A highly sensitive chemiluminescence sensor for detecting mercury (II) ions: A combination of Exonuclease III-aided signal amplification and graphene oxide-assisted background reduction

In this paper, we report a highly sensitive chemiluminescence (CL) sensor for Hg²⁺ ions based on thymine-Hg²⁺-thymine (T-Hg²⁺-T) coordination chemistry. We designed a thymine rich oligonucleotide as a capture probe and a signal probe that includes two functional domains: a horseradish peroxidase-mimicking DNAzyme domain for the generation of CL, and a recognition domain. Graphene oxide (GO) was introduced to adsorb the signal probe via p-p interaction, which brought the DNAzyme domain and GO into close proximity and quenches CL. In the presence of Hg²⁺ ions, the coordination of Hg²⁺ with the capture probe yielded a hairpin complex, triggers cascaded strand displacement reactions and Exonuclease III-assisted signal amplifications. As a result, accumulated amounts of DNAzyme were generated and released from GO, leading to an enhanced CL signal. This strategy combines enzyme-based signal amplification and GO as a background reducer, leads to a limit of detection (LOD) of 2 nmol/L. This simple detection system provides a label-free yet sensitive approach for detection of Hg²⁺ ions.