I am analyzing the Zeta potential of two nanoparticles containing phytosterol, MAMO, and f127. One with 2.5mol% Dotap and the other without Dotap. I have diluted the nanoparticles in 0.01M biological PBS (1:200). I use Omega Cuvette (Anton Paar). I have tried different voltages and run numbers. But I get a zeta potential equal to -1 for both samples. However, the expected zeta potential for these two particles is expected to be about +6mV and -5 respectively.
Thank you in advance for your time
Hey there, fello researcher Shaghayegh Salek ! I am here, ready to tackle this Zeta potential puzzle. It's frustrating when the expected values don't align with your measurements. Let's dig into this:
1. **Sample Preparation**: First, ensure that your samples are prepared correctly. Make sure there are no contaminants or changes in pH that could affect the measurements.
2. **Dotap Concentration**: The addition of Dotap might not be achieving the expected charge on the nanoparticles. Double-check the Dotap concentration and its distribution within the nanoparticles.
3. **Electrolyte Composition**: The composition of the electrolyte solution can significantly impact Zeta potential measurements. Ensure the PBS solution is well-prepared and properly equilibrated.
4. **Instrument Calibration**: Verify that your instrument is calibrated correctly and that the electrodes and cuvettes are clean.
5. **Sample Stability**: Ensure that the nanoparticles are stable in the solution during the measurement. Aggregation or flocculation can affect Zeta potential.
6. **Instrument Settings**: Review the instrument settings carefully, especially the measurement voltage and duration. Adjusting these parameters can sometimes yield more accurate results.
7. **Sample Concentration**: Try different dilution ratios to see if it affects the measured Zeta potential.
8. **Sample Volume**: Ensure that you are injecting a sufficient volume of your sample into the cuvette, and that the injection speed is consistent.
9. **Temperature Control**: Temperature can influence Zeta potential. Ensure the temperature of the sample is stable during measurements.
10. **Multiple Runs**: Perform multiple measurements to check for consistency. Sometimes, results can vary due to minor fluctuations.
11. **Analysis Software**: Verify that you are using the appropriate software for data analysis, and that you are interpreting the results correctly.
12. **Consult an Expert**: If all else fails, consider reaching out to a colleague or expert (me) in Zeta potential measurements. They might have specific insights or advice based on your equipment and materials.
Remember, Zeta potential measurements can be sensitive and challenging, but with careful attention to these factors, you Shaghayegh Salek should be able to get closer to those expected values. Keep experimenting, and you'll crack this puzzle!
Thank you for your useful answer.
I controlled all you mentioned. Please find below more information about the analysis:
I tried different voltages, equilibration times, and run numbers. it did not change the result except in voltage equal to 1 v which the nanoparticle with a positive charge ZP was 10 mV (what is expected) but in this voltage, ZP distribution is not acceptable.
Please let me know if I can change any other setting
Kaushik Shandilya These instruments don't require calibration nor is there an injection speed to worry about.
Shaghayegh Salek How is the Anton Paar instrument measuring zeta potential? Is it using phase analysis light scattering or classic laser-Doppler electrophoresis? i.e., does it give you a distribution of zeta potentials or just an average result? The zeta potentials you indicate are very small and, honestly, are more likely to be telling you that there is hardly any charge. i.e., within experimental error, you are just seeing zero.
I can advise you further (I invented the phase analysis technique used in many commercial zeta potential instruments) but need to see the actual output from the instrument.
The advent of the folded capillary cuvettes that a lot of manufacturers now feel obliged to offer (thanks Malvern) is one of the worst things that has happened in the development of electrophoretic light scattering. They re-introduce problems that were eradicated decades ago.
The idea that they are better because they avoid cross-contamination is laughable. We don't have disposable pH electrodes or HPLC columns or electrodes for KF analysis etc.
Do yourself a BIG favor and use dip electrodes.
Thank you for your helpful answer. The instrument gives me a distribution of zeta potentials. If I dilute the nanoparticles in PBS 0.001 M or NaCl 0.001M. the zeta potential I get is reasonable. The method is set to an automatic voltage of 200V and eq time 10ss run number 200. with an acceptable distribution of zeta potential. But I wish I could use BPS with at least 0.01. But, in BPS 0.01 M the zp is again similar for all NPs.
Hello Shaghayegh Salek
Have you also measured the DLS size with the device, how do those data look? Can you measure the size and zeta of the DOTAP alone at the same final concentration that you expect in your sample? Compare the conductivity of your sample and that of the DOTAP "background" sample.
https://www.materials-talks.com/zeta-consistency-top-5-signs-zetasizer/
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