Magnetic beads based colorimetric detection of mercuric ion

•A simple and sensitive colorimetric sensor for detecting Hg2+ was proposed.•The sensor based on the catalytic activity of hemin/G-quadruplex DNAzyme and T–Hg2+-T base pairs.•The sensor exhibited high sensitivity and high selectivity.•The sensor could be regenerated by using EDTA as the chelator. A simple and sensitive DNAzyme-based colorimetric sensor for detecting Hg2+ based on T–Hg2+-T base pair and magnetic beads (MBs) is proposed. In the presence of Hg2+, capture probes (CPs) immobilized on MBs are hybridized with the signal probes (SPs) consisting of G-quadruplex sequences with the help of T–Hg2+-T base pairs. The SPs are separated by MBs and used to bind hemin for the formation of catalytically active hemin/G-quadruplex DNAzymes, which catalyzes the H2O2-mediated oxidation of ABTS to produce a blue-green-colored product. A linear relationship between the absorbance and Hg2+ concentration is observed over a range of 10–200nM with a limit of detection 5nM. Taking advantage of MBs separation/collection process, the sensing system can be regenerated by using EDTA as the chelator.