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Handle With Care: Measuring Zeta Potential on High Conductivity Protein Samples

Proteins are most commonly resuspended in solutions that are isotonic to body fluids. However, measuring zeta potential by ELS on such high conductivity solvents can lead to excessive Joule heating, causing both sample degradation and electrode damage. Here we used the robust and reusable Univette together with the Litesizer™ 500 to measure the zeta potential of lysozyme dissolved in PBS. Thanks to the patented cmPALS technology and to the Protein Mode, a software feature that introduces short breaks in the measurement, we were able to perform highly repeatable zeta potential measurements without causing electrode damage.

Zeta potential is measured by electrophoretic light scattering (ELS), which implies the application of an electric field to the sample. A common side effect of this measurement technique is the Joule heating, where electric current passes through a conductor (in this case the sample) and produces heat. The higher the conductivity of the sample, the more heat will be generated, which can potentially lead to sample degradation and electrode damage. The problem is particularly acute for biological samples, which have the double disadvantage of requiring high conductivity solvents and being highly sensitive to heat degradation.

For such samples, it is therefore crucial that the electric current is kept as low as possible and is applied for the shortest possible time. In Anton Paar’s Litesizer™ 500, the patented cmPALS technology enables stable and sensitive zeta potential measurements at lower voltages as well as shorter measurement times, hence decreasing stress to the sensitive sample. Additionally, the user can activate a software feature termed "Protein Mode", which introduces short breaks during zeta potential measurements to allow the sample to cool down. 

The Univette, a reusable cuvette designed for zeta potential measurements in high conductivity or organic solvents, is robust enough to withstand such conditions without sustaining electrode damage. 

Here we demonstrate the combined abilities of the Litesizer™ 500 and the Univette, using Kalliope™’s Protein Mode, to measure the zeta potential of the model protein lysozyme in high conductivity solvents.

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