Effects of dysprosium oxide nanoparticles on Escherichia coli

Abstract

There is increasing interest in the study of dysprosium oxide nanoparticles (nDy₂O₃) for biomedical applications due to their fluorescence and paramagnetic properties. However, the fate of nDy₂O₃ and their effects on natural biological systems are a growing concern. This study assessed the toxicity of nDy₂O₃ on Escherichia coli for concentrations between 0.02 and 2 mg L⁻¹, exposed to three concentrations of NaCl (8500, 850, and 85 mg L⁻¹) and three glucose concentrations (35, 70, and 140 mg L⁻¹). The ranges of these variables were selected to cover manufacturer recommendations of analytical methodologies for toxicity assessment, environmental and industrial nDy₂O₃ effluent concentrations, and metabolic activity. Two array-based toxicity techniques were used to evaluate the 27 combinations of conditions. Fluorescent dyes (Live/Dead) and respirometric assays were used to measure the undisturbed cell membrane (UCM) and remaining respiration percentage (RRP), respectively. Respirometric tests showed a higher toxic effect than Live/Dead test assays, indicating that metabolic processes are more affected than the physical structure of the cell by exposure to nDy₂O₃. After exposing the bacteria to concentrations of 2.0 mg L⁻¹ uncoated nDy₂O₃ for 2 h at 85 mg L⁻¹ NaCl and 140 mg L⁻¹ glucose, the RRP and UCM decreased to 43% and 88%, respectively. Dysprosium ion (Dy⁺³) toxicity measurement suggested that Dy⁺³ was the main contributor to the overall toxicity.