HCV C protein gene is constructed into the pColdII vector and expressed in E.Coli. Then ssDNA aptamer library is constructed. HCV C protein is used to screen the nucleic acid aptamer by SELEX technology. Using the competing reaction of the target antigen, the adapter sequence, padlock probe and complementary sequence of aptamer, a highly sensitive fluorescent adapter sensor is developed based on the rolling circle replication. When there is no target antigen, the complementary sequence binds with aptamer probe instead of the padlock probe, which triggers rolling circle amplification reaction. Whereas when the aptamer binds with the target antigen, the complementary sequence hybridizes with the padlock probe. Under the action of DNA ligase, the padlock probe is further cyclized and a rolling circle amplification occurs under the action of DNA polymerase. So, it is facilitated to detect HCV in blood. By designing different aptamer sequences and related nucleic acid sequences, the sensing system can be used as a general method to detect another targets antigen.

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