A competitive thrombin-linked aptamer assay for small molecule: aflatoxin B1.

We described a competitive thrombin-linked aptamer assay for small molecule, using aflatoxin B1 (AFB1) as a model, taking advantage of aptamer affinity binding and enzymatic activity of thrombin. We designed a dual functional DNA probe that contained the aptamer sequence for thrombin and the aptamer sequence for AFB1. Thrombin was labeled on the DNA probe by affinity binding between thrombin and anti-thrombin aptamer. This thrombin-labeled DNA probe was attached on AFB1-bovine serum albumin conjugate (BSA-AFB1) coated on a microplate through the affinity interaction between AFB1 and anti-AFB1 aptamer. The thrombin attached on the microplate catalyzed the cleavage of peptide substrate into detectable product, generating signal for detection. In the presence of AFB1, free AFB1 competed with BSA-AFB1 in the binding to the limited amount of DNA probe, leading to signal decrease. Detection of AFB1 was achieved by measuring the signal change. Under optimized conditions, AFB1 was successfully detected in the range from 0.5 nM to 1 μM when fluorogenic peptide substrate of thrombin and fluorescence analysis were applied. The use of chromogenic peptide substrate in the assay allowed the detection of AFB1 ranging from 0.5 to 125 nM by simple absorbance analysis. The thrombin-linked aptamer assay showed good selectivity towards AFB1, and enabled the detection of AFB1 spiked in diluted beer and corn flour. This TLAA strategy extends the analytical application of thrombin and aptamers in detection of small molecules. Graphical abstract.