hi. gold nanoparticles can form plasmonic clusters (aggregates of nanoparticles) which are revealed through a plasmon resonance signal at 540 nm. beyond clusterize, nanoparticles should also be larger than 5 nm to display plasmonic traits. hpoing this could be useful!

Di you have peaks at other wavelengths or is there no absorbance at all?

Agree with Steven - it would be helpful if you could post the spectrum that you obtained for your solution!

Thanks Mr Ardini

color of my gold nanoparticles are very undertone pink and some articles mentioned that pink ones are more smallest than other. then your idea about size of nanoparticles may be correct. then how can i improve their spectrum?

They are very stable and اhave been not  percipitated 6 month after purification.

Mr Bell

in some of them yes and some one no.

blue,red, green shows 3 of them

ok. i suggest you to see this review. pag 312 could be helpful. good luck!

"Gold Nanoparticles: Assembly, Supramolecular Chemistry, Quantum-Size-Related Properties, and Applications toward Biology, Catalysis, and Nanotechnology"

Marie-Christine Daniel and Didier Astruc

In synthesis of Au nanoparticles with plant extract we have seen that the plasmonic peak at 520-560 nm depends on the concentration of the extract and increasing the bioreductant can help in the aggregation of the particles Please see for example "Biosynthesis of gold nanoparticles using Salvia

Officinalis leaf extract and its microbiological activity

Mostafa M.H. Khalil*, Dina Y. Sabry, Amal S.A. Khidr International Journal of Green and

Herbal Chemistry 2014, Vol.3, No.4, 1668-1678.

Hi Mansureh,

Or your nanoparticles are really small (below 3nm) or they should show a band above 500nm. In the former case the color is not red or purple but generally brown (the color of a CTAB seed solution for example). Which size do you expect to obtain? In your question you mentioned a purification step; does the color changes during or after the purification? Another option for the UV-vis analysis would be to concentrate the sample, but I think that the easiest option would be to analyze your particles by TEM.

Cheers

Hi Mansureh,

Sometimes you may not get  elevated peaks due to low concentration of nanoparticles in the medium. And one more doubt, regarding your purification process, did you treated with any other solvents, which may also interfere with your peaks. We had a similar pattern, when we reduced the concentration of nanoparticles, though we confirm the particles using TEM with EDX.  

All the best.

I agree with Balak, may be you can take the uv measurement before the purification step. Also, if you said that the colour was purple, means they are large particles and possibly may aggregate and so not be in solution again to be detected.

The color of my nanoparticles are bright pink not purple 

I studied nanoparticles spectrum after and before purification and there was no peak.

and purification step had no effect on nanoparticles color.

I am waiting for DLS result to determine  nanoparticles size.