Fabrication of DNA-protein conjugate layer on gold-substrate and its application to immunosensor

The fabrication of antibody thin film using both protein G and oligonucleotide was carried out by self-assembly (SA) technique for immunosensor. A mixture of 11-mercaptoundecanoic acid (MUA) and oligonucleotide with thiol (SH) end group was self-assembled of gold (Au) surface for two-dimensional (2D) configuration. Protein G was chemically adsorbed on the 11-MUA surface, and then the antibody was immobilized on the protein G region. On the immobilized single-stranded DNA, the complementary DNA–antibody conjugate was hybridized for the oriented immobilization of antibody. The formation of self-assembled 11-MUA/oligonucleotide layer, protein G immobilization, antibody layer, and antigen binding was investigated using surface plasmon resonance (SPR). The topographies of the fabricated surfaces were observed by atomic force microscopy (AFM). When compared with the amount of antigen binding on the antibody thin film fabricated by protein G only, the proposed biosurface fabricated with both protein G and oligonucleotide showed better binding capacity, which implicates the improvement of the detection limit.