Efficient removal of ethidium bromide from aqueous solution by using DNA-loaded Fe₃O₄ nanoparticles

Ethidium bromide (EtBr) is widely used as DNA-staining dyes for the detection of nucleic acids in laboratories and known to be powerful mutagens and carcinogens. In the present paper, the removal of EtBr from aqueous solutions in a batch system using DNA-loaded Fe₃O₄ nanoparticles as a simple and efficient method was investigated. DNA was covalently loaded on the surface of Fe₃O₄ magnetic nanoparticles, which was confirmed by FT-IR analysis and zeta potential measurements. The morphology and crystal structure were characterized by SEM, TEM, and XRD. The influence factors on the removal efficiency such as initial EtBr concentration, contact time, adsorbent dose, pH, and temperature were also studied. The removal process of EtBr can be completed quickly within 1 min. The removal efficiency was more than 99% while the EtBr concentration was routinely used (0.5 mg L^-1) in biology laboratories and the dosages of nanoparticles were 1 g L^-1. For the different EtBr concentrations from 0.5 to 10 mg L^-1 in aqueous solution, the goal of optimized removal was achieved by adjusting the dosage of DNA-loaded Fe₃O₄ nanoparticles. The optimum pH was around 7 and the operational temperature from 4 to 35 °C was appropriate. Kinetic studies confirmed that the adsorption followed second-order reaction kinetics. Thermodynamic data revealed that the process was spontaneous and exothermic. The adsorption of EtBr on DNA-loaded Fe₃O₄ nanoparticles fitted well with the Freundlich isotherm model. These results indicated that DNA-loaded Fe₃O₄ nanoparticles are a promising adsorbent for highly efficient removal of EtBr from aqueous solution in practice.