For bioconjugation of citrate capped gold nanoparticles with BSA (prepared in PBS pH 7.4), I have added 200 micro liter of BSA solution to 1000 micro liter of AuNPs. But immediately after adding of BSA to AUNPs, the nanoparticle solution turned black. Why this bioconjugation procedure not working?
Any suggestions?
This depends on the concentration of BSA which is present in the PBS solution and the quality of the nanoparticles prior to the addition of the PBS. One thing to try before addition of the BSA is to triple filter the PBS to ensure that it is sterile. Presence of small ions or low salt concentrations shall cause spontaneous agglomeration of the nanoparticles as the citrate capping ligands shall be removed. What is the plasmon peak wavelength for your nanoparticle batch and have you performed sizing measurements? What concentration of BSA are you using?
As PBS contains NaCl, thus due to salt effect your gold nanoparticles turns into black color. You should prepare your BSA stock in water.
yes you have to avoid salt, salt can induce the aggregation and colour change of theses NP
How about if I convert 10X PBS (pH 7.4) to 1X PBS by adding DI water and then use it for dissolving BSA?
First, you should dllute the 10x PBS buffer before use, I mean it is 10 times concentrated than your BSA solution should be.
You change the ionic strength with this buffer with adding PO4 Na and Cl for your Gold colloid solution. It may cause aggregation of your nanoparticles. Try to add PBS to gold to see if the color changes is because of the buffer and not because of BSA.
you can prepare BSA solution in poor water too you do not need buffer for doing that.
The aggregation or the color changes could be due to PBS as well. there are many positively charged side on the surface of BSA.
Corona formation and other interaction within BSA and gold have been studied relatively well. here is an article
http://pubs.acs.org/doi/abs/10.1021/la050588t
GNP is stable in PBS with 7.4. Try to use 20-30nm particles .the larger size particles agglomerated easily. GNP concentration seems to be very high since 10 micro litre solution have more number of GNPs to bind.Match molar concentration of BSA and GNP.
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