Abstract
Four different manufactured surface-coated silver nanoparticles (AgNPs) with coating of citrate, tannic acid, polyethylene glycol, and branched polyethylenimine were used in this study. The toxicity of surface-coated AgNPs was evaluated by a luminous microbial array for toxicity risk assessment (LumiMARA) using multi-species of luminescent bacteria. The salt stability of four different AgNPs was measured by UV absorbance at 400 nm wavelength, and different surface-charged AgNPs in combination with bacteria were observed using scanning electron microscopy (SEM). Both branched polyethylenimine (BPEI)-AgNPs and polyethylene glycol (PEG)-AgNPs were shown to be stable with 2% NaCl (non-aggregation), whereas both citrate (Cit)-AgNPs and tannic acid (Tan)-AgNPs rapidly aggregated in 2% NaCl solution. The values of the 50% effective concentration (EC50) for BPEI-AgNPs in marine bacteria strains (1.57 to 5.19 mg/L) were lower than those for the other surface-coated AgNPs (i.e., Cit-AgNPs, Tan-AgNPs, and PEG-AgNPs). It appears that the toxicity of AgNPs could be activated by the interaction of positively charged AgNPs with the negatively charged bacterial cell wall from the results of LumiMARA. LumiMARA for toxicity screening has advantageous compared to a single-species bioassay and is applicable for environmental samples as displaying ranges of assessment results.
Highlights
Bioassays using bacteria for toxicity screening have been applied widely as acute toxicity bioassays to understand the ecotoxicological impact of pollutants on aquatic organisms [1,2] due to their advantages in simplicity, rapidity, cost-efficiency, and reproducibility [2,3,4,5]
The values of the 50% effective concentration (EC50) for bioluminescent bacteria exposed to four different AgNPs were measured following the manufacturer’s protocol using Luminous microbial assay for toxicity risk assessment (LumiMARA) system (NCIMB Ltd., Bucksburn, Aberdeen, UK), including
The aggregation of Cit-AgNPs and tannic acid (Tan)-AgNPs in 2% NaCl solution was clearly verified by Scanning Electron Microscopy (SEM) images (Figure 2A,B), whereas the morphological shapes of polyethylene glycol (PEG)-AgNPs and branched polyethylenimine (BPEI)-AgNPs were only slightly changed in the same solution (Figure 2C,D)
Summary
Bioassays using bacteria for toxicity screening have been applied widely as acute toxicity bioassays to understand the ecotoxicological impact of pollutants on aquatic organisms [1,2] due to their advantages in simplicity, rapidity, cost-efficiency, and reproducibility [2,3,4,5]. The microbial assay for toxicity risk assessment (MARA) has recently been developed for the ecotoxicological assessment of chemical and environmental samples [6,7]. MARA, a multi-species assay, uses 11 varying microbial strains that show different sensitivities to different chemicals This results in the array producing 11 inhibition values indicative of biological toxicity for the tested chemicals or samples [6,7,8]. This assay has some advantageous compared to the other microbiotests for the initial assessment of toxicity for a number of chemicals and environmental samples at various sensitivity ranges [7]
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