Metal-organic framework/graphene oxide Van der Waals heterostructure for label-free electrochemical nanoimmunosensing of procalcitonin.

Metal-organic frameworks (MOFs) are at the forefront of materials research due to their high area-to-volume ratio, tunable porosity, host-guest adsorption capabilities, and improved optical, fluorescent, conductive, and electromagnetic properties. Van der Waals heterostructures (VWHs) are 2D materials, including MOFs and graphene oxide (GO), among others, stacked like building blocks defined with one-atomic-plane precision by weak, reversible interactions that synergistically integrate their features to create new structures with enhanced properties. For example, MOF-based architectures enable the adsorption of numerous small molecules, such as electroactive probes and biomolecules, which can be linked to GO to form VWHs and stably coupled to an electrode surface, thereby enhancing the electrode's response and making them promising for the development of highly sensitive biosensors. In this work, VWHs were assembled by stacking Ni3(HITP2) MOF and GO, which were deposited on screen-printed carbon electrodes (SPCE) by drop-casting and characterized by electrochemistry, spectroscopy, and microscopy. They showed better conductive properties than bare and modified electrodes with the corresponding materials separately, thus offering a highly conductive surface area that permits the adsorption of toluidine blue O (TB), an in-situ electrochemical probe, and multiple anchoring points of procalcitonin capture antibodies. As a result, a label- and reagent-free nanoimmunosensor platform was developed for the detection of procalcitonin in one step, showing high sensitivity (0.099 μA*mL/pg) and high specificity over a linear range from 4.25 to 125.00 pg/mL, with a limit of detection (LOD) of 4.25 pg/mL by square wave voltammetry (SWV). The nanoimmunosensor performance was tested in spiked human serum, with recovery greater than 90%, and in real samples, demonstrating high discrimination between positive and negative samples and strong correlation with a gold standard method. Procalcitonin levels, in the context of a panel of infection biomarkers, provide information not only about diagnosis but also prognosis, infection severity, and sepsis risk.