Niobium carbide (Nb2CTx), a key component of the MXene family renowned for its utilization in lithium-ion batteries and supercapacitors, remains largely underutilized in biosensing applications. This study introduces a notably sensitive and label-free dual-mode electrochemiluminescence (ECL) and colorimetric immunosensor to specifically detect chromogranin A (CgA) in biological fluids. Initially, Au[sbnd]Ag bimetallic nanoparticles (BiMNPs) were synthesized using Nb2CTx as a reducing and supporting material. Furthermore, a promising approach has been put forward to increase the efficacy of the ECL of [Ru (bpy)3]2+ system by integrating the combined use of the zeolitic imidazolate framework-8 (ZIF-8) and the Nb2CTx coated bimetallic NPs. Incorporation produces a significant ~165-fold increase in electrochemical signals and a 4-fold improvement in ECL signals. In particular, BiMNPs@ZIF-8 nanohybrid exhibited significantly enhanced peroxidase-like activity compared to bare BiMNPs, demonstrating synergistic peroxidase enzyme mimicry. This improved activity makes it a potent catalyst for the H₂O₂-mediated oxidation of 3,3,5,5, tetramethylbenzidine (TMB), generating the characteristic blue color. Furthermore, the ECL method achieved a detection range of 0.001 to 1000 pg/mL with LOD of 0.11 fg/mL, while the colorimetric method achieved a LOD of 100 pg/mL and a linear range of 0.1 to 4000 ng/mL. The practical applicability of the sensor was validated by analyzing CgA levels in human serum and saliva samples.
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