Dynamic light scattering (DLS) measures time-dependent fluctuations in the scattering intensity arising from particles undergoing random Brownian motion. Diffusion coefficient and particle size information can be obtained from the analysis of these fluctuations. This paper discusses the factors which will influence the lower size limit of DLS and reports the use of sucrose as a test sample to probe this lower limit of the technique. Hydrodynamic diameter values of less than 1 nm are obtained by the use of 173°backscatter detection that is applied to increase the sensitivity of DLS. The peak means (with standard deviations) obtained for the intensity and volume data from a series of sucrose concentrations, ranging from 5 to 35% w/v, were measured as D I,Mean = 0.82 nm (0.11 nm) and D V,Mean = 0.62 nm (0.05 nm), respectively. These sucrose results suggest that sub nanometer measurements are achievable with a precision of 0.1 nm. Evidence to support these size results for sucrose is discussed.

Harding (2007) Dynamic light scattering as a relative tool for assessing the molecular integrity and stability of monoclonal antibodies, Biotechnology and Genetic Engineering Reviews, 24:1, 117-128,

Dynamic light scattering (DLS) is a technique used for measuring the size of molecules and particles undergoing Brownian motion by observing time‐dependent fluctuations in the intensity of scattered light. The measurement of samples using conventional DLS instrumentation is limited to low concentrations due to the onset of a phenomenon called multiple scattering. The problems of multiple scattering have been addressed in a light scattering instrument incorporating non‐ invasive backscatter optics (NIBS). This novel optic arrangement maximizes the detection of scattered light while maintaining signal quality and allows for measurements of turbid samples. This paper discusses the ability of backscatter detection to accurately determine particle sizes at 1 %w/v sample concentrations and demonstrates the correct resolution of different size populations using a series of latex standard mixtures with known volume ratios. The concentration of 1 %w/v is much higher than can be measured on conventional dynamic light scattering instruments.

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The technique of dynamic light scattering is well suited to the measurement of the size of colloidal dispersions. Traditionally, measurements of large particle sizes or particles that are highly scattering would require high dilution of the sample in order to avoid multiple scattering effects. Conversely, measurement of very small and/or poorly scattering particles or samples that are very dilute are difficult unless high‐powered lasers are used. These problems have been addressed in a light scattering instrument incorporating novel non‐invasive backscatter optics (NIBS). This novel optic arrangement maximises the detection of scattered light while maintaining signal quality. In addition to the increased size and concentration range for DLS applications, the increased sensitivity obtained from this optical arrangement also allows for the determination of absolute molecular weight using static light scattering measurements. Accurate molecular weight measurements can be achieved at a single scattering angle for molecules that do not show any angular dependence in their scattering intensity. This paper describes the advantages of using backscatter optics and illustrates the capabilities of the technology by reporting results of measurements from various applications.

A new technique for the measurement of protein mobility using laser Doppler electrophoresis (LDE) is introduced and characterised. The diffusion barrier approach loads a tiny protein sample volume into a much larger volume of dispersant, which contains the electrodes; the LDE measurement is then recorded before the sample can diffuse to the electrodes. We demonstrate that sample volumes are reduced by up to two orders of magnitude to volumes typically associated with separation techniques (∼50 μL), no reduction in measurement sensitivity occurs, samples can be retrieved usefully intact, post-measurement and typical measurement times are of the order of minutes. Measurements of BSA mobility up to 75°C and 1 M buffer concentration and lysozyme at a concentration as low as 0.5 mg/mL are demonstrated using the technique with good agreement with literature values.

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The validity of a simple chronoamperometric technique for measuring the electrophoretic mobilities of colloid particles has been established by comparison of the results with those obtained from photon correlation spectroscopy, a well established method. Resolution of several flaws in the theory underlying chronoamperometric electrophoresis has led to a rationale of electrophoretic deposition based on turbulent liquid flow. The new theory also accounts for observations regarding the charge-transfer processes necessarily accompanying particle deposition.