Maybe a thermal treatment could help you to agregatte de gold nanoparticles due to coalescence of them.

@ Mathias thanks, you mean i should heat the sample so as to aggregate them? do you have any idea the temp. and duration?

That question is kind of trick especially when we are talking about nanoparticles were the chem/phys properties changes a lot when compared to the bulk. It is know that gold nanoparticles have different mobility and melting point than bulk gold, and these properties are related to size.

I am thinking something around 400°C for 1h. Be sure that you glass doesn´t melt at this temperature...

Thinking a little bit more about your question is it possible to do a more concentrated gold NPs solutions so that you have more gold nanoparticles to interact one with the other?

Is it possible to do more depositions over the glass?

Well th eanswer is yes, i have tried concentrating the gold double and also 4 times , though i get increase in plasmon peak (absorbtion )but i dont see any secondry peak for aggregation, i also tried to use some linking molecules like cysteamine and 1,8 octanedithiol as described in literature but the result is same :(

Have you performed any imaging characterization like SEM? How far are the NP from each other?

Yes we did it today ,yet to see the images...the inter particle distances are around 100-160nm it just a guess from my previous experience

Hello Mr Badri. Then you can Sonication for 1h, 2h and 3hrs in each you try zeta sizing the particles and see if there is any change. if not you can sonicate for the above hrs and you try using TEM. In sha Allah within the two methos you will get the size you need.

Also when sonicating you are to take small or very little amount of sample then you Sonicate.

@ shafiu , sorry i didnt understand your reply, can you ellaborate, i want my samples to aggregate so as to have a secondary peak and i dont want to decrease or increase the size of my particle

for defined aggregaztion, we have good experience with H2O2, or even better, withz a sum.micromoler amount of sodium phosphate buffer.

buffer is quite reliable and the principle is just sestabilisation according to DLVO theory.

of course, this works better with ligand-free nanoparticles, or at least particles that are washed.

in addition, electrodeposition offers good control over aggregation, on glass, you can do it with ITO coating or just covervthe metalkm electrode with thin glass. see:

Jakobi, J. ; Menendez-Manjon, A. ; Chakravadhanula, Venkata Sai K. ; Kienle, L. ; Wagener, P. ; BARCIKOWSKI, S.: Stoichiometry of alloy nanoparticles from laser ablation of PtIr in acetone and their electrophoretic deposition on PtIr electrodes. In: Nanotechnology 22 (2011), Nr. 14, S. 145601

and

Menendez-Manjon, A. ; Jakobi, J. ; Schwabe, K. ; Krauss, J. K. ; BARCIKOWSKI, S.: Mobility of Nanoparticles Generated by Femtosecond Laser Ablation in Liquids and Its Application to Surface Patterning. In: JLMN - Journal of Laser Micro / Nanoengineering 4 (2009), Nr. 2, S. 95–99 [OPEN ACCESS]

sorry Stephen i didnt understand your reply completely,can you elloborate?

you mean i should use hydrogen per oxide on gold coated glass surface to induce aggregation?

Sorry that my comment was not clear. In our lab (we use ligand-free gold nanoparticles in water and acetone, see

http://youtu.be/J0vZgQFDyjo ), 2 strategies work to achieve plasmon coupling of the gold nanoparticles shifting the extinction peak towards higher wavelengths:

A) Aggregation at the colloidal state:

You can use addition of salt (sub-micromolar concentration) or an oxidative reagent to aggregate the gold colloid. probably, this works better the less stabilizers are on the gold nanoparticle surface.

B) Aggegation on the surface:

Using an electric field (two electrodes dipped in your colloid) amplifies the depositon process. After a few minutes electrophoretic deposition, a dense nanoparticle coating builds up and plasmon coupling ocurs.

Good luck,

Regards,

Stephan

thanks Stephan, i saw the video, the nano particles created by laser ablation, can they form aggregates on APTES coated glass when deposited?

as i am interested in gold aggregation on glass surface , u mentioned using electrodes dipped in colloid, unfortunately we dont have that facility here yet, is there any there way to create plasmon on gold coated surface