Husham N Noori Please provide more detail. By "optical examinations", do you mean microscopy, light scattering? Or do you mean liquid formulations put on the eye during eye tests?

Does "liquid nanoparticles" mean emulsion? Or do you mean nanoparticles dispersed in a liquid.

Hello Doctor John Francis Miller, I mean by optical properties like Uv-vis and PL. Nanoparticles prepared in solvent

Husham N Noori First, make sure your dilution is done in a liquid with the same composition of any salts, surfactants etc.

My approach would be:

1. Make a series of 2-fold dilutions of your sample and measure the UV-vis absorbance of each. Plot the absorbance as a function of dilution and look for a linear region on the graph.

2. Select a dilution that is roughly in the middle of the linear range.

I do not have experience with PL measurements but I suspect a similar approach would help.

Thank you very much, Doctor John Francis Miller, for the clarification. My problem is that an absorption peak does not appear. By examining more than one sample, I see a decrease in wavelength values instead of going towards larger wavelengths. I am currently using deionized water, how can I determine the percentage of dilution when writing the law.

Husham N Noori

Dilution in DI water is about the worst thing you can do for nanosystems as it is likely that you destabilize the original material. Read John Francis Miller 's first sentence again: make sure your dilution is done in a liquid with the same composition of any salts, surfactants etc' and carry out this advice. This identical composition continuous phase is called the 'mother liquor'.

In the international standards for many techniques a concentration ladder is recommended in order to understand the system and remove possible artefacts (e.g. multiple scattering or particle-particle interactions in light scattering)