Synthesis of dispersive iron or iron–silver nanoparticles on engineered capsid pVIII of M13 virus with electronegative terminal peptides

M13 is a filamentous Escherichia coli virus covered with five types of capsid proteins, in which pVIII with ~2700 copies was around the cylindered surface and pIII with five copies located at one end of the phage particle. The pIII-engineered M13 phages with enhanced binding specificity toward Fe were screened after five rounds of biopanning, and the one containing ATPTVAMSLSPL peptide at pIII-terminus was selected for mediated synthesis of zero valent (ZV) Fe nanoparticles (NPs) with the wild M13 as control. Under a reducing environment, uniformly dispersed ZVFeNPs with diameter of 5–10 nm were both synthesized and the morphologies after annealing were confirmed to be face-centered cubic type. The synthesized FeNPs mediated by the two phages showed no significant difference, revealing that the pVIII capsid did dominant contribution to metal binding in comparison with the pIII. A novel pVIII-engineered M13 containing AAEEEDPAK at terminus, named as 4ED-pVIII-M13, was constructed and it carried one more negatively charged residue than the wild one (AEGDDPAK). Metal adsorption quantification showed that the binding affinity of the 4ED-pVIII-M13 toward Ag and Ni ions improved to 62 and 18 % from original 21 and 6 %, respectively. The binding affinity toward Fe remained constant (~85 %). ZVFe–Ag bi-NPs were successfully synthesized through mediation of 4ED-pVIII-M13. Particularly, the Fe:Ag ratio in the bi-NPs was conveniently controlled through changing the molar concentration of FeCl2 and AgNO3 solution before reduction.