Nico:

Thank you for your two cents.

Best regards.

There are potentially two different questions and set of answers here depending on whether you wish to compare multi-angle DLS with single-angle DLS, or with NIBS in particular.

NIBS is more than a simple single angle back scatter detection set up. The use of a variable measurement position means that measurements can be optimised to reduce sensitivity to scattering from the cell wall by measuring in the cell centre, but when samples of high concentration are measured, and multiple scattering is detected (when high scattering but low correlation intercept) is observed, the measurement position can be optimised to nearer the cell wall to reduce the effects of multiple scattering.

The same can not be said for other arrangements where a single angle is used, and some of the concerns raised above by Nico may still stand.

Another advantage of NIBS over other single angle detection arrangements, such as 90 degree detection, is lower sensitivity to aggregates, which will preferentially scatter in forward directions, and also higher probe volume based on the cross over area of the NIBS and incident beam, when compared with detection beams at other angles.

Whether a single angle or multiple angles are used, dust and aggregates may still be identified by analysis of the correlation function, but Malvern do have instruments that detect both using NIBS and forward angle detection, meaning that the presence of any large size components can be accurately observed.

In terms of dealing with sample concentration, I am a little confused by some of Nico's comments. There is nothing to stop a DLS instrument performing intensity measurements for a series of sample dilutions for measurement of kD, second virial coefficient and molecular weight, through generation of a Debye plot. This is in fact one of the measurement procedures supported by the Malvern Zetasizer. 

Regards

Dear Yuri,

as we often do not expect what is going to happen next year, I would suggest that in Russia it is better to keep in mind all the possibilities, so the multi-angle DLS is better option in my opinion. We work with AuNP with Horiba SZ-100 DLS device which provides 90 or 173 degree detection, and we badly need more angles.

If the maintenance is not a problem, you can check the Russia-produced "Photocor Complex" - it can be built with a variety of detectors and automation options, including the motorized goniometer.

Best regards, Andrei.

Dear Colleagues:

We discussed the problem for simple sample: solid nanoparticles, polymers. It would be interesting to consider the problem for more complex systems:  concentration fluctuations + density fluctuations of water, spinodal decomposition, oscillatory system.

Best regards.

In my opnion DLS at one angle can provide highly reliable data, however there are limitations: specifically, when interactions, struture factor, form factor or rotational diffusion are the focus of the investigation, then multiple angle goniometer data will be necessary. For a wide range of applications (comparing batch to batch, grow to a certain size, study aggregation versus time or temperature,...) the single angle approach has made DLS a more accessible technique than goniometer based data acquisition http://www.materials-talks.com/blog/2016/01/12/how-do-dls-size-results-differ-with-angle/