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Abstract
A simple and feasible homogeneous electrochemical sensing protocol was developed for
the detection of ochratoxin A (OTA) in foodstuff on the immobilization-free aptamer-graphene
oxide nanosheets coupling with DNase I-based cycling signal amplification. Thionine-labeled
OTA aptamers were attached to the surface of nanosheets because of the strong noncovalent
binding of graphene oxide nanosheets with nucleobases and aromatic compounds. The
electronic signal was acquired via negatively charged screen-printed carbon electrode
(SPCE) toward free thionine molecules. Initially, the formed thionine-aptamer/graphene
nanocomposites were suspended in the detection solution and far away from the electrode,
thereby resulting in a weak electronic signal. Upon addition of target OTA, the analyte
reacted with the aptamer and caused the dissociation of thionine-aptamer from the
graphene oxide nanosheets. The newly formed thionine-aptamer/OTA could be readily
cleaved by DNase I and released target OTA, which could retrigger thionine-aptamer/graphene
nanocomposites with target recycling to generate numerous free thionine molecules.
Free thionine molecules were captured by negatively charged SPCE, each of which could
produce an electrochemical signal within the applied potentials. Under optimal conditions,
graphene-based aptasensing platform could exhibit good electrochemical responses for
the detection of OTA at a concentration as low as 5.6pg/mL. The reproducibility, precision
and selectivity of the system were acceptable. Importantly, the method accuracy was
comparable with commercialized OTA ELISA kit when using for quantitative monitoring
of contaminated wheat samples.