DLS is a powerful and versatile tool for characterizing particles and macromolecules in dispersion, and this is aided by the range of accessories available for sample presentation, including multiple options for cuvettes. The use of cuvettes means that presentation of the sample to the DLS instrument is simple and contamination free, however in some applications, disposable cuvettes may be preferred to avoid the need for cleaning.
Whilst disposable plastic cuvettes are convenient, they offer lower optical quality which may impact on data quality, particularly for low scattering samples, and may not be compatible will all dispersants of interest.
The new Low Volume Disposable Sizing Cell (LVDSC) addresses this compromise by allowing high quality measurements to be made using a disposable glass capillary, which allows measurements with sample volumes as small as 3 µl.
The LVDSC comprises a metal body holder and a glass capillary with a 1mm bore which is square in cross section. The specially designed holder ensures reliable and repeatable positioning of the capillary within the Zetasizer Ultra, without the need for modification to the cell area, as well as facilitating thermal contact. The capillary is most easily loaded by dipping to tip of the capillary into the sample, which is then drawn up by capillary action. Typically, between 10 and 30 µl of sample will be drawn into the capillary.
To measure a 3 µl aliquot, the sample should be loaded using a pipette fitted with a gel tip, which can be placed inside the end of the capillary.
With the small size of the capillary, and significant reduction in cost when compared with conventional glass or quartz cuvettes, we may anticipate some degradation in data quality. This may potentially be of detriment when measuring low scattering samples such as low concentration proteins.
Results for repeat measurements of a 1 mg/ml dispersion of Hen’s egg lysozyme, dispersed in pH 4.0 Acetate buffer, measured in both a 10mm quartz cuvette and the low volume disposable sizing cell, show comparison between the measurements performed in each cell show very good agreement and no sign of difference in data quality, despite the 300-fold difference in sample volume.
The low volume disposable sizing cell may be easily loaded with up to 30 µl of sample by capillary action, however sample volumes as low as 3 µl can be achieved by loading the sample using a pipette directly into the capillary. Such measurements show uncompromised data quality, with measurements of low scattering, fragile samples being consistent with those performed on much larger volumes in conventional high-quality cuvettes.
The ability to measure such low volumes in a disposable manner is expected to be particularly useful in bio-pharm applications, where the total available volume of samples to be analyzed may be small, and cross contamination is a concern.
