The virus particle has attractive features as materials, for example, homogenous size, specific modifications of particle surface via genetic and chemical manipulations, and self-amplification via its own genetic information. These properties make researchers try to develop biomaterials, sensor and scaffolds based on phage. Detection by immuno-PCR exhibits high sensitivity, but it usually requires a complex manufacturing process especially for protein-DNA conjugates. We anticipated that a genetically modified M13 bacteriophage can be used as a detection molecule in immuno-PCR. In this study, we have developed a novel bacteriophage particle which displays Z domain, an IgG binding protein, at the pIII coat proteins. The virus particle has not only a template for PCR but also a binding capability to IgG; thus the new sensing reagent can be used for immune-PCR directly by itself. The cTnI myocardial infarction marker is chosen for the demonstration of an immuno-PCR assay method using the modified bacteriophage. An initially developed immuno-PCR method showed a limit of detection as 0.092 ng cTnI/mL, which is about 4-fold lower than an ELISA method. In order to improve the platform, we are applying the site-specific modification strategies using unnatural amino acids by incorporating the analogues into the pIII and/or pVIII coat proteins. For an example, we are developing a simple method to conjugate IgG to the Z domain-displayed phage particle via a light-mediated reaction.
