Graphene oxide (GO) and carboxylated GO were used as labels for lateral flow immunoassays, instead of the conventionally used colloidal gold and colored latex labels. A sensor is demonstrated that enables fast screening for aflatoxin B (AFB) as a model analyte using the antibody-GO complex as the recognition element. The visual limit of detection and cut-off value for AFB are 0.3 and 1ng/mL, respectively. It is shown that GO and carboxylated GO are viable black labels for use in lateral flow assays, one typical advantage being the saving cost (compared to the use of colloidal gold). Qualitative results are achieved within 15min, and the analytical results were in good agreement with the reference LC MS/MS method. The method was successfully applied to the on-site determination of AFB in agricultural products. In our perception, it opens new possibilities for the screening of other toxins by lateral flow immunoassays using GO and carboxylated GO as labels.