An ultrasensitive electrochemical sensing platform for Hg²⁺ based on a density controllable metal-organic hybrid microarray

A novel electrochemical Hg²⁺ biosensor was developed on the basis of a metal-organic hybrid microarray, in which the nicking endonuclease (NE) assisted target-triggered strand release strategy was realized via the DNA cyclic amplification technique. The metal-organic hybrid microarray was fabricated using the SAM of 1, 4-benzenendithiol as soft template, and the density of the microarray could be adjusted by controlling the surface coverage of 1,4-benzenendithiol molecules. In the presence of Hg²⁺, capture DNA (cDNA) with an indicator at one end could hybridize with the reporter DNA (rDNA) through the stable T-Hg²⁺-T linkage, forming the nicking recognition site. After the nicking reaction, the electrochemical indicator dissociated from the electrode surface. The released rDNA and Hg²⁺ could be reused in the sensing system and initiate the next cycle, and more electroactive indicator dissociated from the electrode surface, resulting in a significant signal decrease. The constructed DNA biosensor could detect Hg²⁺ in a wide linear range from 15pM to 500nM, with an ultrasensitive detection limit of 5pM (S/N=3). Furthermore, the biosensor exhibited excellent stability, good reproducibility and high selectivity towards other divalent ions. The proposed sensing system also showed a promising potential for the application in real aquatic product sample analysis.