THE ROLE OF ATOMIC FORCE MICROSCOPY IN ADVANCING DIATOM RESEARCH INTO THE NANOTECHNOLOGY ERA - Life at the Nanoscale: Atomic Force Microscopy of Live Cells - page 404

good indication that in this case the acid treatment did not modify the true,
smooth silica outer surface. Since these studies, relatively few diatoms had
similarly been characterized until a recent survey of 16 diatom species was
undertaken by imaging all the major cell wall components (valves, girdle
bands and setae) using AFM. 18 The main conclusion from this study was
that diatom nanoscale silica structure is highly diverse between species,
within a single species, and even within a single frustule component ( Fig.
19.3a - f ) . This provided an indication that no direct correlation necessarily
exists between the nanoscale silica morphology and the frustule component
that contains it. The authors also summarized that at the mesoscale level
(deined as intermediate structures between the nanoscale and microscale),
the prevalence of linear structures, even within different frustule
components (e.g. girdle bands), suggested that an organization of linear
organic molecules or subcellular features play a conserved role in templating
structure formation on that scale.
In addition to nanoscale silica structures on the proximal and distal
surfaces, there is great interest in understanding the structural details and
composition embedded within the siliciied structures, as this may shed
more light on the principal nanostructures, or proposed organic template,
involved in biomineralization and silica deposition. A very innovative
sample design was speciically developed for this purpose so that the cross-
sectional nanostructure of the frustule could be observed. 19 The method
involved attaching a single chemically cleaned diatom to an optical ibre by
embedding the cell in a bead of epoxy resin. The ibre was then cleaved at
the mid-region of the frustule, and then threaded vertically into an aperture
holder with the cleaved face of the frustule positioned upwards for imaging.
High-resolution images of frustules

cleaved in cross-section revealed the presence of individual silica particles
in the valves and girdle bands ranging from 30 to 50 nm in diameter ( Fig.
19.3g,h ) .

P. viridis and Hantzschia amphioxys

Statistical analysis revealed no signiicant difference in particle
size from major structures (i.e. girdle bands and valves) within a frustule,
indicating for the irst time that these nanoparticles represented the primary
silica building blocks of a fully constructed cell wall.

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In particular, this
highlighted that a formless silica structure of the frustule, typically perceived
from the smooth proximal and distal valve and girdle surfaces, was in fact
composed of individual particles. A signiicant difference observed between
species indicated a species-speciic dependence and was mentioned to
relect differences in organic molecules embedded within the silica, such as
long chain polyamines and silafins, proposed to play a regulatory role in
silica polymerization.

13

The study also reported nanoscale silica particles in
the frustules of other species, including

12

Sureilla , Neidium and Pleurosigma .