Synthesis and characterization of [^110mAg]-nanoparticles with application to whole-body autoradiography of aquatic organisms

Abstract

Silver nanoparticles (AgNp) were synthesized using aqueous solution of silver nitrate ([^110mAg]NO₃) with poly(allylamine) as a reducing agent and a stabilizer of the AgNp suspension. Nanoparticles were characterized by absorption spectroscopy, particle size analysis, atomic force microscopy (AFM), and transmission (TEM) electron microscopy. Different size nanoparticles (10–30 nm and 70–90 nm) were obtained by varying the polymer concentration and reaction time. The application of [^110mAg]AgNP to environmental studies, using nuclear techniques such as in vivo gamma counting and whole-body autoradiography, is demonstrated and discussed.

Introduction

The synthesis and environmental behaviour of noble metal nanoparticles (Np) has been subject of numerous publications (Wiley et al., 2007, Borm et al., 2006, Skrabalak et al., 2008). Nanoparticles can enter environmental compartments via accidental discharges, improper disposal of waste products and degradation of domestic materials containing nanodevices (Handy et al., 2008). Among metal Np, silver nanoparticles (AgNp) are exploited for their antibacterial properties and are thus widely used in cosmetics, food packaging, household products, and textiles. In the last few years, AgNp became subject of major concerns in aquatic nanotoxicology (Farré et al., 2009) as it turns out to be a very difficult task to monitor these particles in the aquatic environment and assess their effects in aquatic organisms (Domingos et al., 2009). There is an urgent need to develop innovative methods to monitor and quantify AgNp in aquatic environmental compartments and to study their fate in aquatic organisms.

Radiotracers and associated nuclear techniques, such as whole-body autoradiography and in vivo gamma counting, have been used for many years to study the fate of dissolved and dietary metals and organometals in aquatic organisms (Rouleau et al., 1999, Rouleau et al., 2000, Rouleau et al., 2001, Rouleau et al., 2006). Whole-body autoradiography allows tracking a radioactive isotope in all organs and tissues of a whole animal (up to 45 cm in length) whereas in vivo gamma counting takes advantage of the penetrating nature of γ-rays as it allows repeated non-invasive measurements of whole-body radioactivity over time that are needed to quantify uptake and elimination kinetics in living organisms.

Radioactive nanoparticles can be obtained via either de novo synthesis (Nair and Laurencin, 2008) or by neutron activation of manufactured metal nanoparticles (Oughton et al., 2008) Though neutron activation potentially allows to work with all types of manufactured metallic nanomaterials; the specific activity achieved (0.02–1.5 MBq mg⁻¹ Np) may not be high enough for studies at concentrations relevant to the marine environment (i.e.,<10^–6 g L⁻¹). De novo synthesis from commercially available [^110mAg]AgNO₃ (>20 MBq mg⁻¹ Ag) would yield AgNp with a much higher specific activity. Our aim was to synthesize and characterize radiolabelled [^110mAg]AgNp that would freely disperse in natural seawater for use in laboratory experiments and to demonstrate their usefulness for whole-body autoradiography and in vivo gamma counting using a marine bivalve, the Icelandic scallop (Chlamys islandica).