Simultaneous Size and ζ-Potential Measurement
Charge example

Simultaneous size and zeta potential measurements of five different polystyrene standards. Each dot represents a single particle.

Izon’s TRPS technique enables the size and ζ-potential of individual particles to be simultaneously extracted from the resistive pulse signal they generate as they pass through a nanopore.  Collecting the information of hundreds to thousands of particles over the short analysis time (that comes with using TRPS) enables a very high resolution and accurate measurement of the overall sample distribution. 

The zeta potential of each particle can be calculated from the measured electrophoretic mobility using the Smoluchowski equation. The magnitude of the resistive pulse is independent of the respective particle zeta potential, allowing simultaneous and decoupled size and charge measurements to be carried out. This enables a truly unique approach for investigating particle properties. 

Read the white paper (click here) on TRPS measurements for more on the theory of charge measurements.

TRPS charge comparisonComparison of TRPS and PALS analyses of bimodal Zeta potential samples

Comparison with other Methods

Other measurement methods commonly used for zeta potential measurements cannot resolve the charge of individual particles.  With TRPS the difference in resolution from particle by particle charge is obvious. In the below example, analysis of the two samples of near neutral polystyrene particles (CPN400) and negatively charged carboxylated (CPC400) particles (traces as labelled for PALS data; blue and green data points for TRPS data respectively) show good agreement between the two techniques. However, when the two populations were mixed to give a bimodal sample, PALS was unable to resolve the two populations, due to it being an averaging technique (bottom trace). In contrast, TRPS shows two distinct populations (red data points), which agree well with the zeta potential values of unmixed samples.