Defect-Engineered MIL-88B(Fe) Nanozyme for Chromophore-Free Catecholamine Detection on Paper-Based Sensing Devices

Catecholamines constitute important biomarkers for neurological and endocrine disorders, yet their routine analysis remains largely confined to centralized laboratories. Urine offers a non-invasive sample for monitoring these compounds, motivating the development of portable biosensing platforms capable of rapid and reliable detection in point-of-care (PoC) settings. In this work, we introduce a novel, simple, enzyme-free, and chromophore-free paper-based device for the fast detection of catecholamines. The sensor relies on a defect-engineered MIL-88B(Fe) nanozyme obtained through mild hydrogen peroxide treatment, which creates catalytically active sites that significantly enhance the oxidation of catecholamines. This strategy enables their direct colorimetric detection without the need for additional chromogenic reagents, simplifying the assay and improving operational safety. Integrated into a compact vertical-flow paper platform, the device is lightweight, highly stable (up to 60 days), and easy to operate, even for non-specialists. Using only 50 µL of sample, clear and stable color signals are obtained within 30 minutes. The device offers a broad linear range (1–1000 µM), acceptable precision (5% (intra-day), 5% (inter-day), and 8% (inter-batch)), and low limits of detection (0.3 µM). As a proof of concept, urine analyses demonstrated accurate performance, with recoveries of 82 to 109%, confirming its applicability in real matrices. This work represents the first use of defect-engineered MOFs in a chromophore-free paper sensor for catecholamine detection, providing a safe, cost-effective, and easily deployable tool for point-of-care (PoC) monitoring.