Dynamic Light Scattering Instrument Research Articles

Techniques for Accurate Sizing of Gold Nanoparticles Using Dynamic Light Scattering with Particular Application to Chemical and Biological Sensing Based on Aggregate Formation.

Gold nanoparticles (AuNPs) have found broad applications in chemical and biological sensing, catalysis, biomolecular imaging, in vitro diagnostics, cancer therapy, and many other areas. Dynamic light scattering (DLS) is an analytical tool used routinely for nanoparticle size measurement and analysis. Due to its relatively low cost and ease of operation in comparison to other more sophisticated techniques, DLS is the primary choice of instrumentation for analyzing the size and size distribution of nanoparticle suspensions. However, many DLS users are unfamiliar with the principles behind the DLS measurement and are unware of some of the intrinsic limitations as well as the unique capabilities of this technique. The lack of sufficient understanding of DLS often leads to inappropriate experimental design and misinterpretation of the data. In this study, we performed DLS analyses on a series of citrate-stabilized AuNPs with diameters ranging from 10 to 100 nm. Our study shows that the measured hydrodynamic diameters of the AuNPs can vary significantly with concentration and incident laser power. The scattered light intensity of the AuNPs has a nearly sixth order power law increase with diameter, and the enormous scattered light intensity of AuNPs with diameters around or exceeding 80 nm causes a substantial multiple scattering effect in conventional DLS instruments. The effect leads to significant errors in the reported average hydrodynamic diameter of the AuNPs when the measurements are analyzed in the conventional way, without accounting for the multiple scattering. We present here some useful methods to obtain the accurate hydrodynamic size of the AuNPs using DLS. We also demonstrate and explain an extremely powerful aspect of DLS-its exceptional sensitivity in detecting gold nanoparticle aggregate formation, and the use of this unique capability for chemical and biological sensing applications.

Dynamics of liquid-crystalline emulsion droplets arrested in hydrogels: Addressing the multiple scattering problem in turbid systems

Abstract Performing dynamic light scattering (DLS) measurements on turbid samples is still a great challenge. A standard DLS instrument will provide reliable measurements as long as the sample is transparent and ergodic. Measurements on highly concentrated systems, on the other hand, such as glasses or gels, show partially frozen dynamics or incomplete relaxation processes. Such systems are called nonergodic. Nonergodic systems commonly appear in various practical applications and are therefore of great scientific as well as industrial interest. Many of these systems show high turbidity caused by the multiple scattering. The contribution of multiple scattering accompanied by low light transmission often leads to false DLS results for such systems, since standard DLS theory is only valid for single-scattered light. We describe here a DLS instrument that has been modified to address this problem. We use a charge-coupled device (CCD) camera as a multispeckle detector, and combine single-mode fiber optics with a photomultiplier to determine both ensemble and time-averaged autocorrelation functions. The instrument features a thin, flat sample cell with a translation stage. We show some DLS results for a series of turbid colloidal suspensions, where the lipid droplets are entrapped in polymeric hydrogels of different polymer concentrations. We focus on the transition from ergodicity to nonergodicity using ensemble-averaged DLS-intensity autocorrelation functions.

Dynamic light-scattering measurement comparability of nanomaterial suspensions

Increased use of nanomaterials in everyday products leads to their environmental release and therefore, the information need on their fate and behaviour. Nanomaterials have to be suspended with high repeatability and comparability for studies on environmental effects. They also have to be well characterised with a focus on the state of agglomeration and particle size distribution. Dynamic light-scattering (DLS) is a common technique used for these measurements. If suspensions are prepared in different laboratories, then concern has risen about the comparability of the measured results, especially when different DLS instruments are used. Therefore, for quality assurance, a round-robin test was conducted to assess the comparability of different DLS instruments and a dispersion protocol in ten independent laboratories. Polystyrene and TiO2 were chosen as test (nano)materials. For the comparability of the DLS instruments, the average sizes of the PSL and a stabilised TiO2 suspension were measured. The measured average hydrodynamic diameter shows an overall good inter-laboratory comparability. For the PSL suspension, an average hydrodynamic diameter of 201 ± 13 nm and for the TiO2 suspension an average diameter of 224 ± 24 nm were detected. For the TiO2 suspension that was prepared at each laboratory following an established suspension preparation protocol, an average hydrodynamic diameter of 211 ± 11 nm was detected. The measured average particle size (mode) increased up to 284 nm with a high standard deviation of 119 nm if the preparation protocol could not established and different procedures or different equipment were employed. This study shows that no significant differences between the employed DLS instrument types were determined. It was also shown that comparable measurements and suspension preparation could be achieved if well-defined suspension preparation protocols and comparable equipment can be used.

Measuring the lateral size of liquid-exfoliated nanosheets with dynamic light scattering

We have developed an in situ method to estimate the lateral size of exfoliated nanosheets dispersed in a liquid. Using standard liquid exfoliation and size-selection techniques, we prepared a range of dispersions of graphene, MoS2 and WS2 nanosheets with different mean lateral sizes. The mean nanosheet length was measured using transmission electron microscopy (TEM) to vary from ∼40 nm to ∼1 μm. These dispersions were characterized using a standard dynamic light scattering (DLS) instrument. We found a well-defined correlation between the peak of the particle size distribution as outputted by the DLS instrument and the nanosheet length as measured by TEM. This correlation is consistent with the DLS instrument outputting the radius of a sphere with volume equal to the mean nanosheet volume. This correlation allows the mean nanosheet length to be extracted from DLS data.

Specific Soluble Oligomers of Amyloid-β Peptide Undergo Replication and Form Non-fibrillar Aggregates in Interfacial Environments

Aggregates of amyloid-β (Aβ) peptides have been implicated in the etiology of Alzheimer disease. Among the different forms of Aβ aggregates, low molecular weight species ranging between ~2- and 50-mers, also called "soluble oligomers," have emerged as the species responsible for early synaptic dysfunction and neuronal loss. Emerging evidence suggests that the neurotoxic oligomers need not be formed along the obligatory nucleation-dependant fibril formation pathway. In our earlier work, we reported the isolation of one such "off-pathway" 12-18-mer species of Aβ42 generated from fatty acids called large fatty acid-derived oligomers (LFAOs) (Kumar, A., Bullard, R. L., Patel, P., Paslay, L. C., Singh, D., Bienkiewicz, E. A., Morgan, S. E., and Rangachari, V. (2011) PLoS One 6, e18759). Here, we report the physiochemical aspects of LFAO-monomer interactions as well as LFAO-LFAO associations in the presence of interfaces. We discovered that LFAOs are a replicating strain of oligomers that recruit Aβ42 monomers and quantitatively convert them into LFAO assemblies at the expense of fibrils, a mechanism similar to prion propagation. We also found that in the presence of hexane-buffer or chloroform-buffer interfaces LFAOs are able to associate with themselves to form larger but non-fibrillar aggregates. These results further support the hypothesis that low molecular weight oligomers can be generated via non-fibril formation pathways. Furthermore, the unique replicating property of off-pathway oligomers may hold profound significance for Alzheimer disease pathology.

Supercritical Antisolvent-based Technology for Preparation of Vitamin D 3 Proliposome and Its Characteristics

Vitamin D 3 (VD 3) proliposomes (VDP), consisted of hydrogenated phosphatidycholine (HPC) and VD 3, were prepared using supercritical anti-solvent technology (SAS). The effects of operation conditions (temperature, pressure and components) on the VD 3 loading in VDP were studied. At the optimum conditions of pressure of 8.0 MPa, temperature of 45°C, and the mass ratio of 15.0% between VD 3 and HPC, the VD 3 loading reached 12.89%. VD 3 liposomes (VDL) were obtained by hydrating VDP and the entrapment efficiency of VD 3 in VDL reached 98.5%. The morphology and structure of VDP and VDL were characterized by SEM (scanning electron microscope), TEM (transmission electron microscope) and XRD (X-ray diffractometer). The structure of VD 3 nanoparticles in HPC matrix was formed. The size of VDL with an average diameter of about 1μm was determined by dynamic light scattering instrument (DLS). The results indicated that VDP can be made by SAS and VDL with high entrapment efficiency can be formed easily via the hydration of VDP.

Systematic study of bimodal suspensions of latex nanoparticles using dynamic light scattering

Determining the size of nanoparticles accurately, quickly and easily is becoming more and more important as the use of such particles increases. One of the common techniques for measuring the size of particles in suspension is dynamic light scattering (DLS). In principle, DLS is able to estimate the hydrodynamic particle diameter and its intensity-weighted distribution. However, the measured correlation function or power spectrum must be inverted to obtain this size distribution. The inversion is an ill-posed mathematical problem, and only under certain assumptions can the distribution be determined reliably. Suspensions containing bimodal (or multi-modal) particle size distributions are particularly challenging. This study reports on DLS measurements on a range of bimodal distributions of latex spheres with varying ratios of particle sizes. To determine the efficacy of different inversion techniques, the data has been analyzed both with the algorithms implemented in the DLS instrument’s proprietary analysis software and with other inversion routines based on simple analytical models of the particle size distribution. In addition, the results of the DLS analysis have been compared to scanning and transmission electron microscopy (SEM and TEM) measurements.

Reliable size determination of nanoparticles using dynamic light scattering method for in vitro toxicology assessment

Dynamic light scattering (DLS) is widely used for the evaluation of the particle size in the toxicity assessment of nanoparticles. However, the many types of DLS instruments and analytical procedures sometimes give different apparent sizes of particles and make it complicated to understand the size dependence on particles for the toxicity assay. In this study, we established an evaluation method of secondary nanoparticle sizes using a DLS analysis. First, we established a practical method for determining size with an appropriate evaluation of uncertainties. This proposed method could be a universal protocol for toxicity assessment that would allow researchers to achieve some degree of concordance on the size of nanoparticles for an assessment. Second, we investigated the processes associated with particles in suspension by examining the changes in the size and the light scattering intensity of secondary nanoparticles during an in vitro toxicity assessment, since the transport mode of particles to cells is significant in understanding in vitro nano-toxicity. In this study, these two points were investigated on TiO 2 nanoparticles suspension as an example. The secondary particles of TiO 2 with a light scattering intensity-averaged diameter ( d l ) of 150–250 nm were characterized with appropriate uncertainties. The sizes were found to be comparable with values determined using other analytical procedures and other instruments. It is suggested that d l could be an effective size parameter for toxicity assessments. Furthermore, TiO 2 secondary nanoparticle suspensions are well dispersed with slow gravity settling, no agglomeration, with the diffusion process as the primary transport mode of particles to cells.

A versatile, low-cost approach to dynamic light scattering

We describe a method for constructing a fiber-optic-based dynamic light scattering (DLS) instrument from commonly available components, without a need for custom-made parts. Details are provided that allow for academic researchers from diverse backgrounds to build this DLS instrument with minimal effort and at a low cost. This approach, while providing good sensitivity and high accuracy (e.g., measuring the size of latex standards to within 1% relative standard deviation), possesses several advantages not found, in their entirety, in existing DLS instrumentation. It was observed that, even though an arbitrary scattering angle could be selected, aligning this instrument to obtain optimal detection efficiency can be completed in as little as a few minutes. Also, complications associated with light refraction at the sample cell interface are avoided. Small volumes (<10 µL) can be measured, for example, by hanging a solution droplet from the fiber optic probe tips. In addition, use of fiber optic probes allows the beam path length to be as short as 1.6 mm while measuring at 90°, which reduces the likelihood of multiple scattering. With minimal customization, compact submersible probes and a portable battery-operated DLS instrument were made as examples of potential implementation. Finally, this approach is versatile, and can be incorporated into a wide variety of reactors, for in situ characterization, and other instrumentation for hybrid measurements. This type of in situ measurement was conducted after mounting the DLS probes inside a standard three-neck flask. This allowed for direct monitoring of the growth of silica nanoparticles prepared via Stöber synthesis.

Crystal Structure of the Heme-IsdC Complex, the Central Conduit of the Isd Iron/Heme Uptake System in Staphylococcus aureus

Pathogens such as Staphylococcus aureus require iron to survive and have evolved specialized proteins to steal heme from their host. IsdC is the central conduit of the Isd (iron-regulated surface determinant) multicomponent heme uptake machinery; staphylococcal cell-surface proteins such as IsdA, IsdB, and IsdH are thought to funnel their molecular cargo to IsdC, which then mediates the transfer of the iron-containing nutrient to the membrane translocation system IsdDEF. The structure of the heme-IsdC complex reveals a novel heme site within an immunoglobulin-like domain and sheds light on its binding mechanism. The folding topology is reminiscent of the architecture of cytochrome f, cellobiose dehydrogenase, and ethylbenzene dehydrogenase; in these three proteins, the heme is bound in an equivalent position, but interestingly, IsdC features a distinct binding pocket with the ligand located next to the hydrophobic core of the beta-sandwich. The iron is coordinated with a tyrosine surrounded by several non-polar side chains that cluster into a tightly packed proximal side. On the other hand, the distal side is relatively exposed with a short helical peptide segment that acts as a lip clasping onto almost half of the porphyrin plane. This structural feature is argued to play a role in the mechanism of binding and release by switching to an open conformation and thus loosening the interactions holding the heme. The structure of the heme-IsdC complex provides a template for the understanding of other proteins, such as IsdA, IsdB, and IsdH, that contain the same heme-binding module as IsdC, known as the NEAT (near transporter) domain.