Molecular Weight Measurement of Proteins Using Dynamic Light Scattering (DLS)

By AZoNano

Table of Contents

Introduction
Measurement Procedure
Molecular Weight Calculation
Conclusion
About Avid Nano

Introduction

According to laser light scattering theory, when the size of a molecule is much smaller than the wavelength of the incident laser light, there is very little angle dependence in the measurement. Hence, a single scattering angle can be used to accurately measure molecular weights for molecules up to about 25nm in size. The ‘Molecular Weight Calculator’ feature of i-Size software from Avid Nano takes advantage of this useful capability to measure the molecular weight of proteins and other small molecules.

The i- Size’s Molecular Weight Calculator feature is on the basis of the theory proposed by the Rayleigh equation for molecular weight measurement.

Measurement Procedure

A flow cell is positioned in the sample holder of the W130i DLS system and a series of dilutions of known concentrations is introduced into the flow cell by manual injection, starting with pure solvent followed by each sample. i-Size 2.0 software is used to record concentration and scattering intensities for each of the solutions.

Molecular Weight Calculation

The count rate and solvent refractive index calculated from a toluene reference standard as well as the sample concentrations and time averaged scattering intensities are entered into the Molecular Weight Calculator.

Figure 1. Molecular Weight Calculator in Avid Nano's i-Size software

Using these values, a Debye plot is created as shown in Figure 2, with molecular weight (Mw) and 2nd Virial Coefficient (A2) highlighted in red (Figure 1).

Figure 2. Debye plots of protein solutions and a toluene reference

Conclusion

The W130i DLS system is useful to provide accurate measurement of molecular weight of proteins in solution. It can also rapidly and precisely measure molecular size and aggregation state using unique disposable 5 µl BladeCell cuvettes from Avid Nano.

About Avid Nano

Avid Nano produce the most exciting and innovative new dynamic light scattering products. Avid Nano pursue the highest levels of performance, know-how, technology, convenience and reliability for all our products, used in laboratory applications requiring fast, accurate DLS measurements in the nano-metre size range.

The W130i dynamic light scattering system is a breakthrough, high sensitivity instrument for size and molecular weight measurement of proteins, bio- molecules and sub-micron particles. The W130i combines ultimate measurement performance with an economical benchtop footprint, rugged durability and supreme user convenience. It's extraordinarily compact dimensions are the result of miniaturized 'diamond geometry' S.A.B.Re fibre optic technology.

This information has been sourced, reviewed and adapted from materials provided by Avid Nano.

For more information on this source, please visit Avid Nano.

Date Added: Feb 12, 2013 | Updated: Jun 11, 2013
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