Zeta Potential

By

T.Dilip Kumar

Ms(Pharm.)Pharmaceutics

NIPER,Raebareli

Contents

• Introduction.

• Definitions.

• Factors affecting.

• Measurement.

• DLVO Theory.

• Importance .

• Case study.

• Conclusion.

• References.

2

Introduction

• Zeta potential is a scientific termfor electrokinetic potential incolloidal dispersions.

• It is usually denoted using theGreek letter zeta (ζ), hence ζ-potential.

• The electric potential at theboundary of the double layer isknown as the Zeta potential ofthe particles and has values thattypically range from +100 mV to-100 mV.

3

Definitions

• Nernst potential: It is the potential of the solid surface itself

owing to the presence of potential determining ions.

• Nernst potential or electrothermodynamic potential is

defined as the difference in potential between the actual

surface and the electroneutral region of the solution.

• Zeta potential: It is the potential observed at the shear

plane.4

Cont..

• Zeta potential or electrokinetic potential is defined as the

difference in the potential between shear plane and

electroneutral region of the solution.

• Zeta potential is more important than nernst potential

because the electrical double layer also moves, when the

particle is under motion.

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Factors affecting zeta potential

1. pH : In aqueous media, the pH of the sample is one of the

most important factors that affects its zeta potential.

zeta potential versus pH curve will be positive at low pH and

negative at high pH. There may be a point where the plot

passes through zero zeta potential. This point is called the

isoelectric point and is very important from a practical

consideration.

2. Thickness of double layer: The thickness of the double

layer depends upon the concentration of ions in solution and

can be calculated from the ionic strength of the medium.6

Factors affecting

The higher the ionic strength, the more compressed the

double layer becomes. The valency of the ions will also

influence double layer thickness.

3. Concentration of a formulation component: The effect

of the concentration of a formulation component on the

zeta potential can give information to assist in formulating

a product to give maximum stability.

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Zeta Potential Measurement• Zeta potential is not directly measurable, it can be calculated using

theoretical models like electrokinetic phenomena and electroacoustic

phenomena.

1. Electrokinetic :An important consequence of the existence of

electrical charges on the surface of particles is that they interact

with an applied electric field. These effects are collectively defined

as electrokinetic effects.

• Electrophoresis : Zeta potential of dispersion is measured by applying

an electric field across the dispersion. Particles within the dispersion

with a zeta potential will migrate towards the electrode of opposite

charge with a velocity proportional to the magnitude of the zeta

potential. 8

Cont..

• The velocity is dependent on the strength of electric field

or voltage gradient, the dielectric constant of the medium,

the viscosity of the medium and the zeta potential.

• The velocity of a particle in a unit electric field is

referred to as its electrophoretic mobility. Zeta potential

is related to the electrophoretic mobility by the Henry

equation

UE = 2 ε z f(κa)/3η

where UE = electrophoretic mobility, z = zeta potential,

ε =dielectricconstant, η = viscosity and f(κa) =Henry’s

function.9

Cont..

• Electrophoretic light scattering: This method is most

popularly used to determine the velocity of the particles

suspended in a fluid medium under an applied electric field.

• The particles are irradiated with a laser light and the

scattered light emitted from the particles is detected.

• Since the frequency of the scattered light is shifted from

the incident light in proportion to the speed of the particles

movement, the electrophoretic mobility of the particles can

be measured from the frequency shift (Doppler shift) of the

scattered light.

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Cont..

• Electroacoustic phenomena: The electroacoustic

technique characterizes the dynamic mobility of particles

in colloidal systems.

• In this method, a high frequency electric field is applied

to the samples, causing charged particles to oscillate, and

to produce a sound wave of the same frequency.

• The oscillation (dynamic mobility) of the particles is

described by its magnitude and phase angle. The sound

wave is detected and analysed to determine the motion of

the particles.

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DLVO Theory

• The scientists Derjaguin, Landau, Verwey and Overbeek

developed a theory in the 1940s which dealt with the stability

of colloidal systems.

• DVLO theory suggests that, the stability of a colloidal system

is determined by the sum of the vander Waals attractive (VA)

and electrical double layer repulsive (VR) forces that exist

between particles as they approach each other due to the

Brownian motion they are undergoing.

• The vander waal forces depend on chemical nature and size of

particle. The electrostatic repulsive forces depend on density,

surface charge and thickness of double layer.12

Methods for stabilizing colloids

Stability can be obtained by surrounding colloidal particle with:

-an electrical double layer (electrostatic or charge stabilization).

-adsorbed or chemically attached polymeric molecules (steric

stabilization).

-free polymer in the dispersion medium (depletion stabilization).

•The stabilization due to the adsorbed layers on the dispersed

particle is generally called steric stabilization.

•Steric stabilization of colloidal particles is

achieved by attaching (grafting or

chemisorption) macromolecules to the

surfaces of the particles. 13

Cont..The best steric stabilizers are amphiphilic 2-block or graft copolymers.

Depletion stabilization of colloidal particles is imparted by macromolecules that are free in solution.

The study of this type of stabilization is

still in its initial stage.

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Importance

• Zeta potential governs the degree of repulsion between

the adjacent ions of like charges. Hence it is used to

predict the particle-particle interaction

• Zeta potential can be used to predict the monodispersity

(or agglomeration) of particles.

• Zeta potential can be used to study nanoparticle-cell

interactions.

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Case study

• Y. Zhang , C. S. Ozkan et.al demonstrated the use of

surface Zeta potential measurements as a new tool to

investigate the interactions of iron oxide nanoparticles

and cow pea mosaic virus (CPMV) nanoparticles with

human normal breast epithelial cells (MCF10A) and cancer

breast epithelial cells (MCF7).

• After MCF7 and MCF10A cells were incubated

respectively with two types of nanoparticles, the

significant differences in their surface charge change

indicate the potential role of Zeta potential.16

Cont..

• 50 μg/ml iron oxide and CPMV nanoparticles were incubated

with MCF7 cancer breast epithelial cells and MCF10A normal

breast epithelial cells separately in 25 cm2 flask at 37°C in a

humidified and 5% CO2 atmosphere for specified time periods

of 30 min, 4 and 24h.

• After the incubation procedure, cells were washed with

Dulbecco’s Phosphate Buffered Saline (DPBS) for three times.

MCF10A cells were lifted off using Typsin-EDTA and MCF 7

cells were lifted off using Cell dissociation buffer. After that,

they were pelleted down and suspended into Hepes buffer for

Zeta potential measurements.17

Cont..

time MCF10 A

incubated with

iron oxide

nanoparticles

MCF10 A

incubated with

CPMV

nanoparticles

MCF 7

incubated with

iron oxide

nanoparticles

MCF 7

incubated with

CPMV

nanoparticles

30min −30.47±0.15

mV

−29.93±0.88

mV

−25.17±0.52

mV

−24.51±0.73

mV

4hr −28.05±0.91

mV

−29.31±0.28

mV

−24.63±0.67

mV

−25.44±0.31

mV

24hr −27.05

mV±0.47

−25.49

mV±2.11

−26.55±0.78

mV

−26.29±

0.46 mV

ZETA POTENTIAL

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Conclusion

• Zeta potential has long been recognized as excellent tool for

characterizing colloidal system.

• In recent years the concept of zeta potential has been applied to

areas beyond classical colloidal sciences and industrial process.

• The expanding role of zeta potential in pharmaceutical sciences is

attributable to the advance in modern instrument of zeta

potential measurement, the rapid development of colloidal drug

delivery system and emphasis on interdisciplinary basic research

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References

• CVS Subrahmanyam, Textbook of Physical Pharmaceutics.

Chapter 5: Interfacial phenomenon.2nd edition,2000.

Vallabh Prakashan publications, New Delhi.

• Yu Zhang et al., Zeta potential: a surface electrical

characteristic to probe the interaction of nanoparticles

with normal and cancer human breast epithelial cells,

Biomed Microdevices 2008; (10): 321–328.

• Soheyla Honary and Foruhe Zahir, Effect of Zeta

Potential on the Properties of Nano-Drug Delivery

Systems - A Review. Tropical Journal of Pharmaceutical

Research, April 2013; 12 (2): 255-264.20

THANK YOU

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