Rapid and highly sensitive detection of mercury ion (Hg2+) by magnetic beads-based electrochemiluminescence assay

A novel and highly sensitive electrochemiluminescence (ECL) assay based on magnetic beads separation/collection process and thymine-Hg2+-thymine (T-Hg2+-T) coordination chemistry has been designed to detect Hg2+ ions in aqueous solution. In this protocol, two amine-terminated complementary DNA probes with five thymine-thymine (T-T) mismatches were introduced. One was coupled with carboxyl-modified magnetic beads and the other was labeled with tris (2, 2-bipyridine) ruthenium (II) (TBR). The couple of DNA probes, in the presence of Hg2+, can form double-stranded structure via the Hg2+-mediated coordination of T-Hg2+-T base pair. Therefore, they can be collected on the surface of electrode using a magnetic field. On the electrode, TBR labels and tripropylamine (TPA) could react to emit photons, which were detected by a custom-built ECL system. The detection limit for Hg2+ in this assay is 5 nM, which is below the upper limit of Hg2+ for drinkable water mandated by United States Environmental Protection Agency (EPA), 10 nM. To the best of our knowledge, this is the first example of ECL assay applying to detect Hg2+ with highly sensitivity and selectivity.