An electrochemical sensor for bacterial lipopolysaccharide detection based on dual functional Cu²⁺-modified metal–organic framework nanoparticles

An electrochemical sensor based on dual functional Cu²⁺-modified metal–organic framework nanoparticles (Cu²⁺-NMOFs) for sensitive detection of bacterial lipopolysaccharide (LPS) is reported. Cu²⁺-NMOFs were prepared and characterized by SEM, EDS, XRD, and XPS. In this LPS sensor, LPS firstly immobilized in gold nanoparticles/reduced graphene oxide by C18 alkane thiol chains, since the LPS can interact with the C18 alkyl chains by strong intermolecular interactions. Then the Cu²⁺-NMOFs were captured by the anionic groups of the carbohydrate portions of LPS molecules and played a vital role of recognition unit. More importantly, the Cu²⁺-NMOFs can catalyze dopamine oxidation to generate aminochrome, resulting in a strong electrochemical oxidation signal. The electrochemical sensor based on dual functional Cu²⁺-NMOFs was investigated by differential pulse voltammetry, and the stripping peak currents of dopamine oxidized to aminochrome were used to monitor the level of LPS. The developed method demonstrated a wide linear range from 0.0015 to 750 ng/mL with a limit of detection of 6.1 × 10⁻⁴ ng/mL. The fabricated sensor was applied to detect LPS in mouse blood serum and satisfactory results were achieved. Compared to other detection schemes by using the LPS-binding proteins, peptides, and aptamer, the proposed LPS determination based on the catalytic peroxidase-mimicking NMOFs has some advantages such as good reproducibility, low detection limit, and excellent specificity.