The optimal concentration of antibody was determined by titrating aliquots of diluted IgG with colloidal gold.
The purified IgG was diluted to a concentration of 0.1 mg/ml in sodium phosphate buffer (1 mM, pH 7.0).
Ten aliquots of variable concentrations 0.01-0.1 mg/ml of the diluted IgG were prepared in 0.2 ml sodium phosphate buffer.
After incubating the mixture for 10 min, 0.1 ml of 10% NaCl was added to the tubes and the absorbance was measured at 520 nm.
The least amount of protein required to stabilize the colloidal gold was identified from the abscissa in the curve drawn from the concentration and the absorbance.
Aliquot of purified IgG (0.1 mg/ml) was added drop-wise to l00 ml of colloidal-gold solution (pH 8.0) followed by the addition of 10 ml of filtered 10% bovine serum albumin (BSA), pH 8.0 with gentle stirring for 20-25 min.The solution was incubated for 10 min at 25°C and centrifuged at 15,000 g for 30 min at 4°C.