Studies on the uptake and transformation of gold(iii) and gold nanoparticles in a water–green algae environment using mass spectrometry techniques

Abstract

Interactions of Au(III) and citrate-stabilized gold nanoparticles (AuNPs) of different nominal diameters (10, 20 and 40 nm) with green microalgae Desmodesmus subspicatus were studied. Both inductively coupled plasma mass spectrometry (ICP MS) and high performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (HPLC-ICP MS) were applied to measure total gold content and AuNP size, respectively. After 24 h exposure of algae to gold species at environmentally relevant concentration, quantitative uptake was observed for Au(III), whereas for AuNPs it was size dependent and increased with increasing particle size. It was found that the surface water matrix has no significant influence on the cell-associated amount of gold as the uptake was comparable for algae suspended in Milli-Q and surface water. To characterise the transformations of gold species in aquatic environments, hydrodynamic diameters of AuNPs in surface water, algal cells and supernatants were determined. Gold species were extracted from algal cells using an optimized ultrasound assisted extraction procedure. The accuracy of size determination was evaluated by analysis of NIST Reference Material 8011 (10 nm AuNPs). Cellular localization and core diameter determinations of AuNPs were performed by transmission electron microscopy (TEM). It was found that the introduction of Au(III) into algal cultures leads to intracellular localization of AuNPs (6–7 nm). The 10, 20 and 40 nm AuNPs did not penetrate inside cells; however, their hydrodynamic size increased after the incubation test due to the formation of a biocorona. The thickness of the biomolecule corona was calculated and it depended on particle size. Despite the observed uptake and transformations of gold species, no effect on algal growth was noticed during the 24 h incubation period at the studied exposure concentration.