Preparation of novel water-stable CuMOF-74 nanoribbons and application as electrochemical labels for the detection of a chronic wound infection biomarker

Metal–organic frameworks (MOFs) have emerged as a class of highly promising porous materials, owing to their outstanding porosity and remarkable chemical tenability. However, MOFs are usually humid or water unstable, which limits severely their practical applications. In this work we present a rapid, unexpected and unprecedented transformation of CuMOF-74 nanospheres (MOF-nS) into water-stable CuMOF-74 nanoribbons (MOF-nR) upon exposure to liquid water. During this process, DMF ligands are replaced by water molecules, while the original MOF-74 crystal structure is preserved. The resultant MOF-nR are thoroughly characterized by Transmission Electron Microscopy (TEM), X-ray powder diffraction (PXRD), Fourier-transform infrared (FTIR) and Zeta potential techniques. Importantly, MOF-nR show electroactive properties coming from the framework copper, while the carboxylic functional groups present in their surface allow the easy bioconjugation with antibodies. Taking advantage of these properties, the MOF-nR are used as excellent electrochemical tags in an immunoassay for the detection of hyaluronidase, a virulence factor of gram-positive bacteria, in an artificial wound exudate fluid. MOF-nR also exhibited luminescent properties, but electrochemical detection was found to be more suitable for the tested analyte at low concentrations, reaching a detection limit of 308 ng/mL. Selectivity tests demonstrated minimal interference from other common wound biomarkers, confirming the high specificity of the developed system. The main advantages of the use of MOF-nR compared with previously reported labels are related to the cost-efficient synthesis of copper-based nanoparticle tags, coupled with a rapid and operationally simple electrochemical detection protocol, achieving detection limits comparable to the most sensitive approaches reported in the literature . • Rapid, unexpected and unprecedented transformation of CuMOF-74 nanospheres (MOF-nS) into water-stable CuMOF-74 nanoribbons (MOF-nR). • MOF-nR used as excellent electrochemical tags in immunoassay for detection of a bacterial virulence factor in an artificial wound exudate. • Lowest limits of detection reported in biosensor-related literature, together with good selectivity. • Benefits: simple and cost-effective synthesis of the nMOF-nR tags, and quicker and easier detection process due to copper electroactivity. • Possibilities for future applications of MOF-nR as tags in any immunoassay, also in combined electrochemical/optical detection.