Magnetic beads based colorimetric detection of mercuric ion

A simple and sensitive DNAzyme-based colorimetric sensor for detecting Hg 2+ based on T–Hg 2+ -T base pair and magnetic beads (MBs) is proposed. In the presence of Hg 2+ , capture probes (CPs) immobilized on MBs are hybridized with the signal probes (SPs) consisting of G-quadruplex sequences with the help of T–Hg 2+ -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 H 2 O 2 -mediated oxidation of ABTS to produce a blue-green-colored product. A linear relationship between the absorbance and Hg 2+ concentration is observed over a range of 10–200   nM with a limit of detection 5   nM. Taking advantage of MBs separation/collection process, the sensing system can be regenerated by using EDTA as the chelator.