Dear All
I prepare pDNA-poly l lysine (PLL) nanoparticels in nuclesse free water and measure their zetapotential in the same media without dilution. The PLL comes as hydrobromide salt ( so -ve Br in the solution). The results gives me around +ve 25 mV. Is it safe to say that without having NaCl in the solution the results are ok? Due to having lots of -ve Br in the solution which will bind to the pDNA-PLL nanoparticles and give this result. By the way these nanoparticles are expected to be positively charged.
I want to check that my results are valid and whether it is possible for the Br ions to bind to these nanoparticles.
I can not add NaCl because it will affect pDNA-PLL nanoparticle formation.
Appreciate your input.
https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/zeta-potential
May above link to be helpful in the understanding of zeta potential
Excess of Br- are trouble! Check the reactivity scale at molar ratio for your preparation. Also, in an aliquot, confirm the presence of Br- ions and/or try neutralizing (based on calculated stoichiometry, at least empirical) the reaction/preparation media 's part. Adding of NaCl in aqueous environment with Br- ions around is not of much help! The check will provide the real potential value, and if you are expecting +ve, it may significantly change!
Riaz A. Khan thanks for your reply. I forgot to mention I have excess of +vely charged PLL as well (there is 12 PLL and 12 Br for every 1 -ve charge of DNA, only 1 PLL binds to DNA and the rest 12/11 Br/PLL is left in solution). I was only concerned because the recomendation is to measure in 1-10mM NaCl.
Aveen Jalal Without quoting pH, the zeta potential results have little significance.
Aveen Jalal You state 'By the way these nanoparticles are expected to be positively charged'. The zeta potential is measured at the slipping plane (not the surface of the particle) so a positively charged particle will have a cloud of strongly attached negative ions that will move/diffuse with it. Understand possible reactions between Cl- and Br- with your electrodes - which are made of what?
Alan F Rawle What I mean is the zeta potential is expected to be +ve
I use the folded capillary cells and zetasizer NanoZs. I am assuming that there is another layer (Diffuse layer) of moslty opposit charge to Cl- and Br- ( Stern layer) that will draw the particles (with layers) to the -ve electrode
If I understand your question correctly, you are concerned about the quality of your measurement data. Aside from making repeated measurements, please take a look at https://www.materials-talks.com/blog/2015/09/24/zeta-deviation-larger-than-the-mean-how-can-that-be/ and https://www.materials-talks.com/blog/2017/09/05/what-is-the-zeta-deviation/ which also contains a link to the zeta quality report. The scattering signal from ions will be so much smaller than the scattering signal from the nanoparticles. You should - provided there is nothing else wrong with your experiment - detect mostly the scattering from the nanoparticles, and their zeta potential.
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