Highly Electroactive ZIF-67-Derived NiCo-LDH Nanocages as an Efficient Coreaction Accelerator for Amplifying the Electrochemiluminescence of Graphdiyne-Based Quantum Dot-Functionalized ZIF-8 in the Biomarker Immunoassay

The exploitation of innovative electrochemiluminescence (ECL) luminophores with anticipated performance and the design of an effective sensing strategy have become breakthrough research in the fields of ECL immunoassays. Herein, graphdiyne-based quantum dot (GDYQD)-modified zeolitic imidazolate framework-8 (GDYQDs/ZIF-8) was utilized as an ECL luminophore, whereas zeolitic imidazolate framework-67 (ZIF-67)-derived NiCo-layered double hydroxide (NiCo-LDH) modified by AuPd nanoparticles (NPs) (NiCo-LDH@AuPd) was employed as a coreaction accelerator for the construction of an immunosensing strategy. The GDYQDs, as a derivative of graphdiyne, possessed excellent biological properties owing to their active units and abundant surface defects, attracting considerable attention in the ECL field. In addition, ZIF-8 could not only load large amounts of GDYQDs but also effectively prevent their accumulation, maintaining stable ECL emission. Meanwhile, the ZIF-67-derived NiCo-LDH combined the merits of ZIF-67 and LDH, which not only fabricated a unique three-dimensional nanocage structure but also displayed impressive hierarchical nanoarrays resembling mussels formed by interconnected ultrathin nanosheets, thereby enhancing the charge transfer efficiency. Additionally, the synergistic interaction between NiCo-LDH and AuPd NPs in NiCo-LDH@AuPd could further enhance the ECL signal of GDYQDs/ZIF-8 by expediting the reduction of the coreactant K₂S₂O₈ to generate a greater amount of the SO₄^•- radicals. Moreover, HWRGWVC (HWR), a heptapeptide, was introduced to specifically anchor antibodies toward the Fc region, promoting the binding efficiency and sensitivity. Consequently, an ECL immunosensor with the "signal-on" type was developed for the ultrasensitive detection of neuron-specific enolase (NSE). This immunosensor displayed a wide linear range from 5 to 20 ng/mL with a detection limit as low as 1.67 fg/mL.