number of natural surfaces such as insect wings exhibit superhydrophobic and
self-cleaning properties, and therefore have potential industrial applications.
Some insect wing surfaces were recently reported to possess bactericidal
activities. In an effort to understand the mechanisms responsible for the antibacterial
effect of insect wings, a combination of advanced microscopic, spectroscopic
and chromatographic techniques, i.e., scanning electron (SEM) microscopy, Synchrotron-sourced Fourier-transform infrared
microspectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) depth
profiling and gas chromatography-mass spectrometry (GCMS), were employed to evaluate the physical and chemical
properties of the surfaces of the dragonfly Hemianax
papuensis wings (donated by Melbourne Museum). The cross-sectional view of
the wing surface revealed that the wing is comprised of three main layers.
These include two
epicuticular layers of approximately 180-200 nm thickness on the dorsal and
ventral surfaces, and an intracuticular layer of approximately 2.5 µm thickness, where the bulk membrane is located. Using GCMS, it was found that hexadecanoic
acid, octadecanoic acid and n-alkanes were the predominant components on the
outermost surface of the epicuticular layer of the wing. The location of particular
classes of compounds was determined using XPS depth profiling. The results
indicated that the hexadecanoic acid is present mostly as a thin layer (approximately
30 nm in thick) on the outer surface of the epicuticle, and also present with
octadecanoic acid within a deeper layer. Aliphatic compounds were found to be
present across the wing membrane, forming a discrete layer which appeared to be
different from that of the inner and outer layer of the epicuticle.