This study offers new insights into dysprosium oxide nanoparticles (nDy2O3) exposure on E. coli with respect to its metabolic activity and structural integrity. The toxicity of nDy2O3 was evaluated for two array-based techniques, Live/Dead and respirometric assays. Our work is novel since new nDy2O3 toxicity data was produced covering manufacturer recommendations for toxicity assessments, environmental and industrial nDy2O3 effluent concentrations and metabolic activity. This is highly relevant to the evaluation of the toxic effect of nanoparticles since the physicochemical properties of the nanoparticles can differ greatly depending of the physicochemical characteristics of the aqueous solution. With an understanding of the nanoparticles fate in aqueous media, a careful selection of appropriate toxicological methodologies can be made to improve the accuracy of future nanotoxicological studies. There is increasing interest in the study of dysprosium oxide nanoparticles (nDy2O3) for biomedical applications due to their fluorescent 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, exposed to three concentrations of NaCl (8,500; 850 and 85 mg/L) and three glucose concentrations (35, 70, 140 mg/L). 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 uncoated nDy2O3 for 2 hrs at 85 mg/L of NaCl and 140 mg/L of glucose, the RRP and UCM decreased to 43% and 88%, respectively. Dysprosium ions (Dy +3 ) toxicity measurement suggested that Dy +3 was the main contributor to the overall toxicity.

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