Aggregation-kinetics

“I’m looking to study the aggregation kinetics of my nanoparticles using the Zetasizer Nano ZS.

Is there a way to make time-resolved size measurements using this instrument?”

The Zetasizer has become a fairly standard sizing tool for nanoparticles, as the size and the size distribution of particles and molecules in solution can be assessed within minutes using Dynamic Light Scattering (DLS). If samples are not stable, results will not be consistent or repeatable (which would be flagged by the trend analysis within the Expert Advice tab); however, DLS can then be used to provide insight into the aggregation kinetics of the reaction or the dynamics of agglomeration. Processes such as particle or fibril formation as well as oligomerization may be elucidated using light scattering.  There are two different modes in the software to accomplish this.

For slow reactions (~minutes): time trends

Kinetics-DLS-standardIf the reaction is fairly slow (~minutes) a size trend measurement is a simple way to investigate aggregation kinetics. Here, it is possible to specify a particular duration for each measurement. In a standard size measurement, the ‘Number of measurements’ should be changed in the measurement settings, so that several repeated runs are assessed.  For example, 80 runs of two minutes each.

For fast kinetics (~seconds): flow mode

If the reaction is faster (~seconds) then the flow measurement mode could be utilized. Kinetics-DLS-fastThis is a special continuous acquisition mode designed for chromatography, that can also be used in normal, non-flowing samples.

Example: data acquisition for a continuous 15 minutes, where a correlation function is taken every 3 seconds.

Note: to obtain the individual correlation functions once the measurement is completed, use the flow macro export facility.

For ultimate flexibility, the above two methods can be combined with the help of the SOP Player, which allows concatenation of several SOPs (standard operating procedures) in a row, with added availability of pauses (“Pause Playlist”), temperature changes (“Set Temperature”), titration additions (“Inject Titrant”), and pH changes (“Go to pH”). This could be beneficial when looking very slow kinetics, or studying stability over time, temperature, buffer conditions, etc.  We recommend the simple SOP approach at first, then use of the SOP Player for additional flexibility in experiment design.

Previously

If you have any questions, please email me at ulf.nobbmann@malvern.com. Thanks! While opinions expressed are generally those of the author, some parts may have been modified by our editorial team.