<em>In situ</em> formation of magnetite nanoparticles inside pores of protein crystals

Abstract

Nanoparticles of magnetite have many biomedical applications: magnetic cell separation, DNA extraction, magnetic resonance, hyperthermia therapy, etc. Many of these properties depend of the particle size; therefore, methods able to control particle size are needed1. Magnetotactic bacteria, like Magnetospirillum strains are able to produce magnetite crystals inside their magnetosomes with a perfect shape and size considered the ideal magnetic nanoparticle.2 The particular and specie-specific morphologies of those magnetosomes are still not well understood, and some authors have pointed, as one of the possible cause, the confined space in which those crystals are produced. Crystallization in confinement occurs in a different manner compared to crystallization in bulk. During it, is possible to stabilize and study metastable polymorphs, to form crystals with preferred orientations, to modify morphologies, size and shape of crystals.3 To study the formation of magnetite crystals in a confined space we have created cross-linked protein crystals and used them as a matrix to promote the magnetite formation. Protein crystals are highly porous materials with a defined pore size that depends on the type of protein. In this work we have used two proteins (lysozyme and lipase), that have very different pore sizes. Our preliminary data show the formation of small iron nanoparticles inside of both protein crystals and confirm penetration and accumulation of iron ions inside the protein crystals. Further studies will give more information about the role of protein crystals in the formation of magnetite nanoparticles.