Highly Electroactive Ti3C2T x MXenes@TiO2–PdNCs as an Efficient Coreaction Accelerator for Amplifying the Aggregation-Induced Electrochemiluminescence of Self-Enhanced Cu:Gd-TCPE-MOF in Biomarker Immunoassays

The development of high-performance electrochemiluminescence (ECL) luminophores, coupled with efficient sensing approaches, constitutes a critical breakthrough in ECL immunoassays. Herein, Cu2+-incorporated Gd-based metal–organic framework (Cu:Gd-TCPE-MOF) was utilized as a self-enhanced aggregation-induced electrochemiluminescence (AIECL) luminophore, while electroactive Ti3C2Tx MXenes@TiO2 nanosheets modified with Pd nanocubes (NCs) (Ti3C2Tx Mxenes@TiO2–PdNCs) served as the coreactant accelerator to construct an immunoassay platform. Cu:Gd-TCPE-MOF, synthesized through coordination assembly with 1,1,2,2-tetra(4-carboxylphenyl)ethylene (H4TCPE) as the AIECL ligand, Gd3+ as the metal center, and Cu2+ as the dopant, has triggered both the AIE effect and self-enhanced ECL performance originating from the catalysis of incorporated Cu2+. Simultaneously, the Ti3C2Tx MXenes@TiO2 heterojunction was obtained via in situ TiO2 growth using conductive Ti3C2Tx MXenes as the titanium source, which not only constructed uniformly dispersed interconnected nanosheets to improve coreactant accessibility, but also facilitated electroactive intermediate diffusion. Additionally, the synergistic effect between Ti3C2Tx MXenes@TiO2 and PdNCs within Ti3C2Tx MXenes@TiO2–PdNCs could further accelerate the electron transfer and promote the generation of more radicals, boosting the ECL signal of Cu:Gd-TCPE-MOF. Furthermore, a site-specific antibody immobilization approach based on the HWRGWVC (HWR) heptapeptide was proposed, and this strategy effectively preserved antibody bioactivity and improved the incubation performance of immunoassay. Benefiting from the above-mentioned superiorities, a “signal-on” type ECL immunosensor was successfully achieved for the ultrasensitive analysis of neuron-specific enolase (NSE), revealing a broad linear range from 5 fg/mL to 50 ng/mL with a low limit of detection of 1.67 fg/mL (S/N = 3).