Hi Niazul,

You can look into the following articles, where thiolated-PEG was anchored at different densities on gold nanoparticles. Using similar methods from [1 and 2], you could experimentally calculate maximum grafting density for your aptamers. I suppose quantification of unbound aptamers will be much easier compared to the quantification of PEG.

An extract from article [1]: "This saturation is apparent at a PEG addition rate of 16.8 μg/ml with a maximum PEG loading achievable of ∼14 wt.%. This corresponds to approximately 1,140 thiol-terminated PEG molecules per AuNP giving a chain density of 1.13 chains/nm2 (assuming a spherical particle 17.9 nm in diameter). This is significantly below the theoretical density for a close-packed helical layer of PEG of which is ∼5 chains/nm2 [33]".

[1] Article Polyethylene glycol functionalized gold nanoparticles: The i...

[2] Article The Effect of PEG Grafting Density and Hydrodynamic Volume o...

Reference [33] from the article [1]:

Article Terminal Attachment of Polyethylene Glycol (PEG) Chains to a...

Best Wishes.

Hi Niazul, you can probably calculate the density using perfect Au surfaces and perfect SH- aptamers.

Unfortunately, things are never perfect when it comes to actual experiments in the real world.

I have conjugated proteins/small molecules to carbon nanotubes, fluorescent particles, glass, gold, silver, quantum dots etc. and theoretical calculations are totally useless.

Optimal conjugation procedures have to be determined empirically.

Thank you.

Based on our experience, at the end, you should perform a series of experiment for different aptamer concentrations. you must check the stability of each conjugation through adding NaCl salt. Check our recent publication.

Article A cross- linking gold nanoparticles aggregation method based...