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 it can assess the size and the size distribution of particles and molecules in solution  within minutes using Dynamic Light Scattering (DLS). If samples are not stable, results will not be consistent or repeatable (the Expert Advice tab would flag this in the trend analysis). However, DLS may then 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 three 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, change the ‘Number of measurements’ in the measurement settings, to perform several repeated runs.  For example, 80 runs of two minutes each. The ‘Delay between measurements (seconds)’ is an optional pause between the repeated runs. As a best practice, enable the ‘Partial results’ option to save all correlation functions, even if they are not “nice quality” results.

For fast kinetics (~seconds): flow mode

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

Example on the right: data acquisition for a continuous 15 minutes, where each correlation function takes 3 seconds (every 3 seconds).

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

For ultimate flexibility, combine the above two methods with the help of the SOP Player. The SOP Player allows concatenation of several SOPs (standard operating procedures) in a row. Further options are pauses (“Pause Playlist”), temperature changes (“Set Temperature”), titration additions (“Inject Titrant”), and pH changes (“Go to pH”). This could be beneficial when looking at 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. You can access the SOP Player from the main software menu Measure – SOP Player. Below are two example situations of how you could implement the SOP Player.

For variable reactions (~minutes to ~hours): SOP Player

The SOP Player provides the most flexibility for designing your experiment. Below are two examples for the design capabilities in the Playlist. On the left, the SOP Player list contains repeat measurements for 4 times, with 1h waits in between, and then a longer wait of 24 hours before the final measurement.

You can also put several different SOPs together and turn them into an SOP Playlist [Measure-SOP Player] . On the left is an example of 4 runs with one hour (60*60sec) pause in between, and then a final measurement after 24h (24*60*60sec). You first create an SOP for the simple measurements (with the correct cuvette, dispersant, temperature, etc. conditions) and then use that SOP in the playlist with “Wait” statements in between.  Click on the Actions to add the SOP or the wait statement. You can also Copy (Ctrl-C) and Paste (Ctrl-V) on the left side, if it is the same Action, or move the order of actions in the list.   The screen on the right illustrates a single SOP for 24 times in a row, with a wait of 1 hour in between each repeat.

           

You can select statements into the playlist from the “Actions” tab. Access and change specific details about the action with the “Properties” tab, for whatever action is highlighted.

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.