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Properties of metal–organic frameworks (MOFs) are determined by metal centers, organic ligands, and applied synthesis methods. For electrosynthesis of MOFs, the applied potential is expected to play a key role in determining the morphology, thickness, electrochemical properties, and applications of MOFs. Herein, Cu-BTC (H3BTC: 1,3,5-benzenetricarboxylic acid) films are electrosynthesized at different cathodic potentials. They feature different morphologies, thicknesses, and amounts of active copper centers, although they do show similar bonding properties, chemical compositions, phase purity, crystallinity, and surface electronic states of copper centers. Using nicotine amide adenine dinucleotide, the sensing application of these Cu-BTC films is explored, showing potential-dependent catalytic ability. Further monitoring of six other organic compounds (herein xanthine, hypoxanthine, diethylstilbestrol, estradiol, sunset yellow, and tartrazine) reveals the morphology and thickness of Cu-BTC films and the amount of copper centers inside these Cu-BTC films determines the accumulation or sensing ability of Cu-BTC films. Highly sensitive detection of these molecules individually and simultaneously is achieved with Cu-BTC electrosynthesized at −1.30 V. Electrosynthesized Cu-BTC films are thus excellent electrode materials for sensitive sensing of various analytes.

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The magnetic-bead-based electrochemical enzyme-linked immunoassay (MB-eElisa) represents an attractive approach to develop cost-effective systems that are suitable for sensing complex biological samples. Its sensitivity essentially depends on the transduction efficiency of enzyme catalytic reactions into electrochemical responses. Here, an ultrahigh signal-to-noise alkaline phosphatase (ALP)-based MB-eElisa system is developed with a renewable zinc oxide-reduced graphene oxide composite modified carbon paste electrode (ZnO@rGO/CPE). This biosensing system employs one antibody decorated MB (MB-Ab1) to capture a model tumor markercarcinoembryonic antigen (CEA)from samples, while other antibody coated gold nanoparticles-ALP bioconjugates (Ab2-AuNPs-ALP) convert 1-naphthyl phosphate (1-NPP) into electroactive 1-naphthol (1-NP). Benefitting from the unique electrochemical properties of a ZnO@rGO/CPE, including nearly zero background and significantly enhanced responses toward the hydrolyzed 1-NP in the presence of trace surfactants, the MB-eElisa system detects selectively CEA in a calibration range of 0.01–6.0 ng mL–1 and with a detection limit of 4.0 pg mL–1 (S/N = 3). Such a system was further applied to the detection of CEA in serum samples of cancer patients. The combination of MB-based ALP-linked immunoassay with a ZnO@rGO/CPE thus establishes a reusable and inexpensive electrochemical sensing platform for the rapid and sensitive detection of ultratrace biomarkers in complex biological samples.