An electrochemiluminescence biosensor for sensitive and selective detection of Hg2+ based on π–π interaction between nucleotides and ferrocene–graphene nanosheets

A solid-state electrochemiluminescence (ECL) biosensor based on a DNA-modified electrode platform that depends on the variation of π–π interaction before and after the binding of target analytes is put forward. The single-stranded DNA (ssDNA) probe was successfully assembled on the surface of a glassy carbon electrode (GCE), which was pre-modified with Ru(bpy)32+ complex and gold nanoparticles (GNPs). The ssDNA probe could strongly adsorb graphene due to the strong π–π interaction between nucleotides and graphene (GN), while in the presence of Hg2+, the conformational transformation of DNA from a single-stranded to a double-stranded structure resulted in inhibited adsorption of GN. With thymine (T)-rich ssDNA as a Hg2+ probe, we prepared the ECL biosensor by using ferrocene–graphene (Fc–GN) as a quenching unit to quench the ECL emission of Ru(bpy)32+, and the Hg2+ can be detected by quenching efficiency transformation when the Fc–GN gets away from Ru(bpy)32+. The biosensor exhibited a sensitive response to various ranges of concentration of Hg2+ with a detection limit of 18 pM. The ECL biosensor held great promise in the highly sensitive and selective detection of Hg2+ in natural water.