The simplest procedure for physical adsorption of IgG on colloidal gold is as follows:
Before the conjugation with colloidal gold, the antibodies were dialyzed against a 1000-fold excess of 10 mM Tris-HCl buffer, рН 8.5, for 2 h at 4°C. Then 0.2 М K2СО3 was added to the colloidal gold solution (D520=1.0) until pH 8.5 was reached, and the antibody solution was spiked at a desired concentration. The mixture was incubated with stirring at 20-22°C 30 min, and then BSA was added to a final concentration of 0.25%. The colloidal gold particles with immobilized antibodies were separated from unbound antibodies by centrifugation at 8,000 g for 30 min. After the removal of the supernatant, the precipitate was resuspended in Tris-HCl buffer containing 0.25% BSA. If long-term storage of the product was necessary, NaN3 was added to the final concentration of 0.02%.
You can find detailed protocols in "Bioconjugate Techniques" (https://www.amazon.com/Bioconjugate-Techniques-Third-Greg-Hermanson/dp/0123822394). Even older editions will be sufficient and may be available in 2nd hand books sites (e.g. www.abebooks.com).
I have the 1st edition (1996) and it is perfectly OK for usual use. You can generate the colloid yourself from gold chloride, which is very economical (a small amount of gold will generate liters of colloid), or you can buy colloids ready from different suppliers (Google them) and they will provide suitable protocols.
Did you ever look at www.innovabiosciences.com? Their conjugation kits are great and very easy to use.
The simplest procedure for physical adsorption of IgG on colloidal gold is as follows:
Before the conjugation with colloidal gold, the antibodies were dialyzed against a 1000-fold excess of 10 mM Tris-HCl buffer, рН 8.5, for 2 h at 4°C. Then 0.2 М K2СО3 was added to the colloidal gold solution (D520=1.0) until pH 8.5 was reached, and the antibody solution was spiked at a desired concentration. The mixture was incubated with stirring at 20-22°C 30 min, and then BSA was added to a final concentration of 0.25%. The colloidal gold particles with immobilized antibodies were separated from unbound antibodies by centrifugation at 8,000 g for 30 min. After the removal of the supernatant, the precipitate was resuspended in Tris-HCl buffer containing 0.25% BSA. If long-term storage of the product was necessary, NaN3 was added to the final concentration of 0.02%.
Optimum pH for conjugation will always varies, we have to identify the optimum pH, concentration of gold and concentration of antibodies by separate experiment.
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