Highly sensitive colorimetric aptasensor for ochratoxin A detection based on enzyme-encapsulated liposome

Highlights: • A simple, low-cost, and sensitive liposome-based colorimetric aptasensor has been developed to detect OTA. • The strategy combines advantages of the signal amplification of liposome and the high specificity and low cost of aptamer. • The signal amplification via HRP-encapsulated lipsomes can be achieved in one step without additional surfactant. • The proposed colorimetric aptasensor has been applied to detect OTA concentration in corn samples with satisfied result. - Abstract: A simple, low-cost, and sensitive liposome-based colorimetric aptasensor has been developed to detect ochratoxin A (OTA). Specifically, a dumbbell-shaped probe was designed, including magnetic beads (MBs), double-stranded DNA (dsDNA), and enzyme-encapsulated liposome. The dsDNA formed by the hybridization between OTA aptamer and its complementary probe. And the dsDNA was used to contact the MBs and the enzyme-encapsulated liposome. In the presence of OTA, the aptamer preferred to combine with OTA to form G-quadruplex, resulting in the release of the detection probe and the enzyme-encapsulated liposome. Each liposome contained a large amount of HRP. Thus, when the liposome was lysed by adding the mixed solution of 3,3′,5,5′-tetramethylbenzidine (TMB) and H₂O₂, a large number of HRP were released. HRP could catalyze the H₂O₂-mediated oxidation of TMB and hence resulted in the color change from colorless to blue with the OTA concentration varying, and this variation can be observed by naked eyes easily. The result showed that the absorption intensity at 652 nm enhanced with the increase of OTA concentration ranging from 0.05 to 2.0 ng mL⁻¹, and the limit of detection was calculated to be 0.023 ng mL⁻¹ (S/N = 3). The developed colorimetric aptasensor has been applied to detect OTA concentration in corn samples with satisfied results.