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Recent Advances in DLS and DPI. Dave Dolak, Malvern Instruments RAMC 2007, San Diego. Classical vs. Backscatter Dynamic Light Scattering (DLS). Backscatter Optics.

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Recent Advances in DLS and DPI

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recent advances in dls and dpi

Recent Advances in DLS and DPI

Dave Dolak, Malvern Instruments

RAMC 2007, San Diego

backscatter optics
Backscatter Optics

Backscatter optics facilitate a variable cell position, accommodating both high & low concentration samples. The increased scattering volume ensures high sensitivity, without compromising the working size range or needing to resort to high power lasers which can lead to thermal convection.

Scattering Volumes

Concentrated Samples

Dilute Samples

advantages of backscatter optics in the zetasizer nano instrument
Advantages of backscatter optics in the Zetasizer Nano instrument
  • Broad concentration range preserves original sample conditions (“Does my sample actually change at lower concentrations?”)
  • Expanded size range (0.6nm - 6um)
  • Enhanced sensitivity yet can handle high concentrations and low concentrations without user intervention/sample prep.
  • Ease of sample preparation
    • Reduced dust problems: dust/large aggregates scatter light more in the 90-degree and forward direction. (Dust and large aggregates “hosed” 90-degree DLS rendering count rate too variable for measurement.) No so at 173º.
    • No sample filtration required!
recent advance size and mw from absolute size exclusion chromatography asec
Recent advance: Size and MW from Absolute Size Exclusion Chromatography (ASEC)

High resolution from chromatography separation+

Ease of use with dynamic light scattering

dpi technology overview
DPI technology overview

DPI stacks two waveguides together--separated by a spacer – which yields an interference pattern at the end of the waveguides. If one waveguide is used as the experimental surface, then changes in the interference pattern can be analyzed to deduce what is happening at the adsorbed layer when various materials are adsorbed to it or as those adsorbed materials change.

dpi return

Sample Liquid

Sensing Waveguide

Rest of sensor chip structure including reference waveguide

DPI Return

DPI offers the ability to quantify changes in the thickness and density (to the sub-Angstrom level) on the chip surface.

  • Thickness
  • Refractive index
  • Density
  • Mass
  • Molar Coverage
  • Volume Fraction


Sensitive to sub-Angstrom changes in size at picogram concentrations--can detect onset of crystallization at nucleation.


Lysozyme pH4

Lysozyme pH7

Sensor Surface



Sensor Surface

Sensor Surface

Shape orientation, binding & conformational changes

Dual Polarization Interferometry (DPI) confirms specific binding of Biotin with Streptavidin and resulting conformational change.

the truth is out there

The Truth Is Out There

DLS and DPI offer new insights into macromolecular behavior.