Aggregation of Aβ Alzheimer's disease‐related peptide studied by dynamic light scattering
Markus ThuneckeAlessandro LobbiaUlrich KosciessaThomas DyrksAE OakleyJonathan D. TurnerWolfram SaengerYannis Georgalis
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The aggregation behavior of the major component of Alzheimer's disease-related, amyloid peptides, Abeta-(1-40) and Abeta-(1-42), was studied in solution using dynamic light scattering. With most solvents employed, we found fibrils coexisting with oligomeric Abeta species. Pronounced differences were observed in aggregation of Abeta-(1-40) and (1-42) sequences in acetonitrile-water mixtures. Cofactors such as Zn2+ were found to induce deaggregation of Abeta instead of aggregation. The results indicated that the initial state of the peptide immediately after synthesis is rather poorly defined. Using freezing instead of lyophilization after the final peptide synthesis step, may partially relieve these problems.List of contributors 1. Dynamic scattering from multicomponent polymer mixtures in solution and in bulk 2. Single photon correlation techniques 3. Noise on photon correlation functions and its effects on data reduction algorithms 4. Data analysis in dynamic light scattering 5. Dynamic light scattering and linear viscoelasticity of polymers in solution and in the bulk 6. Dynamic properties of polymer solutions 7. Application of dynamic light scattering to polyelectrolytes in solution 8. Simultaneous static and dynamic light scattering: application to polymer structure analysis 9. Dynamic light scattering from dense polymer systems 10. Dynamic light scattering from polymers in solution and in bulk 11. Dynamic light scattering from polymer gels 12. Dynamic light scattering from rigid and nearly rigid rods 13. Light scattering in micellar systems 14. Critical dynamics of binary liquid mixtures and simple fluids studied using dynamic light scattering 15. Application of dynamic light scattering to biological systems 16. Diffusing-wave spectroscopy Index
Electrophoretic light scattering
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Colloidal systems are a subject of great interest in soft condensed matter research as well as in industry. But the ability to characterize colloidal systems with dynamic light scattering (DLS) is in general limited to systems with negligible contributions from multiple scattering of light. Therefore a variety of systems is excluded from investigations with DLS at high concentration and therefore increased turbidity. Often these samples were investigated under high dilution with, at least for some systems, a high probability of measuring artefacts. A promising solution to this problem consists of suppressing multiple scattering in a DLS experiment with a cross-correlation technique. Therefore we developed a so-called 3d cross-correlation instrument which enables us to characterize extremely turbid suspensions. After having found that the instrument works very well with model systems, we now demonstrate that complex ‘real world’ systems can successfully be characterized using this technique. An investigation of milk shows a strong dependence of the measured particle size distribution upon dilution. With the 3d instrument, however, the undiluted milk can be measured and artificial changes of the sample properties can be excluded.
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This chapter provides a more detailed background to dynamic light scattering (DLS), starting with static light scattering (SLS), as the tools derived can be valuable for the subsequent derivation of the relevant electric field and intensity autocorrelation functions. The theoretical background is followed by a more detailed discussion of particle sizing and the evaluation of size distributions. The main section on DLS is followed by a description of new instrumental approaches to DLS based mainly on fibre optics, which allow DLS measurements to be made in more difficult environments. The chapter concludes with the introduction of a very new video-microscopy technique, namely differential dynamic microscopy (DDM). The two main applications of DLS in chemistry are particle sizing and the study of molecular aggregation and growth. A section discusses several practical examples, with particular focus on nanocolloids for their relevance in catalysis and self-assembled systems such as surfactants and block copolymers.
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Modeling light propagation in the whole body is essential and necessary for optical imaging. However, non-scattering, low-scattering and high absorption regions commonly exist in biological tissues, which lead to inaccuracy of the existing light transport models. In this paper, a novel hybrid light transport model that couples the simplified spherical harmonics approximation (SPN) with the radiosity theory (HSRM) was presented, to accurately describe light transport in turbid media with non-scattering, low-scattering and high absorption heterogeneities. In the model, the radiosity theory was used to characterize the light transport in non-scattering regions and the SPN was employed to handle the scattering problems, including subsets of low-scattering and high absorption. A Neumann source constructed by the light transport in the non-scattering region and formed at the interface between the non-scattering and scattering regions was superposed into the original light source, to couple the SPN with the radiosity theory. The accuracy and effectiveness of the HSRM was first verified with both regular and digital mouse model based simulations and a physical phantom based experiment. The feasibility and applicability of the HSRM was then investigated by a broad range of optical properties. Lastly, the influence of depth of the light source on the model was also discussed. Primary results showed that the proposed model provided high performance for light transport in turbid media with non-scattering, low-scattering and high absorption heterogeneities.
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A unified theory for light scattering by biological cells is presented. It is shown that Mie scattering from the bare cell and
the nucleus dominates cell light scattering in the forward directions. The random fluctuation of the background refractive
index within the cell, behaving as a fractal random continuous medium, dominates light scattering by cells in other angles.
The theory is validated by experimental angular light scattering spectra of epithelial cells for scattering angles from 1.25
to 173.8 degrees and in the spectral range from 400nm to 700nm.
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Dynamic light scattering (DLS) has proven as a successful technique both for the determination of various thermophysical properties of fluids [1][2] and for particle size analysis [3][4]. A useful special application of characterising fluids by DLS is the measurement of the dynamic viscosity [5][6].
Static light scattering
Electrophoretic light scattering
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This study represents the first attempts at a systematic study of light scattering in polycrystalline materials both in the visible and infra-red region where all parameters responsible for scattering are independently varied. Light is scattered by voids and second phase particles. Light is also reflected and refracted by grain interfaces of random crystal orientations. With sufficient optical density of the sample, multiple scattering from voids, grain boundaries or second phase particles becomes the significant scattering mechanism in polycrystalline material. The diffuse scattering envelope width is measured and various scattering mechanisms are identified with respect to the way they influence this scattering width. Existing theories are reviewed and it is shown how these theories can qualitatively account for the observed behavior.
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In biological suspensions light is scattered by the suspended cells. When the concentration of the scattering centers increases multiple scattering becomes dominant. A main challenge in modeling light diffusion is to find an analytical expression that describes the multiple light scattering in an accurate manner, including light scattering anisotropy. The Henyey-Greenstein phase function embedded in the RWMCS code previously written was used to describe single scattering on Red Blood Cells in suspension. The results of the simulation, containing multiple light scattering, are used to verify the predictions of two effective phase functions. Previous published results revealed a good agreement with experimental data in the small concentration range for scattering centers having a diameter of several microns. The new simulation expanded the investigation in the bigger optical depth targets and the results are presented in the extended paper.
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Abstract Dynamic light scattering is a new method for investigating macromolecular systems. The importance of the technique lies in its non-invasive character. It can be employed on extremely small fluid volumes, the instrumentation is relatively inexpensive and allows the rapid determination of diffusion coefficients as well as providing information on relaxation time distributions for the macromolecular components of complex systems. This volume is directed in part to the philosophy and current practice in dynamic light scattering: single photon correlation techniques are introduced, a discussion of noise on photon correlation functions is given and data analysis in dynamic light scattering to polymer structure analysis is presented and a comprehensive introduction to diffusing wave spectroscopy is given. Theoretical developments relating dynamic light scattering to the viscoelasticity of polymers in solution and in the bulk are described. The second aim is to illustrate the widely varying fields in which the technique finds application. Chapters are to be found on multicomponent mixtures, polyelectrolytes, dense polymer systems, gels, rigid rods, micellar systems and the application of dynamic light scattering to biological systems.
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The ability to characterize colloidal suspensions by means of dynamic light scattering is limited to systems with negligible contributions from multiple scattering. For larger particle sizes with high scattering contrast this immediately limits the technique to very low concentrations. A very interesting solution of this problem is to suppress multiple scattering in dynamic light scattering experiments using various cross-correlation schemes. Based on these considerations we have constructed a so-called 3D cross-correlation experiment with which we are able to characterize extremely turbid suspensions. We have tested the feasibility of these experiments with well defined model systems such as suspensions of monodisperse and bimodal latex particles with relatively high volume fractions. The results are very promising and demonstrate unambiguously that such systems can be quantitatively characterized by means of dynamic light scattering methods without having to resort to high dilution.
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Electrophoretic light scattering
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