  We report on the construction of multiarm colloidal molecules by tip-linking
filamentous bacteriophages, functionalized either by biological engineering or
chemical conjugation. The affinity for streptavidin of a genetically modified
vector phage displaying Strep-tags fused to one end of the viral particle is
measured by determining the dissociation constant, Kd. In order to improve both
the colloidal stability and the efficiency of the self-assembly process, a
biotinylation protocol having a chemical yield higher than 90% is presented to
regioselectively functionalize the cystein residues located at one end of the
bacteriophages. For both viral systems, a theoretical comparison is performed
by developing a quantitative model of the self-assembly and interaction of the
modified viruses with streptavidin compounds, which accurately accounts for our
experimental results. Multiarm colloidal structures of different valencies are
then produced by conjugation of these tip-functionalized viruses with
streptavidin activated nanoparticles. We succeed to form stable virus based
colloidal molecules, whose number of arms, called valency, is solely controlled
by tuning the molar excess. Thanks to a fluorescent labeling of the viral arms,
the dynamics of such systems is also presented in real time by fluorescence
microscopy.
