The purified IgG was diluted to a concentration of 0.1mg/ml in sodium phosphate buffer
(0.001M, pH7.0). The pH of colloidal gold solution and the diluted IgG was adjusted to pH8.0 with 0.1M Na2CO3.
Ten aliquots of variable concentrations (0.01 - 0.1mg/ml) of the diluted IgG were prepared in 0.2 ml sodium phosphate buffer, and added separately to 1 ml of the colloidal-gold solution, as described previously (Li et al., 2013).
After incubating the mixture for 10 min, 0.1 ml of 10% NaCl was added to the tubes and the absorbance was mea-
sured 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