What is optical density ratio of gold nanoparticle measured for?

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Marjan Malekmohamadi

A640/A525 ratio shows the amount of nanoparticle aggregation. Also, this ratio is different in different sizes. The larger the size of the nanoparticle, the higher the peak in the wavelength region of 640. This is due to the surface plasmon resonance (SPR) properties of gold nanoparticles.

The exact number of the wavelengths is different in different studies.

I used A640/A525 in my research. some articles used A520, A670 and so on.

The absorption peak is considered at whichever wavelength has the highest amount. For AuNPs with 13nm is around 520-525. And absorption in the range of blue color is considered to be around 640.

Article µPAD-based colorimetric nanogold aptasensor for CRP and IL-6...

Issabellina D. T.

Thank you Marjan Malekmohamadi for your answer.

If the exact number of the wavelenght is different for each study, how about the standard ratio value? As in my procedure it should be between 2.9-3.4, what standard ratio value do you use? Do you have any literature about nanoparticle aggregation analysis? Im so new in this area, I need to read more to get better understanding.

Oskar Axelsson

It is a simple measure of the shape of the absorption curve. Since gold nanoparticles of different sizes have different color you can estimate size and purity from such a ratio.

I used A640/A525.

You can search colorimetric sensing by gold nanoparticles. there are a lot of articles.

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