of the plasma Protein films as a function of adsorption time, the detection limit of the minor components in multicomponent Adsorbed Protein films ultimately limits the ability of ToF-SIMS to quantify the composition of these films. However, both ESCA and ToF-SIMS can provide useful information on Adsorbed plasma Protein films without further sample treatment. This study outlines the strengths and weaknesses of ESCA and ToF-SIMS for studying multicomponent Adsorbed plasma Protein films.
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quantitative time of flight secondary ion mass spectrometry for the characterization of multicomponent Adsorbed Protein films
Applied Surface Science, 2003Co-Authors: Matthew Scott Wagner, Thomas A. Horbett, Mingchao Shen, David G. CastnerAbstract:Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is ideal for the characterization of Adsorbed Proteins due to its chemical specificity and surface sensitivity. We have employed ToF-SIMS and multivariate analysis to determine the surface composition of Adsorbed Protein films from binary mixtures, blood serum, and blood plasma. Good correlation between ToF-SIMS data and independent radiolabeling studies was achieved for binary mixtures, though these results depended on the substrate. Qualitative insight into the composition of the serum and plasma Protein films was obtained via comparison to standard single Protein film spectra. ToF-SIMS and multivariate analysis were able to measure the surface composition of multicomponent Adsorbed Protein films.
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Characterization of the structure of binary and ternary Adsorbed Protein films using electron spectroscopy for chemical analysis, time-of-flight secondary ion mass spectrometry, and radiolabeling
Langmuir, 2003Co-Authors: Matthew Scott Wagner, Thomas A. Horbett, David G. CastnerAbstract:In complex Adsorbed Protein films, the biological reactivity of the Adsorbed Proteins depends on their relative concentrations, organization, conformation, and orientation. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) samples the outermost composition of an Adsorbed Protein film, providing biologically relevant information about the organization and availability of the Adsorbed Proteins in the film. We have previously shown that ToF-SIMS can quantitatively measure the composition of binary Adsorbed Protein films. However, for one particular binary system studied (immunoglobulin G−fibrinogen), a difference between the ToF-SIMS and 125I-radiolabeled Protein adsorption measurements was reported. It was hypothesized that the composition of the Protein film at its outermost (and, therefore, most biologically relevant) surface was different than that of the overall Protein film due to the protrusion of the Adsorbed fibrinogen over the Adsorbed immunoglobulin G. This study provides further evidence ...
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quantitative analysis of binary Adsorbed Protein films by time of flight secondary ion mass spectrometry
Journal of Biomedical Materials Research Part A, 2003Co-Authors: Matthew Scott Wagner, Thomas A. Horbett, Mingchao Shen, David G. CastnerAbstract:Time of flight secondary ion mass spectrometry (ToF-SIMS) is an ideal technique for the analysis of Adsorbed Protein films because of its surface sensitivity and chemical specificity. In this study, we examined ToF-SIMS with the multivariate calibration method partial least squares regression (PLSR) for the determination of the relative abundance of the components in binary Protein films Adsorbed onto mica, PTFE, and heptyl amine plasma polymer substrates. These results have been compared with independently measured 125I-radiolabeled Protein adsorption experiments. By applying PLSR to the ToF-SIMS data, the relative abundance of the components in the binary Adsorbed Protein films was quantified, and the agreement between the ToF-SIMS and 125I-radiolabeling data was measured by the root mean square prediction error (RMSPE). Differences in Protein quantification by PLSR and 125I-radiolabeling ranged from 5 to 25 mass % RMSPE and were highly dependent on the structure of the Adsorbed Protein film, the substrate surface chemistry and morphology, and the number of latent variables retained in the PLSR model. The limit of detection for the minor component in the Adsorbed Protein film was found to be approximately 10 mass %. This study demonstrates that the combination of ToF-SIMS and multivariate calibration provide complementary information to 125I-radiolabeling about the composition and structure of binary Adsorbed Protein films. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res 64A: 1–11, 2003
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limits of detection for time of flight secondary ion mass spectrometry tof sims and x ray photoelectron spectroscopy xps detection of low amounts of Adsorbed Protein
Journal of Biomaterials Science-polymer Edition, 2002Co-Authors: M S Wagner, Thomas A. Horbett, Mingchao Shen, Sally L Mcarthur, David G. CastnerAbstract:Characterization of biomaterial surfaces requires analytical techniques that are capable of detecting a wide concentration range of Adsorbed Protein. This range includes detection of low amounts of Adsorbed Protein (<10 ng/cm2) that may be present on non-fouling biomaterials. X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) are surface sensitive techniques capable of detecting Adsorbed Proteins. We have investigated the lower limits of detection of both XPS and ToF-SIMS on four model substrates each presenting unique challenges for analysis by XPS and ToF-SIMS: mica, poly(tetrafluoroethylene), allyl amine plasma polymer and heptyl amine plasma polymer. The detection limit for XPS ranged from 10 ng/cm2 of fibrinogen (on mica) to 200 ng/cm2 (on allyl amine plasma polymers). The detection limit for ToF-SIMS ranged from 0.1 ng/cm2 of fibrinogen to 100 ng/cm2, depending on the substrate and data analysis. Optimal conditions provided detection limits between 0.1 ng/cm2 and 15 ng/cm2 on all of the substrates used in this study. While both techniques were shown to be effective in detecting Protein, the sensitivity of both XPS and ToF-SIMS was shown to be dependent on substrate surface chemistry and the organization of the Adsorbed Protein film. This study specifically highlights the applicability of ToF-SIMS in the characterization of low level Protein adsorption.
Matthew Scott Wagner - One of the best experts on this subject based on the ideXlab platform.
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quantitative time of flight secondary ion mass spectrometry for the characterization of multicomponent Adsorbed Protein films
Applied Surface Science, 2003Co-Authors: Matthew Scott Wagner, Thomas A. Horbett, Mingchao Shen, David G. CastnerAbstract:Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is ideal for the characterization of Adsorbed Proteins due to its chemical specificity and surface sensitivity. We have employed ToF-SIMS and multivariate analysis to determine the surface composition of Adsorbed Protein films from binary mixtures, blood serum, and blood plasma. Good correlation between ToF-SIMS data and independent radiolabeling studies was achieved for binary mixtures, though these results depended on the substrate. Qualitative insight into the composition of the serum and plasma Protein films was obtained via comparison to standard single Protein film spectra. ToF-SIMS and multivariate analysis were able to measure the surface composition of multicomponent Adsorbed Protein films.
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Characterization of the structure of binary and ternary Adsorbed Protein films using electron spectroscopy for chemical analysis, time-of-flight secondary ion mass spectrometry, and radiolabeling
Langmuir, 2003Co-Authors: Matthew Scott Wagner, Thomas A. Horbett, David G. CastnerAbstract:In complex Adsorbed Protein films, the biological reactivity of the Adsorbed Proteins depends on their relative concentrations, organization, conformation, and orientation. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) samples the outermost composition of an Adsorbed Protein film, providing biologically relevant information about the organization and availability of the Adsorbed Proteins in the film. We have previously shown that ToF-SIMS can quantitatively measure the composition of binary Adsorbed Protein films. However, for one particular binary system studied (immunoglobulin G−fibrinogen), a difference between the ToF-SIMS and 125I-radiolabeled Protein adsorption measurements was reported. It was hypothesized that the composition of the Protein film at its outermost (and, therefore, most biologically relevant) surface was different than that of the overall Protein film due to the protrusion of the Adsorbed fibrinogen over the Adsorbed immunoglobulin G. This study provides further evidence ...
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quantitative analysis of binary Adsorbed Protein films by time of flight secondary ion mass spectrometry
Journal of Biomedical Materials Research Part A, 2003Co-Authors: Matthew Scott Wagner, Thomas A. Horbett, Mingchao Shen, David G. CastnerAbstract:Time of flight secondary ion mass spectrometry (ToF-SIMS) is an ideal technique for the analysis of Adsorbed Protein films because of its surface sensitivity and chemical specificity. In this study, we examined ToF-SIMS with the multivariate calibration method partial least squares regression (PLSR) for the determination of the relative abundance of the components in binary Protein films Adsorbed onto mica, PTFE, and heptyl amine plasma polymer substrates. These results have been compared with independently measured 125I-radiolabeled Protein adsorption experiments. By applying PLSR to the ToF-SIMS data, the relative abundance of the components in the binary Adsorbed Protein films was quantified, and the agreement between the ToF-SIMS and 125I-radiolabeling data was measured by the root mean square prediction error (RMSPE). Differences in Protein quantification by PLSR and 125I-radiolabeling ranged from 5 to 25 mass % RMSPE and were highly dependent on the structure of the Adsorbed Protein film, the substrate surface chemistry and morphology, and the number of latent variables retained in the PLSR model. The limit of detection for the minor component in the Adsorbed Protein film was found to be approximately 10 mass %. This study demonstrates that the combination of ToF-SIMS and multivariate calibration provide complementary information to 125I-radiolabeling about the composition and structure of binary Adsorbed Protein films. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res 64A: 1–11, 2003
Eric Dickinson - One of the best experts on this subject based on the ideXlab platform.
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food colloids research historical perspective and outlook
Advances in Colloid and Interface Science, 2011Co-Authors: Eric DickinsonAbstract:Abstract Trends and past achievements in the field of food colloids are reviewed. Specific mention is made of advances in knowledge and understanding in the areas of (i) structure and rheology of Protein gels, (ii) properties of Adsorbed Protein layers, (iii) functionality derived from Protein–polysaccharide interactions, and (iv) oral processing of food colloids. Amongst ongoing experimental developments, the technique of particle tracking for monitoring local dynamics and microrheology of food colloids is highlighted. The future outlook offers exciting challenges with expected continued growth in research into digestion processes, encapsulation, controlled delivery, and nanoscience.
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depletion flocculation of caseinate stabilised emulsions what is the optimum size of the non Adsorbed Protein nano particles
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2004Co-Authors: Stewart J Radford, Eric DickinsonAbstract:We address the issue of the size of the Protein aggregates (nano-particles) required to produce depletion flocculation in sodium caseinate-stabilised emulsions of neutral pH. We predict that a casein nano-particle radius of around 20 nm causes the strongest depletion flocculation of fine emulsion droplets (mean diameter ∼0.4 μm), i.e., corresponding to a size ratio of about 10:1. This optimum size is the result of a compromise between (i) it being small enough to generate a high number density of non-Adsorbed nano-particles, and hence a substantial osmotic pressure, and (ii) it being large enough to give a substantial depletion layer thickness. It turns out that the estimated optimum size of casein nano-particles for inducing depletion flocculation is similar to the size of small casein aggregates actually found in sodium caseinate dispersions at low ionic strength.
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Adsorbed Protein layers at fluid interfaces interactions structure and surface rheology
Colloids and Surfaces B: Biointerfaces, 1999Co-Authors: Eric DickinsonAbstract:Abstract Properties of Adsorbed layers of Proteins at air–water and oil–water interfaces are reviewed. Emphasis is placed on recent developments in understanding the adsorption and surface rheology of individual globular Proteins, especially the milk Protein β-lactoglobulin, in the absence and presence of other Proteins or small-molecule surfactants. Problems of modelling Adsorbed layer structure and surface equation of state against a background of irreversibility and molecular complexity are addressed. Similarities and differences are described between impenetrable solid and mobile fluid surfaces, between air–water and oil–water interfaces, between shear and dilatational surface deformations, and between globular Proteins and disordered Proteins (caseins). A new simulation model is discussed in which the Adsorbed globular Protein monolayer is modelled mesoscopically as a flexible bonded network of spherical particles. The model can describe various characteristic properties of viscoelastic gel-like Protein layers, including time-dependent changes in properties arising as a result of large-scale dilatational deformations. Competitive displacement of β-lactoglobulin from the air–water interface by non-ionic surfactant has been demonstrated directly by neutron reflectivity. While some good correlations have now been established between properties of mixed Protein+surfactant layers and the stability of foam and emulsion systems, the detailed relationship between surface rheology and colloid stability is still poorly understood.
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simulation of interfacial shear and dilatational rheology of an Adsorbed Protein monolayer modeled as a network of spherical particles
Langmuir, 1998Co-Authors: Christopher M Wijmans, Eric DickinsonAbstract:We have studied the small-deformation rheology of a (semi-) two-dimensional model network of spherical particles, representing an Adsorbed monolayer of Protein at a fluid−fluid interface. The parti...
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faraday research article structure and composition of Adsorbed Protein layers and the relationship to emulsion stability
Journal of the Chemical Society Faraday Transactions, 1992Co-Authors: Eric DickinsonAbstract:Factors affecting the stability of oil-in-water emulsions with respect to coalescence, creaming and flocculation are critically reviewed with emphasis on the role of Adsorbed Protein and free polysaccharide. Crucial differences in structure between Adsorbed layers of a disordered Protein (β-casein) and a globular Protein are described with particular reference to recent results obtained by specular neutron reflectance. Based on parallel experiments in emulsions and at planar oil/water interfaces, information is now becoming available on the structure and composition of layers Adsorbed from mixtures of Proteins or mixtures of Protein + surfactant. Some of the general features of competitive and cooperative adsorption in mixed systems containing Protein can be described by a new lattice-based Monte Carlo computer simulation model. In this regard, the statistical description of how covalent linkage to polysaccharide affects the surface and emulsifying behaviour of Protein is especially noteworthy.