Bidirectional Detection of Ochratoxin A by Covalent G-Quadruplex Heme Chloride

In this work, an aptamer sensor for the specific detection of Ochratoxin A (OTA) was prepared by attaching single-stranded G-rich DNA to the OTA aptamer in order to form a G-quadruplex, followed by covalent attachment of heme chloride at the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5^{\prime } $ </tex-math></inline-formula> end through the formation of an amide bond. OTA was detected by two different modes, the first was the use of OTAS1—upon binding of heme chloride to OTA, the aptamer base in OTAS1 preferentially binds to OTA, and fewer G-quadruplexes are formed, resulting in a decrease in horseradish peroxidase activity. The second is the introduction of OTAS2. In the absence of OTA, the DNA maintains a double-stranded structure and does not form G-quadruplexes. Upon addition of OTA, the OTA binds to the aptamer, the DNA double-stranded strand is unstranded, and the G-rich part of the G-base forms G-quadruplexes, which are covalently associated with hematoxylin chloride, resulting in the formation of horseradish peroxidase. The discovery of the bidirectional detection mode provides new ideas and directions for the field of analytical detection.