I am performing DLS (Malvern ZetaSizer Nano)experiment for 100uM protein of MW 14.2KDa, pI4.4 dissolved in 20mM Glycine NaOH buffer pH7.4. Samples have been filtered, passed through 100KDa amicon ultra filters and degassed to get low molecular weight species of 3-8 d.nm. However, I am constantly getting error that measurement cannot be performed. I have tried with increasing and decreasing the protein concentration.
Have you verified that the instrument is working correctly with a standard?
Is it possible you are losing the protein on the filter? Sometimes you have to "prime" the filter with sufficient quantity of the sample you want to measure.
Is it possible the protein is adhering to your sample cuvette?
I have performed with other samples and the instrument is working fine.
Have you looked at the raw count rate (Tools/Count Rate Meter)?
If you have the Nano Z or ZS (not the 90 variants), you can select the different detection angles (13 or 173 degrees). You can also change the attenuator setting. See attached screen shot.
You can also view the laser beam in the sample if you are using a standard cuvette and don't have electrodes inserted. Open the lid and depress the interlock with a plastic object (e.g., a pen top). See photo - interlock is where my hand is. If the scattering is very weak even with no attenuation, you may not see the beam even in a dark room.
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