Biology Reference
In-Depth Information
Whereas icosahedral VNPs are incorporated into polyelectrolyte multi-
layered arrays, rod-shaped VNPs are not stably incorporated into an
alternating array, but assemble on top of the array. Rod-shaped particles
such as M13 and TMV were found to “float” on top of the polyelectrolyte
multi-layered array; they are excluded from the array and assemble in a
highly organized structure at the interface (Steinmetz
et al
., 2008b; Yoo
et
al
., 2006).
The “floating” phenomenon can be explained by inter-diffusion of the
polyelectrolytes (see below). The first study describing this phenomenon
was with M13 and the polyelectrolytes PEI and PAA. The mechanism is
outlined in Fig. 7.21 (Yoo
., 2006).
Step 1: A supporting film of polyelectrolytes is assembled using the LbL
technique; the terminating layer is the positively charged PEI. M13
is then introduced to the system. M13 particles are negatively
charged under the conditions used, and thus bind to the positively
charged terminating PEI layer. M13 particles are randomly
distributed and highly disordered.
Step 2: A further PEI layer is added. Some M13 particles dislocate and
appear on top of the structure.
Step 3: The negatively charged PAA is added. The VNPs are covered under
the PAA layer, also described as
et al
blanketing.
Step 4: PEI is added. This again results in the dislocation of M13 and the
particles appear on top of the assembly.
Step 5: The cycles can be repeated until a desired number of PEI-PAA
layers are deposited. With every PEI layer added to the system,
M13 particles dislocate and appear on top of the array. The
diffusion process also leads to an alignment of the particles at the
interface. Eventually, a highly organized 2D array of M13 particles
is fabricated (Fig. 7.21).
The “floating” mechanism can be explained by inter-diffusion of the
polyelectrolytes (Yoo
., 2006). PEI plays a major role in the inter-
diffusion process. It diffuses under the M13 layer into the multi-layered
matrix and outwards to the virus-covered surface. The PEI inter-diffusion
results in dislocation of the M13 particles and their alignment on the surface.
The ordering of the VNPs into a 2D array is spontaneous and induced by
repulsive electrostatic interactions.
The “floating” mechanism has so far only been observed with rod-shaped
VNPs (Steinmetz
et al
., 2006). In physics, buoyancy, the
upward force of an object in a fluid, is dependent on the density of the fluid
and the density and the surface area of the object itself. The densities of
rods and icosahedrons are not significantly different. In stark contrast are
et al
., 2008b; Yoo
et al
Search WWH ::
Custom Search