Antibody-free colorimetric determination of total aflatoxins by mercury(II)-mediated aggregation of lysine-functionalized gold nanoparticles

Currently known immunoassays for aflatoxins (AFs) usually are not capable of simultaneous determination of total AFs (i.e., aflatoxin B-1, aflatoxin B-2, aflatoxin G(1), aflatoxin G(2)) due to the lack of group-specific antibodies. We are presenting here a colorimetric method for determination of total AFs by exploiting the Hg(II) ion-mediated aggregation of lysine-functionalized gold nanoparticles (Lys-AuNPs). AFs bind Hg(II) ion to form stable complexes, and this prevents the Hg(II) induced aggregation of Lys-AuNPs. Hence, the color change of solutions of AuNPs that occurs after aggregation of the AuNPs is suppressed. This effect was exploited to design a method for quantitation of AFs that can be detected by UV-Vis spectrophotometry (by measuring the ratio of absorbances at 725 nm and 525 nm), and even with bare eyes. The method has a very low detection limit (1.1 ppb) and is highly selective for AFs over other mycotoxins. Colorimetric analysis of rice samples by this method gave results that were in good agreement with those obtained by HPLC. To the best of our knowledge, this is the first method for visual detection of total AFs based on the distance-dependent optical properties of AuNPs.