Measurement of length distribution of beta-lactoglobulin fibrils by multiwavelength analytical ultracentrifugation

The whey protein beta-lactoglobulin is the building block of amyloid fibrils which exhibit a great potential in various applications. These include stabilization of gels or emulsions. During biotechnological processing, high shear forces lead to fragmentation of fibrils and therefore to smaller fibril lengths. To provide insight into such processes, pure straight amyloid fibril dispersions (prepared at pH 2) were produced and sheared using the rotor stator setup of an Ultra Turrax. In the first part of this work, the sedimentation properties of fragmented amyloid fibrils sheared at different stress levels were analyzed with mulitwavelength analytical ultracentrifugation (AUC). Sedimentation data analysis was carried out with the boundary condition that fragmented fibrils were of cylindrical shape, for which frictional properties are known. These results were compared with complementary atomic force microscopy (AFM) measurements. We demonstrate how the sedimentation coefficient distribution from AUC experiments is influenced by the underlying length and diameter distribution of amyloid fibrils. In the second part of this work, we show how to correlate the fibril size reduction kinetics with the applied rotor revolution and the resulting energy density, respectively, using modal values of the sedimentation coefficients obtained from AUC. Remarkably, the determined scaling laws for the size reduction are in agreement with the results for other material systems, such as emulsification processes or the size reduction of graphene oxide sheets.</p

The Stokes-Einstein-Sutherland equation at the nanoscale revisited

The Stokes-Einstein-Sutherland (SES) equation is at the foundation of statistical physics, relating a particle's diffusion coefficient and size with the fluid viscosity, temperature and the boundary condition for the particle-solvent interface. It is assumed that it relies on the separation of scales between the particle and the solvent, hence it is expected to break down for diffusive transport on the molecular scale. However, a number of experimental studies showed a remarkable small, if any, violation of this equation down to the size of a nm, where there is no scale separation. To resolve this puzzle we combine analytical ultracentrifugation experiments and molecular dynamics simulations to study the transport of buckminsterfullerene C$_{60}$ suspended in toluene at infinite dilution. We show that this system clearly violates the conditions of slow momentum relaxation. Yet, through a linear response to a constant force, we show both in experiments and in simulations that the SES equation can be recovered in the long time limit with no more than 4% uncertainty. This nonetheless requires partial slip on the particle interface, extracted consistently from all the data. Our results, thus, resolve a long-standing discussion on the validity and limits of the SES equation at the molecular scale

A multiwavelength emission detector for analytical ultracentrifugation

In this study, a new detector for multiwavelength emission analytical ultracentrifugation (MWE-AUC) is presented, which allows measuring size- or composition-dependent fluorescence properties of nanoparticle ensembles. Validation of the new setup is carried out via comparison to a benchtop photoluminescence spectrometer and the established extinction-based multiwavelength analytical ultracentrifuge (MWL-AUC). The results on fluorescent proteins and silica particles demonstrate that the new device not only correctly reproduces sedimentation and diffusion coefficients of the particles but provides also meaningful fluorescence spectra. As an application example for a sample exhibiting a broad particle size distribution, spectra and size of graphene oxide nanoplatelets are extracted simultaneously. Narrowly distributed CdSe/ZnS quantum dots showing size- and structure-dependent shifts of their fluorescence spectra are analyzed as well. The combination of MWE- and MWL-AUC provides a comprehensive framework for the optical characterization for nanoparticles and macromolecules in terms of their extinction and emission properties

Development of an advanced multiwavelength emission detector for the analytical ultracentrifuge

&lt;p&gt;This is the raw data for the manuscript:&lt;/p&gt; &lt;p&gt;Development of an advanced multiwavelength emission detector for the analytical ultracentrifuge.&lt;/p&gt; &lt;p&gt;A readme file containing all descriptions can be found in the main folder. All data are sorted according to their appearance in the figures of the main manuscript and electronic supplementary information.&lt;/p&gt; &lt;p&gt;Abstract:&lt;/p&gt; &lt;p&gt;An advanced design of the analytical ultracentrifuge (AUC) with multiwavelength emission detection (MWE-AUC) is presented which offers outstanding performance concerning the spectral resolution and range flexibility as well as the quality of the data acquired. The excitation by a 520 nm laser is complemented with a 405 nm laser. An external spectrograph with three switchable tunable gratings permits optimisation of the spectral resolution in an order of magnitude range while keeping the spectral region broad. The new system design leads also to a significant reduction of systematic signal noise and allows the assessment and control of inner filter effects. Details regarding the very large signal dynamic range are presented, an important aspect when studying samples in a broad concentration range of up to five orders of magnitude. Custom-made mono-sector sample cells with 3 mm titanium centerpiece have been developed and are applied as default system components. Our system is validated by complementary studies on two biological systems, fluorescent bovine serum albumin and green fluorescent protein, using the commercial Optima AUC with absorbance detection for comparison. Finally, we demonstrate the capabilities of our second generation MWE-AUC with respect to multiwavelength characterisation of gold nanoclusters, which exhibit specific fluorescence depending on their structure. Overall, this work depicts an important step-stone for the future in-depth studies of size-, shape- and composition-dependent multiwavelength emission properties of colloids.&lt;/p&gt

Multidimensional Fractionation of Particles

The increasing complexity in particle science and technology requires the ability to deal with multidimensional property distributions. We present the theoretical background for multidimensional fractionations by transferring the concepts known from one dimensional to higher dimensional separations. Particles in fluids are separated by acting forces or velocities, which are commonly induces by external fields, e.g., gravitational, centrifugal or electro-magnetic fields. In addition, short-range force fields induced by particle interactions can be employed for fractionation. In this special case, nanoparticle chromatography is a recent example. The framework for handling and characterizing multidimensional separation processes acting on multidimensional particle size distributions is presented. Illustrative examples for technical realizations are given for shape-selective separation in a hydrocyclone and for density-selective separation in a disc separator