Utilization of aptamer-functionalized magnetic beads for highly accurate fluorescent detection of mercury (II) in environment and food

[Display omitted] •An aptamer-based fluorescence biosensor was developed for Hg2+ detection.•This assay avoids the direct binding of Hg2+ and the fluorescent signal probe.•Aptamer-functionalized magnetic beads were used to separate Hg2+ and signal probe.•The assay shows high accuracy, remarkable sensitivity and excellent selectivity. A fluorescent assay for Hg2+ was developed based on magnetic separation and the formation of T-Hg2+-T base pairs. The aptamers were immobilized on the surfaces of magnetic beads to form aptamers-functionalized magnetic beads (AMB). In the absence of Hg2+, the signal transduction probe (STP) can combine with AMB through complementary base pairing. There is almost no STP in the detection solution after magnetic separation, which results in the fluorescence signal quite weak. The presence of Hg2+ leads to the formation of T-Hg2+-T base pairs between aptamers and help DNA. After magnetic separation, Hg2+ is separated from the system and STP is left in the solution, so the fluorescence signal was significantly enhanced. The fluorescence intensity linearly increased with the increasing of Hg2+ concentration from 2 to 160nM with the detection limit of 0.2nM. This method has been successfully applied to test and quantify Hg2+ in river water and ribbon fish with satisfactory recoveries, and the results were in full agreement with those from the atomic fluorescence spectroscopy (AFS). As-built method could avoid the direct binding of Hg2+ with the fluorescent signal probe. Therefore, combining with magnetic separation, the heavy metal-fluorescence quenching effects could be effectively eliminated.