Fluorescence Resonance Energy Transfer Aptasensor of Ochratoxin A Constructed Based on Gold Nanorods and DNA Tetrahedrons.

Ochratoxin A (OTA) contamination of corn has received significant attention due to the wide distribution and high toxicity of OTA. The maximum residue limit standard of OTA in corn has been established by the Chinese Government and other unions. Nanoparticle-based fluorescence resonance energy transfer (FRET) assays are promising methods for the sensitive and fast detection of OTA. However, satisfactory detection sensitivity is commonly achieved with complicated signal amplification processes or specific nanoparticle morphologies, which means that these assays are not conducive to fast detection. This study proposes a simple and novel strategy to improve the sensitivity of FRET aptasensors. In this strategy, a DNA tetrahedron was first used in gold nanorod-based FRET aptasensors. DNA tetrahedron-modified gold nanorods are used as fluorescent acceptors, and Cy5-modified complementary sequences of the OTA aptamer are used as fluorescent donors. The aptamers of OTA are embedded in the DNA tetrahedrons, and FRET occurs when the aptamers hybridize with the Cy5-modified complementary sequences. The aptamer-integrated DNA tetrahedron modified on the surface of gold nanorods acts as an anchor, thus avoiding the crowding and entanglement of aptamers. Due to the competitive combination between the OTA aptamers and complementary sequences, the greater the amount of OTA, the less the amount of Cy5-modified complementary sequences that bind with the aptamers and the less the amount of Cy5 that is quenched. Thus, the fluorescence intensity is positively related to the OTA concentration. In this study, in the concentration range of 0.01-10 ng/mL, the fluorescence intensity was found to be linearly related to the logarithmic concentration of OTA. The limit of detection was calculated to be 0.005 ng/mL. The specificity of the developed biosensor was demonstrated to be efficient. The accuracy and stability of the developed aptasensor were also tested, and the method exhibited good performance in real samples.