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ELECTROPHORETIC LIGHT
SCATTERING (ELS)
K.Lohitha
 It is an analytical method that measures the electrophoretic mobility
under an applied electric field.
Principle
 Based on electrophoresis & dynamic light scattering.
 the suspension is illuminated by a light source, generally a laser of a
visible wavelength (∼400–800 nm).
 The scattered light from the suspension is sampled by an optical
system connected to a photodetector and signal processing system
that allows the measurement of particle motion utilizing the Doppler
effect.
Instrumentation
☻A laser beam passes through the electrophoresis cell, irradiates the
particles dispersed in it, and is scattered by the particles. Light scattered
by the particles is detected by a photomultiplier (PMT).
☻Use heterodyne scattering methods in which a
fraction of the laser beam is split away before reaching the
sample by a mirror and directed to the PMT detector where
it is combined with scattered light from particles diffusing in
the sample.
☻ The fraction of redirected light is referred to as the
“local oscillator” and unlike the light scattered by the sample does not
fluctuate.
☻It is used as a reference beam and must be much larger than the
average intensity of the scattered light produced by the diffusing particles.
By superposing the reference and scattered beams a frequency shift can
be obtained.
☻From the frequency (or Doppler) shift the particle velocity can be
calculated.
 The image shows a typical
ELS power spectrum
obtained for 262nnm latex
spheres under and an
electric field of 10V/cm. The
center peak is called the
reference peak with no
applied electric field.
 The sample peak is shifted -
19.3Hz which corresponds to
an electrophoretic mobility of
-3.61 M.U. and zeta potential
of -48.8 mV assuming the
Smoluchowski limit.
 The sample peak is broader
than the reference peak
indicating a range of zeta
potentials within the sample
rather than a single value.
Advantages Disadvantages
 Rapid measurement -
electrophoretic mobility of
hundreds of cells may be
measured simultaneously in a
matter of seconds.
 Highest resolution compared
to other methods
 Requires small sample volume
(0.1ml)
 Solution conditions of
physiological to very low ionic
strength can be used.
 Major disadvantage is that it is
strictly an analytical
technique,although the fine
differences in the cell mobilities
can be distinguished,the cells
cannot be physically separated
for further analysis.
Primarily used for characterizing the surface charges of colloidal
particles like macromolecules or synthetic polymers (ex. polystyrene)
in liquid media in an electric field.
In addition to information about surface charges, ELS can also
measure the particle size of proteins and determine the zeta potential
distribution.
Case studies

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Electrophoretic Light Scattering

  • 2.  It is an analytical method that measures the electrophoretic mobility under an applied electric field. Principle  Based on electrophoresis & dynamic light scattering.  the suspension is illuminated by a light source, generally a laser of a visible wavelength (∼400–800 nm).  The scattered light from the suspension is sampled by an optical system connected to a photodetector and signal processing system that allows the measurement of particle motion utilizing the Doppler effect.
  • 4. ☻A laser beam passes through the electrophoresis cell, irradiates the particles dispersed in it, and is scattered by the particles. Light scattered by the particles is detected by a photomultiplier (PMT). ☻Use heterodyne scattering methods in which a fraction of the laser beam is split away before reaching the sample by a mirror and directed to the PMT detector where it is combined with scattered light from particles diffusing in the sample. ☻ The fraction of redirected light is referred to as the “local oscillator” and unlike the light scattered by the sample does not fluctuate. ☻It is used as a reference beam and must be much larger than the average intensity of the scattered light produced by the diffusing particles. By superposing the reference and scattered beams a frequency shift can be obtained. ☻From the frequency (or Doppler) shift the particle velocity can be calculated.
  • 5.  The image shows a typical ELS power spectrum obtained for 262nnm latex spheres under and an electric field of 10V/cm. The center peak is called the reference peak with no applied electric field.  The sample peak is shifted - 19.3Hz which corresponds to an electrophoretic mobility of -3.61 M.U. and zeta potential of -48.8 mV assuming the Smoluchowski limit.  The sample peak is broader than the reference peak indicating a range of zeta potentials within the sample rather than a single value.
  • 6. Advantages Disadvantages  Rapid measurement - electrophoretic mobility of hundreds of cells may be measured simultaneously in a matter of seconds.  Highest resolution compared to other methods  Requires small sample volume (0.1ml)  Solution conditions of physiological to very low ionic strength can be used.  Major disadvantage is that it is strictly an analytical technique,although the fine differences in the cell mobilities can be distinguished,the cells cannot be physically separated for further analysis.
  • 7. Primarily used for characterizing the surface charges of colloidal particles like macromolecules or synthetic polymers (ex. polystyrene) in liquid media in an electric field. In addition to information about surface charges, ELS can also measure the particle size of proteins and determine the zeta potential distribution.