I have prepared a few formulations of drug loaded polymer particles by varying the amount of crosslinker. It was observed that the size of the nanoparticles decreased initially with the increase in the amount of crosslinker to a certain extent but the size increased with further increase in the amount of crosslinker. Moreover, some of these formulations seemed unstable having negative zeta potential value around 2 mV.
Hello Bably Khatun ,
zeta potential is a measure of the effective charge of particles in solution. Zeta potential and size are not directly related. However, if the formulation is primarily stable due to electrostatic repulsion of particles then there can be some correlation between zeta and size. In such cases, a stronger zeta (absolute value) can correspond with a "smaller" particle size. And a weaker zeta (near zero) may correspond with a "larger" particle size. In other words, a zeta potential of 2mV may lead to aggregation, and thus an overall larger size as measured by DLS. You may find this post on zeta of interest: https://www.materials-talks.com/blog/2017/09/05/what-is-the-zeta-deviation/
An additional effect when formulating may be the influence of overall conductivity, see https://www.materials-talks.com/blog/2018/03/06/zeta-potential-in-salt-solution-or-any-other-ions/
There is also an application note on a titration of BSA versus pH which illustrates experimentally how size and zeta may vary, on the Malvern Panalytical site https://www.malvernpanalytical.com/en/learn/knowledge-center/application-notes/AN101104AutomatedProteinCharacterization.html
Bably Khatun
I suggest reading the article we recently published: Zeta Potential and Colloidal Stability Predictions for Inorganic Nanoparticle Dispersions: Effects of Experimental Conditions and Electrokinetic Models on the Interpretation of Results. doi.org/10.1021/acs.langmuir.1c02056.
In summary, for most systems, the determination of the zeta potential strongly depends on the particle size (mainly for nanoparticles). Most of the zeta potential values reported in the literature use the Helmholtz-Smoluchowski model to calculate the zeta potential. This approximation assumes that the particle is large enough to overlook the particle curvature effect during the calculation. However, this assumption is not valid for nanoparticles. In addition, particle size can contribute to other phenomena that develop during a zeta potential measurement, such as relaxation effects, electrical double layer polarization, and surface conduction. Therefore, neglecting the particle size effect and its associated effects can lead to zeta potential values that are grossly wrong.
To exemplify this difference, a model that considers the effect of particle size and its associated effects in calculating the zeta potential will provide a zeta potential value that can be two times greater than the value provided by the Helmholtz-Smoluchowski model, which does not consider the effect of particle size.
Sincerely,
Daniel José Pochapski
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