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A bifunctional aptamer-based electrochemical biosensor for label-free
detection of thrombin and adenosine has been developed. It was based on the
principle of switching structures of aptamers from DNA/DNA duplex to
DNA/target complex upon target addition. Thrombin aptamer was firstly
immobilized on gold electrode surface by self-assembly, and then it was
hybridized with adenosine aptamer. Methylene blue (MB), as an
electrochemical indicator, was abundantly adsorbed on the aptamers via
specific interaction of MB with guanine base. In the presence of thrombin
or adenosine, the aptamer part could bind with thrombin or adenosine
instead of MB. The decreased peak current of MB was intimately related to
the concentration of thrombin or adenosine. In present work, the assay was
linear in the ranges from 6 to 60nM for thrombin and from 10 to 1000nM for
adenosine. Detection limits were determined to be 3nM for thrombin and 10nM
for adenosine, respectively. Moreover, bovine plasma albumin (BSA) and
lysozyme, or uridine and guanosine, did not influence performance of the
biosensor, indicating good selectivity of this sensor for thrombin or
adenosine detection. Finally, this sensor was successfully applied to
thrombin and adenosine analysis in human plasma samples.
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