Shaken Not Stirred: Magnetic Viruses for Biomagnetic Sensing

Magnetic nanoparticles coated with biochemical surfactants have emerged as an important component for enabling many biological and medical applications. A general challenge in the fabrication of these nanoparticles is to generate a high degree of uniformity both in the magnetic and biochemical properties of the nanoparticles. We address this issue through biological templating of inorganic nanoparticles, which offers promising opportunities for realizing the full potential of self-assembled materials. We implemented such biotemplating to create magnetic nanoparticles by utilizing native protein capsid shells derived in high yield from T7 bacteriophage viruses.The magnetic nanoparticles are grown inside of hollowed-out capsids that retain their original chemical recognition properties. The resultant "magnetic viruses" are uniform in geometry, physical properties, and biochemical functionality. We first coax the DNA out of the T7 virus by means of an alkaline treatment, and then grow cobalt or ironoxide particles inside the remaining hollow capsid shell. The advantage of our approach is twofold: (i) the use of native virus capsids allows for a straight-forward and economical production of the magnetic nanoparticles in large quantities, which enables practical applications, and (ii) given the richness of protein types that form the native T7 capsid, our magnetic virus can be tailored via phage display libraries to tune the bio-functionality and/or bio-tagging of a sample. Thus in our approach the biological functionality of the particles is established first before the magnetism is subsequently added. This is in contrast to the traditional fabrication of bio-functionalized magnetic nanoparticles, where the particles are typically functionalized after the preparation of the magnetic particles.