Recent Advances in DLS and DPI Dave Dolak, Malvern Instruments RAMC 2007, San Diego.
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Transcript of Recent Advances in DLS and DPI Dave Dolak, Malvern Instruments RAMC 2007, San Diego.
Backscatter Optics
Dilute Samples
Concentrated Samples
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
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)
High resolution from
chromatography separation
+
Ease of use with dynamic light
scattering
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
ThicknessRefractive index
Density
MassMolar Coverage
Volume Fraction
Sensing Waveguide
Sample Liquid
Rest of sensor chip structure including reference waveguide
~100nm
DPI offers the ability to quantify changes in the thickness and density (to the sub-Angstrom level) on the chip surface.
Sensitive to sub-Angstrom changes in size at picogram concentrations--can detect onset of crystallization at nucleation.
Sensor Surface 30ÅÅ
Lysozyme pH4 Lysozyme pH7
Sensor Surface45ÅÅ
Shape orientation, binding & conformational changes
Sensor Surface
Dual Polarization Interferometry (DPI) confirms specific binding of Biotin with Streptavidin and resulting conformational change.