Option 1: Use a fluorescein derivative with thiol attached to it. Thiol groups have a strong affinity to gold, they bind to gold nanoparticles readily.

Option 2: If you don't want to use a thiol derivative then you will need some group (e.g. -COOH, -NH2 etc) on gold nanoparticles where fluorescein can be attached to. For example, if your gold nanoparticles have a -NH2 group then commercially available FITC, NHS-Fluorescein can be used.

Article Gold Nanoparticle-Photosensitizer Conjugate Based Photodynam...

Thanks Ravi. With option 1, the gold salt is already synthesized using glutathione. so i need to conjugate fluorescein to the synthesized gold nanoparticle.

If your gold salt already has a glutathione attached to it and if you have a fluorescein derivative with thiol group then both of them could be covalently linked via a disulfide bridge.

If the -NH2 group in glutathione present on gold nanoparticles is free and is not sterically hindered then you could attach the dye by reaction with FITC.

Thank You Ravi. My interest is on the second part. How do i go about this please?

You could buy commercially available FITC conjugation kits from any one of these companies (e.g. Sigma-Aldrich, Thermofisher. Merck etc) and perform the reaction. These kits come with the protocols and other useful details.

Okay.. Thanks very much

@V.N. Ravi Kishore V. , i had FITC from a colleagues laboratory and had no protocol. Please do you have any idea how i can conjugate FITC to gold nanoparticles capped with glutathione? The conditions needed.

My supervisor disagreed me using FITC. She wants me to use an organic dye having a carboxylic group which can be activated to form an amide bond gold nanoparticles capped with glutathione.

Joseph，

Use Fam NHS ester （mixture: 5/6 Fam NHS ester is cheaper, single isomers 5 Fam NHS and 6-Fam NHS cost more），thay are activated form of FAM.

Thanks Guobing. But my supervisor doesnt want already activated organic dye. She wants me to do the activation myself so i dont think she will agree with the already activated FAM.

Then you can use Fam and do the activation/conjugation by one step!

Thanks Guobing, but my supervisor recommends fluorescein dye or Rhodamine B dye. Can there be any help for activativating this dye?

Fam is fluorescein dye , fluorescein itself does not have COOH for conjugation.

Do a search for conjugation of dye with COOH onto solid surface with NH2 , there should be many ways!

Thanks Guobing. I have sent you a private message. Please check for me.