Zeta potential is characterization technique that can be used to determine the surface charge of nanoparticles in solutions – something that is obviously of great importance when developing new drug delivery carriers. What happens is that the surface of the charged particle attracts molecules with opposite charges and binds to them. This generates a thin liquid layer around the charged particle called the Stern Layer. When the particle diffuses in the solution, it does so surrounded by an outer layer composed of loosely associated ions. Zeta potential is the term used to refer to the electrical potential of the resultant double layer.
How is zeta potential measured?
The zeta potential of a particle is determined by measuring the velocity of the charged particles drawn toward the electrode through the sample solution when an external electric field is applied. Electrophoretic light scattering (ELS) and electroacoustic determination can also be used used for ZP analysis.
ZP magnitude (typically between +100 to -100 mV) serves as a prediction of colloidal stability. Nanoparticles with values higher than 25 mV or lower than -25 mV are generally stable. Lower values tend to lead to van der Walls force mediated aggregation, coagulation or flocculation – neither of which is good news for the nanoparticle as a drug delivery system. Positive ZP particles have a long circulating half-life, while particles with negative ZP are easily cleared out of the body by the reticuloendothelial system.
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