So, you’re thinking of using light scattering instrumentation?
More and more scientists are realizing that characterizing polymers and biopolymers (and particles, too!) with a multiangle light scattering instrument is the only practical way to determine absolute molar masses, sizes, and conformations without making assumptions. Light scattering is currently being used in applications including vaccine characterization and monoclonal antibody characterization. Users could be doing anything from measuring protein–protein interactions as part of drug discovery to using macromolecular engineering to produce high-performance bionanocomposites for use as silicon alternatives in breast implants!
Our scientists invented the first commercial light scattering instruments incorporating lasers as their light source more than 40 years ago. We hope this post will help to demystify the subject and make multiangle light scattering a routine part of your laboratory analysis. But first…
What is light scattering?
Only a very small amount of the light that enters our eyes does so directly from its source. We obtain virtually all of the visual information about our surroundings from light that has been scattered. We identify and differentiate objects by making deductions from the differences and quantity of light scattered from them. Even the physical properties of microscopic particles and molecules can be deduced from the measurement of the light they scatter.
Static and dynamic: What’s the difference?
In static light scattering, the scattered light intensity is measured as a function of the angle between the detector and the incident beam direction. The measurements typically average the light intensity over a time of several hundredths to several tenths of a second. Information on the molar mass, molecular root mean square radius, conformation, and intermolecular interactions can be obtained.
In dynamic light scattering (DLS), light intensity fluctuations taking place at microsecond or millisecond scales are measured. Those fluctuations are a measure of the diffusion constant (Brownian motion) of the molecules and are related to the hydrodynamic radius of a molecule.
So, if I were advising you on purchasing a laser light scattering instrument, what would I consider? Here are five questions I would ask:
1. What technical expertise and support are available from the manufacturer?
This is undoubtedly the most important question of all. As with any particular discipline, light scattering has its own lore and its own experts. If light scattering is new to you, your "learning curve" will be accelerated significantly when you purchase your instrument from the most knowledgeable people in the field. Technical support, guidance, and direction from a company whose leadership in light scattering is world-renowned mean you will be successful with your measurements and their interpretation. Building a practical light scattering instrument requires years of experience and technical qualifications. Intelligent circuit board design, state-of-the-art electronic components, superior knowledge of photodetection equipment—not to mention expertise in optical engineering and software development—all play critical roles in building exceptional and versatile light scattering instruments.
2. How many angles are measured?
The importance of the number of angles cannot be overemphasized and is critical, since it determines the precision of the measurement. More angles mean more data are collected; more data mean greater accuracy. Indeed, the precision of a light scattering measurement is roughly proportional to the square root of the number of detectors.
3. Can I clean my flow cell when it gets dirty?
As every flow cell in every light scattering instrument will eventually get dirty, the ability to quickly access and clean it is essential to ensure high throughput.
4. Is my light scattering detector really absolute?
It is preferable for instruments to measure molar mass directly from the scattered light intensity, without reference to a standard "known" molar mass. This removes the need for regular calibration, saving time and improving accuracy.
5. How stable is the light source?
Most solid-state lasers include power output monitors that can be used to ensure beam power stability; however, with age or temperature fluctuations, such lasers are prone to "mode-hopping." This degrades their stability.
To learn more, you can check out our Ultimate Light Scattering Guide by visiting http://www.wyatt.com/ or ask me a question on Twitter@WyattTechnology.
Geofrey Wyatt is President, Wyatt Technology Corp. (Santa Barbara, CA).