The trace detection of Hg2+ by flexible electrochemical biosensor based on covalent organic framework synergistic amplified strategy

Abstract

Mercury (II) ion (Hg2+) is highly toxic, which is harmful to the environment and human health. Hg2+ electrochemical detection method lacks high sensitivity and convenience. Thus, we fabricated a new-style flexible sandwich biosensor for ultra-sensitive identification of trace mercury ions in water. A large number of gold nanoparticles (AuNPs) were electrodeposited on the flexible electrode as the sensing interface, and the Au-functionalized covalent organic framework (COF) nanocomposites adsorbed a large amount of methylene blue (MB) were used as the signal amplifier. COF/Au provided a large specific surface area, which was easier to assemble with mercaptan functionalized capture DNAs (cDNA) aptamers via S-Au bonds for selective recognition of mercury, to improve the conductivity and electrochemical performance. Meanwhile, gold nanoparticles (AuNPs), MB and reporter DNA (rDNA) were anchored to COF to fabricate the COF/Au/MB/rDNA probe. The prepared COF based probe exhibited a large surface area, excellent electrical signal response, and good environmental compatibility. After incubation with Hg2+, rDNA was tightly bound to cDNA via thymidine-Hg2+-thymine pairing (T-Hg2+-T). Thus, the COF based probe was specifically connected to the flexible interface to generate electrical signals. Experimental results indicated that the biosensor exhibited wider linear response range of 0.1 pM to 100 nM Hg2+, and lower detection limit of 45.2 fM (3σ/k). In addition, the prepared ligand sensor also showed reliable detection performance in real water samples.