Unlike standards, many sample particles have a range of zeta potential values and Z-NTA measurements can provide high resolution particle-by particle zeta potential information. This is especially critical where small changes in the zeta potential distribution have a large effect on the behavior of a nanoparticle product, or for the detailed comparison of samples which may be close to the stability threshold.
The following represents the procedure for measuring the NTA Zeta Potential standard NTA4096, derived from Malvern Zeta Potential transfer standard (DTS1235 ZP Transfer Standard) and is applicable to all NanoSight NS500 zeta potential-enabled instruments using NTA software (version 2.3 or later). It is recommended that the zeta potential of a standard material be checked at least every month. This protocol outlines how to measure the NTA Zeta Potential standard NTA4096 to check that your instrument is performing within specification.
Figure 1a: Visual of a good image, and 1b a poor image of light scatter from particles visualized with the NanoSight instrument.
The use of Advanced Analysis settings is not required.
Select an appropriate Detect Threshold setting to process the captured videos. The setting will be correct when each white dot that should be included as a particle is highlighted with a red + (Figure 2a). If the detection threshold setting is too high, the white particle dot will not contain a red cross and is not included in the data profile (Figure2 b). If the detection threshold setting is too low, there is potential that noise will be included in the data profile which is indicated as a blue cross in the image (Figure 2c).
Figure 2: Impact of changing detection threshold setting on sample analysis with NanoSight instruments with the light scatter from each particle is seen as a white dot. Each particle should be highlighted with a red + to indicate that the particle will be in included in the data set (a). If the Detection threshold setting is too high not all particles will contain the red + (b). If the setting is too low noise may be tracked and included in the data set, indicated by blue +’s (c).
Following analysis, confirm that the electro-osmosis profile is symmetrical and parabolic. An example of this is shown in Figure 3.
Figure 3: Typical electro-osmosis profile measured on the NanoSight NS500 instrument using NTA3.0 software.
NanoSight instruments produce particle-by-particle data distributions. The modal zeta potential should have a modal zeta potential value within +/- 10% of the value supplied with the sample and coefficient of variance of under 5%. A typical data profile for NTA4096 zeta potential standards is shown in Figure 4.
Figure 4: Typical expected zeta potential distribution profile for NTA4096 measured on the NanoSight NS500 zeta instrument
All NanoSight instruments are factory set for accurate data output. Provided the instrument is used as stated in the user manuals errors in size or zeta potential data should not occur. However, excessive shock or changes in any physical condition might affect the accuracy of the instrument. If this is suspected contact the Malvern helpdesk at helpdesk@malvernpanalytical.com or for US users, support.us@malvernpanalytical.com for assistance. It will be helpful to include a data report file and associated compressed sample video.
Single particle populations, such as zeta potential standards are often only described in terms of an average or modal zeta potential value. In reality however, sample particles will always have a range of values and knowledge of the full zeta potential distribution through Z-NTA measurements can provide much more information. This is especially critical where small changes in the zeta potential distribution have a large effect on the behavior of a nanoparticle product, or for the detailed comparison of samples which may be close to the stability threshold. It is recommended that the zeta potential of a standard sample is measured by zeta-NTA on a monthly basis.
For a wide range of monodisperse and complex polydisperse sample populations, the Z-NTA particle-by-particle measurement technique provides high resolution zeta potential distributions, giving you further insight into the characteristics of your sample.
