Alginate-based magnetic nanosorbent immobilized with aptamer for selective and high adsorption of Hg2+ in water samples

Alginate-coated magnetic nanocluster (MNC) immobilized with Hg2+-specific aptamer was synthesized to obtain the nanosorbent with high adsorption capacity and high selectivity for trace analysis of inorganic mercury (Hg2+) in water samples. Magnetite nanoparticle was first synthesized by a co-precipitation of iron precursors in the presence of alginate to obtain alginate-coated MNC, followed by immobilization with avidin. Hg2+-Specific DNA aptamer labeled with biotin was then conjugated on the MNC surface via specific avidin–biotin interaction to form aptamer-immobilized MNC. Coating the MNC with alginate can improve its water dispersibility and also increase its adsorption capacity toward Hg2+ (350 mg/g). It exhibited high selectivity through thymine-Hg2+-thymine (T-Hg2+-T) interaction with high tolerance to other foreign ions. This nanosorbent showed linearity over the Hg2+ concentration range of 0.2–10 μg/L with a correlation coefficient of 0.9977, limit of detection of 0.46 μg/L, and enrichment factor of 13. Moreover, it also showed a potential for detection of Hg2+ in drinking and tap water samples with satisfactory recoveries.