2. Experimental Section
2. 1. Preparation of Silver Nanoparticles
The silver nanoparticles used in this study were
prepared by chemical reduction of silver compounds,
following a method used by Link et al. (1999) with a minor
modification. 0.0043 g silver nitrate (AgNO3, from SigmaAldrich,
ACS reagent) was dissolved in 95 mL de-ionised
water (Millipore, 18 MΩ-cm). The resulting solution was
heated by a hot plate to boiling point whereupon 5 mL of
sodium citrate (1% w/v, from BDH Chemicals) was added.
The solution was then refluxed for 30 minutes and turned
into the AgNP suspension. After the suspension temperature
decreased to room temperature, it was stored in the dark at
4-8 0C before use. AgNPs produced by this method were
found to have a lateral size in the range of 5-35 nm,
determined from the images from a high resolution
transmission electron microscope (HRTEM) (JEOL 2100F
FGETEM) at Durham University.
2. 2. Preparation of Sea Urchin Specimens
Sperm and eggs (Gametes) were collected from adult sea
urchins (Paracentrotus lividus) inhabiting the Adriatic Sea at
Limski kanal, Croatia. Fertilization, using 0.5 M KCl injection
to induce spawning of gametes, was carried out in natural
seawater filtered through a 0.22 µm membrane filter. For
AgNP-exposed samples (in contrast to the control), about 2 h
after fertilization, AgNPs were added to the sea urchin larvae
at a concentration of 0.3 mg/L. In both cases, the larvae were
collected at 51 h after fertilization by fixing with 100%
ethanol. The samples were washed with DI water several
times before any measurements.
2. 3. XANES and FTIR
XANES and FTIR measurements were performed at
beamline ID21 of the European Synchrotron Radiation
Facility (ESRF), Grenoble, France. XANES spectra were
collected in fluorescence mode on selected points of the
sample with the beam size of 0.2 µm x 0.8 µm. Measurements
were made using X-rays with tuneable energy in the range
from 3.32 to 3.47 keV, with a 0.225 eV energy step and 0.1 s
dwell time.
FTIR spectra were collected in transmission mode, with
a resolution of 4 cm-1. The beam size was 6 µm x 6 µm,
imprinting on specimens deposited on 0.2 mm thickness BaF2
windows. Specimens were scanned with steps of 4 µm in both
directions. For each spectrum, 64 scans were accumulated
from 4000 to 500 cm-1 and averaged. Background spectra
were collected every 30 minutes.