The Column - February 2009 - (Page 39)

February 2009 www.thecolumn.eu.com The Column Q&A Rapid Dynamic Light Scattering Sigrid Kuebler from Wyatt Technology talks about the DynaPro Plate Reader — an instrument capable of high throughput dynamic light scattering. Why was the DynaPro Plate Reader developed? For more than 30 years, conventional dynamic light scattering (DLS) measurements have been performed in the same, mind-numbing and labour-intensive way: standing or sitting next to an instrument for hours, manually measuring one sample after another in a single cuvette. The DynaPro Plate Reader was developed to address the growing need for rapid, automated and reliable DLS measurements. With the emergence of microarray technology for drug research and discovery it became necessary to develop equally rapid screening methods. The idea to use disposable standard 96-, 384- and 1536-well plates had been applied to other detection methods before, such as UV and fluorescence assays, but no one had ever implemented it in a DLS instrument. What is unique about this approach? The DynaPro Plate Reader is the only DLS instrument on the market that screens samples directly in microwell plates. There is no sample transfer needed, which makes it a truly non-invasive, non-perturbing experiment. Cross-contamination due to using the same cuvette for multiple samples or transferring samples is eliminated. Sample measurements can be completely automated, which makes measurements of several aliquots of the same sample, formulation buffers and repeat measurements a snap. The samples can be easily recovered or the plate can be used for further screening. The industry standard microwell plates are disposable so there is no need for cleaning the optical cell and the associated need for suitable wash liquids and a liquid waste reservoir. Contact author: E-mail: Sigrid Kuebler info@wyatt.com At the same time, it has the same sensitivity and the flexibility to act as a conventional DLS system — the user simply decides which mode the measurements should be performed in. How it works: Dynamic light scattering measures the translational diffusion of molecules in solution due to Brownian motion. As the molecules diffuse, their relative positions change with time. This causes fluctuations in the intensity of the scattered light because of interference. Small molecules diffuse quickly and generate signals that fluctuate rapidly. Conversely, large molecules generate signals that fluctuate slowly. The diffusion coefficient from these fluctuations is determined by autocorrelation analysis. If the molecule is assumed to be a uniform sphere, the Stokes-Einstein relationship enables the molecule’s hydrodynamic radius to be determined from the diffusion coefficient (see Figure 1). In the DynaPro Plate Reader the microwell plate containing the samples is automatically moved from one well to the next for each measurement. See http://www.wyatt.com/ solutions/hardware/PlateReader.cfm for a demonstration of the instrument in action. What were the main obstacles to overcome in the development of this product and how did you overcome these? When performing light-scattering measurements, care must be taken to ensure high quality of the incident and scattered light, (i.e., the optical paths need to be tightly controlled and stray light must be minimized.) At the same 39 http://www.thecolumn.eu.com http://www.wyatt.com/solutions/hardware/PlateReader.cfm http://www.wyatt.com/solutions/hardware/PlateReader.cfm

Table of Contents for the Digital Edition of The Column - February 2009

The Column - February 2009
Contents
Rapid Sample Preparation Technique for the Extraction of Dioxins and Furans from Animal Tissue and Animal Feed Using Pressurized Fluid Extraction
News
Incognito
Market Trends and Analysis
Tips and Tricks: GPC/SEC
Multi-residue Pesticide Analysis in Foods Using Modified QuEChERS Extraction and Ion Trap GC–MSn Analysis
Quantification of Protein Phosphorylation Using Chip-based LC–MS
A New Perspective on the Challenges of Mass Spectrometry
Q&A

The Column - February 2009