Explore the lower size limit of a dynamic light scattering instrument

Confirming the Lower Size Specification of the Zetasizer APS

Abstract

In this application note, the measurements are done using a Zetasizer Automated Plate Sampler (APS) to demonstrate that its lower size limit is equivalent to the Malvern Panalytical Zetasizer Nano S.

Introduction

To explore the lower size limit of a dynamic light scattering (DLS) instrument, a suitable small, well defined particle or molecule that produces enough excess scattering needs to be used. Traceable latex standards are only available down to 20nm in diameter. Proteins such as lysozyme are often used as test samples for sizes below 10nm. However, for sizes less than a nanometer, there are no proteins available. Sucrose is an ideal candidate to test the performance of a light scattering system as it is small, easily obtained, available in a crystalline, pure form and readily dissolves in water. A sucrose molecule consists of a glucose joined to a fructose molecule via a linker and has a molecular weight of 342.3 Da.

A previous study measured the size of sucrose solutions using DLS [1]. These measurements were made on a Zetasizer Nano S instrument and proved that subnanometer sizes were possible by DLS. The diffusion coefficients and subsequent sizes obtained corresponded well with known structural data as well as diffusion coefficients of sucrose measured by other techniques [2,3]. In this application note, the measurements are repeated on a Zetasizer Automated Plate Sampler (APS) to demonstrate that its lower size limit is equivalent to the Zetasizer Nano S. The Zetasizer APS is a DLS instrument that automates the measurements of samples from industry standard 96 or 384 well plates.