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 Fe₃O₄ NPs were internalized by recombinant E. coli, and then, Au and Ag ions were added for the biosynthesis of AuFe₃O₄ and AgFe₃O₄ 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 Fe₃O₄ NPs in the biosynthesized NCs allowed easy purification of the biosynthesized NCs by applying a magnetic field. The AuFe₃O₄ NCs were used for enzyme-linked immunosorbent assay to detect prostate-specific antigen protein, while AgFe₃O₄ 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: • AuFe₃O₄ and AgFe₃O₄ nanocomposites were synthesized by recombinant E. coli. • Escherichia coli synthesized different iron oxide NCs depending on the metal ions to be added. • Biosynthesized AuFe₃O₄ NC was used for ELISA and AgFe₃O₄ NC for antimicrobial tests.