I am using ~ 400 nm polystyrene nanoparticles, and I would like to use very diluted particle solutions for my experiments (atto-Molar range and lower). After my experimental procedure, I would like to characterize the particle size/ charge with Dynamic light scattering. So I was wondering what is the lowest concentration that DLS can detect?
Thank you in advance,
Rami
Hi Rami,
Dynamic light scattering technique is a very sensitive technique. Dilute solutions are usually preferred for this analysis to reduce multiple scattering effect. The lowest concentration DLS can detect is a function of the DLS equipment, nature of sample, optical properties, size, and optical configuration. I would suggest preparing various concentrations of your samples and monitor for consistency in the data obtained. Some DLS equipments can detect as low as 0.1 ppm concentration.
Rami Yazbeck What does "atto-molar" correspond to as particle concentration (e.g., number of particles per milliliter?)
Hello Rami Yazbeck
if you have a Zetasizer, there is a sensitivity estimator tool available in the software. Depending on the optical configuration (i.e. model) for backscattering you should be able to detect to about E8 particles / mL for sizing.
You may find this of interest: https://www.materials-talks.com/can-i-use-dls-for-xyz/
PS: attomolar = 10^(-18)mol/L = 10^(-21)mol/mL =~6*10^2/mL =~E3 part/mL is far too dilute for DLS
My question re attomolar was because it's ambiguous. Is it "moles of particles" or "molar equivalents of styrene monomer" etc. A rather unusual way to express particle concentration.
Likely 'nr fluctuations' will be most important lower limit. For reliable sizing and applicability of standard DLS theory, a sufficient number of particles in the scattering volume is needed to limit relative fluctuations in the number of scatterers contributing to the signal. Typically for>100 particles in the scattering volume this 'nr fluctuation' effect can be safely ignored, which translates to: max diameter~ 0.3 x (particle volume fraction x Vscat)^(1/3)
John Francis Miller, sorry for the confusion here. 1 attoMolar = 1*10^-18 moles/L ≃ 600 particles/mL
Hi Ulf Nobbmann and Rut Besseling
Thank you for your answers and suggestions they are really helpful. I have used NanoBrook Omni from Brookhaven Instruments to test my sample in order to answer my question. The lowest I could detect was +E06 particle/mL which is in line with your answers. Any solution below E6 particle/mL gave incorrect sizing.
Best,
Rami
Hi Rami Yazbeck Good to know that the calculator is working :)
As Rut Besseling indicated number fluctuations are the more significant lower limit in your scenario, and that turns out to be ~ 1.5E5 for the Zetasizer and ~100 particles in the scattering volume. The Zetasizer in backscattering probably has a higher scattering volume than your system if you measured at 90 degrees scattering angle. https://www.materials-talks.com/scattering-volume-in-dynamic-light-scattering-how-to-find-it/
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