Recently, the company told me that I can get a concentration of sample, however I want to know how precise is this measurement. If it actual represents the nanoparticle concentration of my sample. I know that a series of dilutions need to be prepared to analyze by DLS. However by nanoparticles measurments are showing one sharp peak and the size is the expected one.
Using the scattering intensity from dynamic light scattering (DLS) is not usually done. Theoretically it would be possible to use the derived countrate (the intensity corrected for any reduced laser input power, this is a parameter which can be displayed in the software) to estimate the concentration of your sample. It would be necessary to have a "concentration reference standard" where the concentration was known, and where the scattering objects are exactly the same as the one in the sample. If there was such a standard, then the derived countrate is directly proportional to the concentration:
Known concentration of X g/L scatters Y kcps, the solvent alone scatters Z kcps, if the unknown concentration sample scatters U kcps then the unknown concentration would be (U-Z)/(Y-Z)*X in g/L.
In real samples, this is very difficult, because one cannot be sure that the reference set and the actual sample do have the same composition. For example, if there was some reaction or aggregation which caused the average size of your sample to be higher than the average size for your reference, then the intensity change would not only be due to a concentration change but also due to a size change. A potential way to check if the size was not changing would be to confirm with the DLS and count rate results at different concentrations. So it could be quite involved and leave many potential sources of complication. The situation may be improvable where DLS is combined with a separations technique like FFF.
If you are only working with Au or Ag nanoparticles then a simple measurement of their extinction using UV/Vis spectroscopy and using Beer Lamberts Law will give you an accurate measure of the concentration of nanoparticles within your sample.
Try to read this article:
Vysotskii V.V. , Uryupina O.Ya. , Gusel’nikova A.V. , Roldugin V. I. On the Feasibility of Determining Nanoparticle Concentration by the Dynamic Light Scattering Method// Colloid Journal. 2009. V.71, N6. P.739.
But it is only for the relative concentration, not for the absolute one (i.e. determination of concentration changes for the same sample).
Sure, both, Dispersion Technology and Colloidal Dynamics produce proper instrumenation. See their sites.
Cesar Ortiz Ledon just wanted to add to my answer from a while back. There may now be a possibility that multi-angle DLS (simultaneous analysis of correlation functions at three angles) may give improved an improved resolution size distribution that can then be used to obtain the concentration of particles in a specific peak of the distribution. This will require a reference (typically Toluene) and knowledge of the optical parameters (real and imaginary refractive index i.e. absorption) - and it will only work in a limited concentration range (single scattering)
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