Biosynthesis and applications of iron oxide nanocomposites synthesized by recombinant Escherichia coli.

Recombinant Escherichia coli (E. coli) strain that produces phytochelatin (PC) and/or metallothionein (MT) can synthesize various metal nanoparticles (NPs) by reducing metal ions. Here we report in vivo biosynthesis of iron oxide nanocomposites (NCs) using recombinant E. coli. We designed a strategy of biosynthesizing iron oxide NCs by first internalizing chemically synthesized iron oxide NPs, followed by the reduction of added metal ions on the surface of internalized NPs by PC and/or MT in E. coli. For this, chemically synthesized FeO NPs were internalized by recombinant E. coli, and then, Au and Ag ions were added for the biosynthesis of AuFeO and AgFeO NCs, respectively. The NCs synthesized were analyzed by transmission electron microscopy, UV-vis spectrophotometry, and X-ray diffractometry to characterize their shape, optical property, and crystallinity. The FeO NPs in the biosynthesized NCs allowed easy purification of the biosynthesized NCs by applying a magnetic field. The AuFeO NCs were used for enzyme-linked immunosorbent assay to detect prostate-specific antigen protein, while AgFeO NCs were utilized for the antimicrobial application with low minimum inhibitory concentration. As recombinant E. coli can uptake and reduce various NPs and metal ions, biosynthesis of a wide range of NCs as new nanomaterials will be possible for diverse applications. KEY POINTS: • AuFeO and AgFeO nanocomposites were synthesized by recombinant E. coli. • Escherichia coli synthesized different iron oxide NCs depending on the metal ions to be added. • Biosynthesized AuFeO NC was used for ELISA and AgFeO NC for antimicrobial tests.