Antibody labelling.
The optimal concentration of antibody for conjugation with colloidal gold 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).
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.
Aliquot (approximately 10 ml) 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.