Need help figuring this equation

[aruwin]

Hi.
I am doing some experiment on finding the electrical characteristics (surface conductance specifically) of a particle which is then attached to different amount of DNAs. The whole aim of this experiment is actually to analyse the sensitivity of this new found method of detecting DNA, but I don't think I need to explain it in detail for this particular problem.
Now, this zeta potential is crucial because it's needed to calculate the crossover frequency of the DNA-attached particles. Crossover frequency is the frequency at which dielectrophoresis force is 0 (neither positive nor negative).
After measuring the zeta potential of the particles, it was found that the zeta potential didn't show a significant change despite changing the ratio of particle to DNA. The crossover frequency however, did show a change corresponding to the different ratios of particle to DNA. Why is this so? And that's what I need to figure out. I am not so good at math so I am helping someone could solve this question, please. I guess the answer could be found by analysing this equation.

The equation is attached.

 

[jvicens]

Hello,

Thank you for sharing your experiment with us. It sounds like you are working on a very interesting project. I would be happy to offer some insights on why the zeta potential did not show a significant change, but the crossover frequency did.

Firstly, let's briefly discuss what zeta potential and crossover frequency are. Zeta potential is a measure of the electrical charge present on the surface of a particle, while crossover frequency is the frequency at which the dielectrophoresis force on a particle is zero. Dielectrophoresis is the movement of a particle in an electric field due to its polarizability.

Now, let's take a look at the attached equation. This equation relates the zeta potential to the crossover frequency and other factors such as the particle size and the permittivity of the medium. As you can see, the zeta potential is directly proportional to the crossover frequency. This means that as the crossover frequency increases, so does the zeta potential. However, the equation also includes the particle size and the permittivity of the medium, which can affect the zeta potential and crossover frequency independently.

In your experiment, you changed the ratio of particle to DNA, but it is possible that the particle size remained constant. This could explain why the zeta potential did not show a significant change, as it is influenced by both the ratio of particle to DNA and the particle size. However, the crossover frequency did show a change, indicating that the dielectrophoresis force was affected by the changing ratio of particle to DNA. This could be due to changes in the permittivity of the medium caused by the attachment of DNA molecules to the particle.

In conclusion, the reason for the difference in the results for zeta potential and crossover frequency could be due to the fact that they are influenced by different factors, such as particle size and permittivity of the medium. I would recommend further investigating these factors and their effects on zeta potential and crossover frequency in your experiment.

I hope this helps and good luck with your research!