Abstract

The rod-shaped nanoparticles of the widespread plant pathogen tobacco mosaic virus (TMV) have been a matter of intense debatesand cutting-edge research for more than a hundred years. During the late 19th century, their behavior in filtration tests applied to theagent causing the 'plant mosaic disease' eventually led to the discrimination of viruses from bacteria.

Thereafter, they promoted thedevelopment of biophysical cornerstone techniques such as electron microscopy and ultracentrifugation. Since the 1950s, therobust, helically arranged nucleoprotein complexes consisting of a single RNA and more than 2100 identical coat protein subunitshave enabled molecular studies which have pioneered the understanding of viral replication and self-assembly, and elucidatedmajor aspects of virus–host interplay, which can lead to agronomically relevant diseases.

However, during the last decades, TMVhas acquired a new reputation as a well-defined high-yield nanotemplate with multivalent protein surfaces, allowing for an orderedhigh-density presentation of multiple active molecules or synthetic compounds. Amino acid side chains exposed on the viral coatmay be tailored genetically or biochemically to meet the demands for selective conjugation reactions, or to directly engineer novelfunctionality on TMV-derived nanosticks. The natural TMV size (length: 300 nm) in combination with functional ligands such as peptides, enzymes, dyes, drugs or inorganic materials is advantageous for applications ranging from biomedical imaging andtherapy approaches over surface enlargement of battery electrodes to the immobilization of enzymes.

TMV building blocks are alsoamenable to external control of in vitro assembly and re-organization into technically expedient new shapes or arrays, which bears aunique potential for the development of 'smart' functional 3D structures. Among those, materials designed for enzyme-based biode-tection layouts, which are routinely applied, e.g., for monitoring blood sugar concentrations, might profit particularly from the pres-ence of TMV rods:

Their surfaces were recently shown to stabilize enzymatic activities upon repeated consecutive uses and overseveral weeks. This review gives the reader a ride through strikingly diverse achievements obtained with TMV-based particles,compares them to the progress with related viruses, and focuses on latest results revealing special advantages for enzyme-basedbiosensing formats, which might be of high interest for diagnostics employing 'systems-on-a-chip'

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