Ultrasensitive Electrochemiluminescence Detection of Dual Tumor Markers on Living Cell Surface with a Closed Bipolar Electrode Array Chip

High-sensitivity in situ analysis for detecting dual tumor markers on the cell surface is crucial for the precise early diagnosis and identification of the disease status. Herein, a closed bipolar electrode array-based electrochemiluminescence (c-BPE-ECL) chip was developed for the simultaneous detection of carcinoembryonic antigen (CEA) and α-fetoprotein (AFP) on the tumor cell surface. Based on the exceptional properties of covalent organic framework (COF) materials, including a large specific surface area, porous crystalline structure, and abundant amino active sites, along with the excellent conductivity and remarkable biocompatibility of gold nanoparticles (Au NPs), a bifunctional signal probe, COF@Au@MB-Apt, was successfully synthesized. This probe was capable of loading a significant amount of the signal molecule methylene blue (MB) and the targeting recognition unit aptamer (Apt), aiming to enhance the sensitivity and selectivity. Using MCF-7 cells as a model, under an appropriate potential, the MB molecules targeted on the cell surface of the BPE cathode were reduced. This process, driven by the principle of electrical neutrality, triggers the anodic Faradaic reaction, resulting in the ECL signal of the [Ru(bpy)₃]²⁺/tripropylamine (TPA) system. The developed c-BPE-ECL system exhibited high sensitivity for the detection of CEA and AFP, with calculated detection limits of 6.12 pg mL^-1 and 0.25 pg mL^-1, respectively. Additionally, the quantities of CEA and AFP expressed on individual MCF-7 cells were determined to be 37 and 0.25 fg per cell. Meanwhile, the constructed c-BPE-ECL platform demonstrated high sensitivity and excellent stability, selectivity, and reproducibility. These attributes collectively make it a versatile and highly promising platform for detecting various cancer cells and cancer-relevant biomarkers.