One of the most significant applications for Malvern
Instruments’
new Zetasizer Nano ZSP dynamic light scattering system is the highly
sensitive measurement of the zeta potential, or electrophoretic
mobility, of proteins. The instrument delivers unique performance
specifications for both size and zeta potential measurement, employing
an approach to zeta potential measurement that accords with the latest
industry guidance.
Published during 2012, standard guide ASTM E2865 deals with the
measurement of mobility and zeta potential in systems containing
biological material such as proteins, DNA, liposomes and other similar
organic materials that possess particle sizes in the nanometer scale,
below 100 nm. These materials are often labile, especially when
subjected to an electric field, and standard electrophoretic techniques
can lead to measurement of the resulting aggregates rather than the
native material.
It has been shown that much of the aggregation takes place at the
electrodes. In the Zetasizer Nano ZSP, use of Malvern’s patented
Diffusion Barrier Technique protects the sample by isolating it from
the electrode, as recommended in the ASTM standard. Consequently the
applied voltage can be switched on for longer periods to generate more
reliable measurement data. The method involves the use of a unique,
disposable folded capillary cell which allows measurements to be
conducted on samples as small as 20 microliters.
The measurement process is simplified by the inclusion of a protein
mobility measurement type in the instrument software that controls data
acquisition, guides the user through the measurement and assesses and
reports on data quality. Additional tools in the software also allow
calculation of protein charge, as illustrated here:
Further details of the benefits of the Diffusion Barrier Technique
for protein mobility measurements can be found on the Malvern
website.
Full details of ASTM E2865 are
available here.