Zeta potential

Importance of zeta potential has been widely increased in the field of pharmacy

1. Zeta Potential By T.Dilip Kumar Ms(Pharm.)Pharmaceutics NIPER,Raebareli

2. Contents Introduction. Definitions. Factors affecting. Measurement. DLVO Theory. Importance . Case study. Conclusion. References. 2

3. Introduction Zeta potential is a scientific term for electrokinetic potential in colloidal dispersions. It is usually denoted using the Greek letter zeta ( ζ), hence ζ- potential. The electric potential at the boundary of the double layer is known as the Zeta potential of the particles and has values that typically range from +100 mV to -100 mV. 3

4. 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

5. 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. 5

6. Factors affecting zeta potential 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

7. 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. 7

8. 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

9. 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( κ a)/3 η where UE = electrophoretic mobility, z = zeta potential, ε = dielectricconstant , η = viscosity and f( κ a) =Henry’s function. 9

10. 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. 10

11. 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. 11

12. 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

13. 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

14. 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. 14

15. 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. 15

16. 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

17. Cont.. 50 μ g/ml iron oxide and CPMV nanoparticles were incubated with MCF7 cancer breast epithelial cells and MCF10A normal breast epithelial cells separately in 25 cm 2 flask at 37°C in a humidified and 5% CO 2 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

18. 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 18

19. 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 19

20. References CVS Subrahmanyam , Textbook of Physical Pharmaceutics. Chapter 5: Interfacial phenomenon.2 nd 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

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