Engineered nanoparticles have been investigated for potential application of their unique physicochemical properties due to their inherent size. Gold nanoparticles have gained considerable attention for potential medicinal drug delivery, bio-imaging, and diagnostic purposes. However, research exploring the potential untoward effects of gold nanoparticles on embryonic development has yet to be explored. The objective of the present study was to evaluate dose-dependent effects of gold nanoparticles (10 nm) on embryonic development via a sea urchin model (Arbacia Punctulata and Strongylocentrotus purpuratus). It is well-established that vertebrates share specific features of embryonic development with sea urchins (both deuterosomes) and thus the sea urchin has served as a fundamental model of developmental biology for over a century. Additionally, we are able to easily evaluate effects of environmental toxicants in vitro using this model. We hypothesized that gold nanoparticles would inhibit development to the larval pluteus stage. Sea urchins were injected with two aliquots of 100-300 µl 0.5 M KCl to induce gamete release. Thereafter, 100 µl each of sperm and oocyte suspension and 800 µl of artificial seawater (ASW; pH = 8, salinity = 36, and osmolarity = 800 mOsm/kg; Instant Ocean Aquarium Systems, Inc., Mentor, OH) were added to a 1-ml center-well culture dish (Falcon, Becton-Dickinson Labware, Franklin Lakes, NJ, USA) to allow for fertilization at 25 oC in ambient air. After 90 minutes of incubation, the 1 ml of 2-cell embryo suspension was diluted to 5 ml for further use. One-hundred microliter aliquots of 2-cell embryo suspension were added to 900 µl ASW to create either negative control or treatment conditions (2.85x104 particles/ml, 2.85x107 particles/ml, and 2.85x1010 particles/ml ASW). Embryos were incubated for 2, 20, and 48 hours. At each respective time-point, the number of embryos/plutei within three fields of vision of each plate was counted under an inverted microscope (Olympus America Inc., Center Valley, PA), and the relative percentage of each respective stage/total was calculated. A Kruskal-Wallis test revealed a significant decrease in the percentage of embryos attaining pluteus stage at 48 hours in nanogold-treated versus control cultures (n=6; p<0.05). Subsequent individual Mann-Whitney U tests revealed that gold nanoparticle concentrations of 2.85x104(n=6; p<0.005) and 2.85x1010(n=6; p<0.02) gold particles/ml ASW significantly inhibited development to pluteus stage relative to control. However, 2.85x107 particles/ml ASW (n=6; p = 0.055) did not significantly decrease development at 48 hours. These results suggest that gold nanoparticles can inhibit development to pluteus stage in A. punctulata and S. purpuratus. No other significant effects of gold nanoparticles on embryonic development (i.e., 2-cell through blastulae) were observed (n=6, p>0.05). Collectively, our studies point to sea urchin embryonic development as a target of gold nanoparticle action, and our model may serve to provide routine evaluation of toxicants in aqueous environments. This research is supported in part by the University of Wisconsin-Milwaukee College of Letters and Sciences. (poster)