Bio-mediated self-assembly of nanoscale structures using the M13 bacteriophage

The M13 bacteriophage is ~1 μm long, with a capsid comprised of five coat proteins.
Small peptides can be displayed upon the coat proteins. The aim of this work was to use
the phage display of small peptides for the purpose of fabricating a self-assembling
molecular transistor with the M13 bacteriophage acting as the scaffold. Each aspect of
this fabrication was considered.
Firstly, a 50 nm long microphage particle was re-created and used to produce a
215 nm long phage particle. These smaller phage particles could be used to make the
transistor 100 nm in size. To create the scaffold, selenocysteine was displayed on the
coat protein pIII and used to self-assemble two to four phage particles around 10 nm
gold nanoparticles or quantum dots. These higher order structures were then purified
using a linear sucrose gradient. So that the transistor could be directed to a specific area
of an existing electronic circuit, the coiled-coil pair ACID:BASE was used. ACID was
displayed on the coat protein pIX whilst a BASE peptide containing a Cvterminal
cysteine was immobilised onto a gold surface. It was shown that ACID and BASE form
a coiled-coil when the BASE is immobilised on a surface and that the M13
bacteriophage, displaying ACID, can be anchored to the surface via coiled-coil
formation. Finally, tyrosine was displayed on the major coat protein pVlIl so that gold
could be specifically reduced onto the M13 phage particle scaffold to create the gold
electrodes of the transistor. Although within solution, and on a carbon surface, gold was
reduced onto the phage particles, when the particles were adsorbed onto an Si02 surface
there was no gold deposition.
Therefore, although much progress was made towards the goal of a self
assembling transistor, the aspects devised within this study need to be combined.