A simple, sensitive and cost-effective method for the analysis of the mycotoxin aflatoxin B1 (AFB1) has been established based on controlled growth of immunogold. AFB1-BSA conjugate modified magnetic beads were employed as capture probe and anti-AFB1 antibody-coated gold colloids were used as detection probe for the immunological recognition of AFB1, as well as for signal transduction. The immune recognition event is converted into the gold enlargement signal which can be quantitatively measured by UV-vis spectroscopy. The autocatalytic enlargement of immunogold was conducted in aqueous solution containing chloroauric acid, hexadecyltrimethylammonium bromide and ascorbic acid. The reaction could be stopped by the addition of sodium thiosulfate. The final absorbance and resonance light scattering intensity were highly dependent on immunogold concentration. After gold enhancement, the sensitivity of the immunoassay was improved and total assay time reduced to 1 h. Under optimized conditions, the linear range and lower detection limit was 0.01-1 ng mL(-1) and 7 pg mL(-1), respectively. The proposed method offers great promise for sensitive detection of other mycotoxins and organic pollutants.