A colorimetric and electrochemical dual-mode Hg²⁺ sensor utilizing oxidase-like activity arising from the combination of Hg²⁺ and palladium metal-organic framework@graphene

Developing convenient and reliable methods for Hg²⁺ monitoring is highly important. Some precious metal nanomaterials with intriguing peroxidase-like activity have been used for highly sensitive Hg²⁺ detection. However, H₂O₂ must be added during these detections, which impedes practical applications of Hg²⁺ sensors due to its susceptible decomposition by environmental factors. Herein, we discovered that the combination of Hg²⁺ and palladium metal-organic framework@graphene (Pd-MOF@GNs) exhibits oxidase-like activity (OXD). In the absence of H₂O₂, this activity not only catalyzes the oxidation of chromogenic substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) or o-phenylenediamine (OPD) to produce a color change but also enhances the electrical signals during OPD oxidation. Based on these properties, an effective and convenient dual-mode colorimetric and electrochemical sensor for Hg²⁺ has been developed. The colorimetric and amperometric linear relationships for Hg²⁺ were 0.045 μM—0.25 mM and 0.020 μM—2.0 mM, respectively. The proposed strategy shows good recovery in real sample tests, indicating promising prospects for multiple environmental sample detection of Hg²⁺ without relying on H₂O₂. The colorimetric and electrochemical dual-mode Hg²⁺ sensor is expected to hold great potentials in applications such as environmental monitoring, rapid field detection, and integration into smartphone detection of Hg²⁺.