In this work, the Paracentrotus lividus sea urchin is
chosen as the biological model system, and we present the
first reported study of AgNPs therein. We used synchrotron
radiation as X-ray source in the measurement, for a number
of reasons: it provides much higher intensity than
conventional X-ray tubes (resulting in reduced measurement
time) and it offers tuneability of the X-ray energy with high
collimation (Ide-Ektessabi, 2007), useful for X-ray absorption
near edge structure (XANES) spectroscopy to be undertaken
in micro-analyical mode. XANES was used to prove the
presence and distribution of agglomerated AgNPs which
were detected via X-ray fluorescence. When the incident Xray
has an energy equal to that of the binding energy of a
core-level electron, there is a sharp rise in absorption. By
varying the X-ray energy, the peak of absorbance obviously
rises at a particular energy, referred as absorption edge. The
exact position of an X-ray core-level absorption edge depends
on the chemical environment of an element such as oxidation
state, site symmetry, ligands and the nature of bonding (West,
1999). Therefore, XANES is a useful technique for
discriminating between Ag present within AgNPs, and its
presence in other chemical bonding environments within the
sea urchin larva. To complement the XANES work, infrared
light from the synchrotron was also used for Fourier
transform infrared (FTIR) micro-spectroscopy, which can
detect the vibrational bands of functional groups of
compounds (Robinson et al., 2005). With the FTIR
measurements made in raster-scan mode, several compounds
within sea urchin larva can be mapped and characterized in
order to compare the chemical change in the skeleton
between AgNP-exposed and control samples.