BACKGROUND: Hg(II) and MeHg(I) are toxic pollutants causing wide concerns. Polyamidoamine-grafted magnetic silica nanoparticles (Fe3O4-SiO2-PAMAMs) were synthesized as beads, on which herring sperm DNA fragments were immobilized as reacting moieties for removal of Hg(II) and MeHg(I) from water matrices. The factors influencing the removal, such as DNA fragments, generation of the polyamidoamine spacers and pH, were studied. Further, the adsorption mechanisms were explored by means of adsorption kinetics and isotherms. RESULTS: Assembling DNA fragments on the polyamido amine-grafted beads promoted sharply the removal of both Hg(II) and MeHg(I). Adsorptions of Hg(II) and MeHg(I) followed pseudo-second-order kinetics; but their adsorption isotherms obeyed Langmuir and Freundlich models, respectively. Under the optimum conditions, the adsorption equilibrium time was approximately 5min for Hg(II) and 5 s for MeHg(I) with maximum percentage removals of similar to 95% and similar to 90%, respectively. The adsorbent could be regenerated easily without significant decrease in removal efficiencies. CONCLUSION: The Fe3O4-SiO2-PAMAM beads could bind DNA steadily, and the DNA fragments interacted strongly with mercury species. The strategy enabled the water-soluble DNAs to work as efficient removing reagents for rapid and cost-effective removal of Hg(II) and MeHg(I). (c) 2016 Society of Chemical Industry