Bifunctional fusion protein was created by genetically fusing GBP and H1a, allowing specific interactions between GBP and the gold substrates as well as the capture of H1a and its antibodies. As described in the previous report [16] , the DNA fragments encoding the H1N1 viral surface antigen (H1a) were amplified by PCR with forward primer (5′-CCATGGCATATGGG CCACCATCACCATCACCACGGCAA-3′) and reverse primer (5′-CCGCTCGAGCTGGCTACG CACTTTTTCATACAGGTTTTTAACGTTGCTATCGTGATAGCCGCAAGCTTGTCGACA-3′) for the construction of 6His-GBP-H1a fusion gene. Then, the PCR product was cloned into the NdeI-XhoI fragment of pET-6HGBP to make pET-6HGBP-H1a.