Hi,

In terms of instrument settings, I would recommend using the automatic settings and the instrument will optimise accordingly if it can.

Your count rate is very low, but the intercept is high which suggests you are mostly measuring just background Scattering but with moments of high Scattering when individual particles transit the laser beam.

Look at the quality report and follow any guidance there, but I suspect that your particles are too dilute.

A word of warning for measuring CNT via DLS- the size result generated by DLS is a diameter of a sphere that diffuses at the same rate as the particle. This will typically be inaccurate therefore for rod like particles. Anisotropic particles may also complicate the analysis if a rotational diffusion coefficient is detected.

Bearing all of that in mind, when your method is optimised and giving repeatable results, I would recommend using it for comparison between conditions and not an absolute size measurement.

As Alex indicated the size quality report might provide some hints on how to improve the data. You might find the comment in https://www.materials-talks.com/blog/2014/07/10/faq-peak-size-or-z-average-size-which-one-to-pick-in-dls/ useful.

For your sample, hydrogen peroxide could cause formation of bubbles, which would interfere with DLS (and lead to larger size contributions and number fluctuations). If your sample is still very dark, you may have to dilute it more. You could also try to force the measurement position closer to the wall. If the size is changing, measuring right after sonication could help confirm whether that is the case. https://www.materials-talks.com/blog/2016/04/21/aggregation-kinetics-with-dls/