Preparation of Colloidal Gold and Gold-Labeled Monoclonal Antibodies

Colloidal gold was prepared by trisodium citrate method (22). Briefly, 1 mL of 1% chloroauric acid was added to the erlenmeyer flask with 99 mL double distilled water which was stirring and heating, followed by the rapid addition of 1.6 mL of 1% trisodium citrate solution with rapid stirring. The mixture was boiled for another 5 min and gradually boiled until the color gradually changes from light yellow to deep red and no longer changes in color. The colloidal gold solution was cooled to room temperature and then stored at 4 °C.

McAbs were centrifuged at 12,000 × g for 5 min and incubated with colloidal gold solution for 30 min. Then the 10% bovine serum albumin (BSA) was added to the colloidal gold conjugation and incubated for 10 min. The mixture was then centrifuged at 12,000 × g, 4°C for 30 min to remove any unbound antibody. The pellet was resuspended in boric acid buffer containing 1% BSA.