Dynamic Light Scattering Setup Research Articles

Profiling Particles of Sahara Dust Settled on the Ground by a Simplified Dynamic Light Scattering Procedure and Sedimentation.

Dust particles exist in the form of mineral aerosols and play a significant role in climate change patterns, while also having the potential to affect human health. The size of these particles is crucial, as it determines the atmosphere's albedo. In the past few years, a Saharan dust cloud has moved and arrived above Romania during spring, followed by rain containing the dust particles, which are deposited on various objects. We collected these particles in an aqueous suspension and employed natural sedimentation to separate them by density. We then conducted a dynamic light scattering (DLS) experiment to analyze their size. Our DLS setup was straightforward, and the time series analysis involved evaluating the frequency spectrum of the scattered light intensity-also known as the power spectrum-filtering it, and fitting the expected Lorentzian line to it to determine the parameters and the average diameter of the suspended particles. We found that the dust particles had a continuous distribution, with the biggest particles having a diameter around 1100 nm. The results obtained from the combination of sedimentation and DLS are consistent with reports on the size of Saharan dust particles in other regions of Europe.

Multi-angle in situ dynamic light scattering at a neutron spin echo spectrometer.

A new sample environment, called Bio-Oven, has been built for the Neutron Spin Echo (NSE) Spectrometer J-NSE Phoenix. It provides active temperature control and the possibility to perform Dynamic Light Scattering (DLS) measurements during the neutron measurement. DLS provides diffusion coefficients of the dissolved nanoparticles, and thus one can monitor the aggregation state of the sample on a time scale of minutes during the spin echo measurement times on the order of days. This approach helps to validate the NSE data or to replace the sample when its aggregation state influences the spin echo measurement results. The new Bio-Oven is an in situ DLS setup based on optical fibers decoupling the free space optics around the sample cuvette in a lightproof casing from the laser sources and the detectors. It collects light from three scattering angles simultaneously. Six different values of momentum transfer can be accessed by switching between two different laser colors. Test experiments were performed with silica nanoparticles with diameters ranging from 20nm up to 300nm. Their hydrodynamic radii were determined from DLS measurements and compared with the ones obtained by a commercial particle sizer. It was demonstrated that also the static light scattering signal can be processed and gives meaningful results. The protein sample apomyoglobin was used for a long-term test and in a first neutron measurement using the new Bio-Oven. The results prove that the aggregation state of the sample can be followed using in situ DLS along with the neutron measurement.

Investigation into the Size Distribution of Al<sub>2</sub>O<sub>3</sub>- ZnO Nanoparticles Dispersed in DI Water and Following the Impact of CNTs on the Stability, Heat Transfer, and Electricity Transfer of Al<sub>2</sub>O<sub>3</sub>- ZnO-CNT Hybrid Nanofluid

The stability of dispersed nanoparticles in the base fluid has always been one of the most important challenges in using nanofluids as a coolant in heat transfer applications in different industries such as modern electronic equipment, heat exchangers, solar technologies, etc. In the present study, the dynamic light scattering (DLS) method is used to obtain the particle size distribution of Al2O3-ZnO dispersed in DI water. After adjusting the optical arrangement and designing the DLS setup, the correlation curves are plotted by analyzing the detected signals of the experiments. Then, a decay rate is derived by fitting an exponential function to the correlation curve to get the particle size distribution by using the Stoke-Einstein equation. In order to investigate the stability of Al2O3-ZnO water-based nanofluid, the particle size distribution profiles are studied several times. In addition, the stability of Al2O3-ZnO-CNT hybrid nanofluid is followed by absorbance measurements using a UV-Vis spectrophotometer. Moreover, the thermal conductivity coefficient and electrical conductivity of the Al2O3-ZnO hybrid nanofluid with and without CNT particles are determined by utilizing KD2 Pro and PCT-407 devices, respectively. The results showed that the peak in the particle size distribution curve for Al2O3-ZnO hybrid nanofluid shifted from 476 nm to 128 nm after 5 days. Furthermore, the inclusion of carbon nanotubes increased the stability of zinc oxide particles in the nanofluid. In addition, by adding carbon nanotubes in a ratio of 1:1:0.5 to Al2O3-ZnO nanofluid and forming 0.05 wt.% hybrid nanofluid, the thermal conductivity coefficient was enhanced by 30% in comparison with deionized water, while a 0.05 wt.% hybrid nanofluid without CNT particles improved the thermal conductivity by 19%. Although the electrical conductivity increased by adding nanoparticles to the base fluid, it didn’t change significantly for nanofluids containing CNTs compared to nanofluids without CNT particles.

Determination of thermal and mutual diffusivity of n-heptane with dissolved carbon dioxide by dynamic light scattering

In this work, thermal and mutual diffusivity of n-heptane (n-C7H16) with dissolved carbon dioxide (CO2) were simultaneously measured using dynamic light scattering (DLS) method from 298 to 473 K and saturation pressure up to 5.5 MPa. For this purpose, the DLS setup as well as temperature and pressure system were improved. Two hydrodynamic modes in connection with the statistical fluctuations of entropy and species were verified. The average expanded uncertainty of thermal and mutual diffusivity were 9.0% and 4.9% with a coverage factor of k = 2. The thermal and mutual diffusivity versus pressure under isothermal lines were briefly discussed and a comparison with literature was performed. The experimental thermal and mutual diffusivity measured in this work are in reasonable agreement with the literature data. This work is expected to provide fundamental data for engineering process.

DLS Setup for in Situ Measurements of Photoinduced Size Changes of Microgel-Based Hybrid Particles.

Photoinduced size changes in microgel particles loaded with gold nanoparticles (AuNPs) were investigated with an extended multiangle dynamic light scattering (DLS) setup. The DLS setup was equipped with a conventional laser (λ = 633 nm) to determine the microgel particle size. Additionally, a laser (λ = 532 nm) is installed to study the photoresponsive behavior of the AuNP-microgel hybrids. The wavelength of 532 nm is close to the absorption maximum of the plasmon resonance of the AuNPs used in the present study (i.e. spherical AuNPs with a diameter of 14 nm). The extended DLS setup enables us to follow in situ the change in microgel size during irradiation. The light stimulus is directly correlated with the size changes of the hybrid particles and the photothermal effect depends on the intensity of the excitation laser. The increase in excitation laser intensity results in a size reduction of hybrid particles because of the ability of AuNPs to partially transform the absorbed photon energy into heat which is emitted into the surrounding microgel network.

Multi-channel in situ dynamic light scattering instrumentation enhancing biological small-angle X-ray scattering experiments at the PETRA III beamline P12.

Small-angle X-ray scattering (SAXS) analysis of biomolecules is increasingly common with a constantly high demand for comprehensive and efficient sample quality control prior to SAXS experiments. As monodisperse sample suspensions are desirable for SAXS experiments, latest dynamic light scattering (DLS) techniques are most suited to obtain non-invasive and rapid information about the particle size distribution of molecules in solution. A multi-receiver four-channel DLS system was designed and adapted at the BioSAXS endstation of the EMBL beamline P12 at PETRA III (DESY, Hamburg, Germany). The system allows the collection of DLS data within round-shaped sample capillaries used at beamline P12. Data obtained provide information about the hydrodynamic radius of biological particles in solution and dispersity of the solution. DLS data can be collected directly prior to and during an X-ray exposure. To match the short X-ray exposure times of around 1 s for 20 exposures at P12, the DLS data collection periods that have been used up to now of 20 s or commonly more were substantially reduced, using a novel multi-channel approach collecting DLS data sets in the SAXS sample capillary at four different neighbouring sample volume positions in parallel. The setup allows online scoring of sample solutions applied for SAXS experiments, supports SAXS data evaluation and for example indicates local inhomogeneities in a sample solution in a time-efficient manner. Biological macromolecules with different molecular weights were applied to test the system and obtain information about the performance. All measured hydrodynamic radii are in good agreement with DLS results obtained by employing a standard cuvette instrument. Moreover, applying the new multi-channel DLS setup, a reliable radius determination of sample solutions in flow, at flow rates normally used for size-exclusion chromatography-SAXS experiments, and at higher flow rates, was verified as well. This study also shows and confirms that the newly designed sample compartment with attached DLS instrumentation does not disturb SAXS measurements.

Resolving power of dynamic light scattering for protein and polystyrene nanoparticles

Dynamic light scattering (DLS) is a non-invasive, label-free technique for the characterization of particles ranging from nanometer to micrometer size. It is widely used for the analysis of proteins to assess association states and the nature of protein aggregates. Despite its frequent use, little quantitative information on its size resolution capabilities, in particular for protein material, is available. This study explores the resolving power of a standard DLS setup for binary mixtures of latex standard particles and mixtures of protein monomer and protein particles made from cross-linked protein material. At constant instrument settings, the resolving power depends on the size ratio and the mass ratio of the species in a mixture as well as on the total concentration and the scattering characteristics of the material. In this study, we provide a summary at which parameter combinations resolution of two species with varying size is possible. These data guide the quantitative evaluation of DLS results for mixtures. We found that a mixture of an antibody monomer and protein particles of an average hydrodynamic diameter of 50 nm can be resolved at a 1–20-fold excess of monomer (by mass). A mixture of monomer and 70 nm particles can be resolved at a 2–30-fold excess, a mixture of monomer and 190 nm particles at a 200–1700-fold excess of monomer. The findings allow to better judge DLS results for protein samples of unknown composition.

Ultralow-angle dynamic light scattering with a charge coupled device camera based multispeckle, multitau correlator

We use a charge coupled device (CCD) camera and a multi-tau software correlator to measure dynamic light scattering (DLS) at many angles simultaneously, from 0.07° to 5.1°. Real-time autocorrelation functions are calculated by averaging both over time and over CCD pixels, each corresponding to a different coherence area. In order to cover the wide spectrum of decay times associated with the large range of accessible angles, we adopt the multitau scheme, where the correlator channel spacing is quasilogarithmic rather than linear. A detailed analysis is presented of the effects of dark noise, stray light, and finite pixel area, and methods to correct the data for these effects are developed, making a CCD camera a viable alternative for a DLS detector. We test the apparatus on a dilute suspension of colloidal particles. Very good agreement is found between the particle radius derived from the CCD data, and that obtained with a conventional DLS setup.

Collective membrane motions of high and low amplitude, studied by dynamic light scattering and micro-interferometry.

Undulations of lipid bilayers were experimentally studied for the two limiting cases of high and weak lateral tension using two well established model systems: freely suspended planar lipid bilayers, so-called black lipid membranes (BLM) for high-tension studies and large unilamellar vesicles (LUV) for measurements at weak tension. This variation in tension results in changes of undulation amplitudes from several hundred nm (LUV) down to 1 nm (BLM), thus requiring different physical methods for their detection. We have employed microinterferometric techniques (RICM) for studying the regime of weak tension and dynamic light scattering (DLS) for that of high tension. The dedicated DLS set-up allowed the measurements of undulations over a wide wave vector range of 250 < q/cm-1 < 35,000 cm-1. This enabled the observation of collective membrane modes in two regimes, the oscillating one at low q and the overdamped regime at high q. The transition between both regimes at the bifurcation point is rather abrupt and depends on the lateral tension of the bilayer, as is demonstrated by comparing the dispersion curves of pure lipid and of lipid-cholestrol BLMs over the same q-range. The DLS measurements allowed a critical test of a hydrodynamic theory of the dispersion behaviour of membrane collective modes under tension. The DLS measurements are compared with RICM results of undulatory excitations of giant vesicles weakly adhering to substrates in the 10(-6)-2.5 x 10(-7) m wavelength regime and at low frequencies (0.1-25 Hz). Experimental evidence for the strong decrease in the relaxation rate by the hydrodynamic coupling of the membrane with the wall is established.

Measurement of inherent particle properties by dynamic light scattering: introducing electrorotational light scattering

Common dynamic light scattering (DLS) methods determine the size and zeta-potential of particles by analyzing the motion resulting from thermal noise or electrophoretic force. Dielectric particle spectroscopy by common microscopic electrorotation (ER) measures the frequency dependence of field-induced rotation of single particles to analyze their inherent dielectric structure. We propose a new technique, electrorotational light scattering (ERLS). It measures ER in a particle ensemble by a homodyne DLS setup. ER-induced particle rotation is extracted from the initial decorrelation of the intensity autocorrelation function (ACF) by a simple optical particle model. Human red blood cells were used as test particles, and changes of the characteristic frequency of membrane dispersion induced by the ionophore nystatin were monitored by ERLS. For untreated control cells, a rotation frequency of 2 s-1 was induced at the membrane peak frequency of 150 kHz and a field strength of 12 kV/m. This rotation led to a decorrelation of the ACF about 10 times steeper than that of the field free control. For deduction of ERLS frequency spectra, different criteria are discussed. Particle shape and additional field-induced motions like dielectrophoresis and particle-particle attraction do not significantly influence the criteria. For nystatin-treated cells, recalculation of dielectric cell properties revealed an ionophore-induced decrease in the internal conductivity. Although the absolute rotation speed and the rotation sense are not yet directly accessible, ERLS eliminates the tedious microscopic measurements. It offers computerized, statistically significant measurements of dielectric particle properties that are especially suitable for nonbiological applications, e.g., the study of colloidal particles.