Hello friends,
I tried to measure zeta potential of bacteria in 10 mM PBS by malvern zetasizer, but during measurement both the electrodes turned black and my bacterial culture precipitated and there was no result.
Voltage applied was 40 V
I would appreciate any suggestion regarding it.
Thanks
Priyanka - That's interesting. We've done a fair amount of zeta sizing and haven't seen a similar result on the electrodes.
My first recommendation is to do the sizing in water rather than in PBS. I'm doubtful that will solve the electrode fouling, but it does simplify the measurement. The zeta sizer needs to understand your solvent in order to 'do the math' for it's estimate of zeta size. The net -3 charge on phosphate complicates the situation for several reasons, including the charge shielding model. Try washing and resuspending the organism in ddH2O and using water as the solvent in the software.
My second thought is that zeta potential in our hands has been fairly sensitive to growth phase and growth conditions. The water washing step mentioned above should be done quickly so that you don't allow the organism time to start remodeling its surface. The other experimental conditions should be as tightly controlled from a growth phase/media perspective as possible. Our best results typically had about a 15% between sample variability.
Good luck, and have fun.
If possible, try - as suggested above - reducing the conductivity as it may be a way to avoid precipitation. If not already done so, aside from reducing the applied voltage you could also consider reducing the maximum number of runs, to limit exposure to Joule heating. In case the precipitation is a result of direct contact with the electrodes, the diffusion barrier method may be worth a try as well.
http://www.materials-talks.com/blog/2015/11/24/diffusion-barrier-method-the-practical-details/
Ulf has it exactly right. To add to his answer, the reason for the degradation of the bacterial on the electrodes is that the bacteria come in contact with the electrodes in a condition of high ionic strength (PBS) and high electrical field (40 V). Change to 0.001 M NaCl to reduce the conductivity and reduce the voltage (20V?). Limit the time of the experiment. In my view, though, the diffusion barrier method would be almost certain to guarantee success - the material never comes into close proximity to the electrode. As well as Ulf's blog, this application note and webinar may be of help:
http://www.malvern.com/en/pdf/secure/AN110708NovelDiffusionBarrierTechnique.pdf
(Registration needed, I suspect)
Webinar: Protein zeta potential measurements using Malvern’s new diffusion barrier method
https://www.brainshark.com/malvern/vu?pi=698451780&b=1&tx=120486&c1=22
I know the thread is old, but anyhow:
Consider that the zeta potential of a protein is a function of pH and salt concentration a, the buffer type for example TRIS or Phosphate can also change the charge dramatically even at the same pH.
Just to ensure that noon confuses zeta with membrane potential, as the latter is a function of pumps. Also consider form the work on sample heterogeneity that bulk measurements of bacterial samples are of very limited power with regards to the sample characterisation.
This recent publication may be of interest for studying zeta potential of bacteria Article Synergistic Activity of Niclosamide in Combination With Coli...
the authors Rafael Ayerbe-Algaba et al. found a stronger negative zeta potential of two bacteria in the presence of niclosamide, indicating that the drug attaches to and alters the surface charge of the bacteria.
Shouldn't the principles be same as those of microparticles / microspheres?
M. R. Mozafari No, it’s not the same. Different principles apply with labile materials.
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