Chromium-functionalized metal-organic frameworks as highly sensitive, dual-mode sensors for real time and rapid...

Dopamine (DA): the brain's "feel-good" chemical that keeps us motivated, happy, and ready to take on the world. This essential neurotransmitter is involved in various physiological processes such as motor control, reward, and mood regulation. Dysregulation of DA levels is linked to several neurodegenerative diseases, emphasizing the need for sensitive and accurate detection methods for both diagnostic and therapeutic purposes. Fluorometric sensing presents an appealing, cost-effective approach to detect DA, especially in complex biological fluids. In this study, we report the synthesis and application of chromium-based metal-organic frameworks (MOFs), Cr-IA and Cr-BTC (IA: itaconic acid and BTC: benzene-1,2,4-tricarboxylic acid), as highly sensitive fluorometric sensors for DA detection in bio-fluids. Cr-IA and Cr-BTC MOFs were synthesized using a solvothermal method with their respective ligands and chromium salts, utilizing a mixed solvent system comprising water, ethanol, and dimethylformamide (DMF). Both MOFs were characterized using a variety of techniques, including Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), zeta potential measurements, and energy-dispersive X-ray spectroscopy (EDS) that provided essential information on the structural integrity, surface morphology, crystallinity, thermal stability, and surface charge properties of the MOFs, confirming the successful synthesis and characterization of both materials. The synthesized MOFs exhibited remarkable fluorometric sensing capabilities for dopamine detection in HEPES buffer, aqueous solution, and human serum, showcasing strong fluorescence response with high sensitivity, selectivity, and stability across a wide pH range. Cr-IA MOF demonstrated a 3.4-fold fluorescence intensity increase in HEPES buffer, while Cr-BTC MOF achieved a 5-fold enhancement. Both MOFs showed low limits of detection, with Cr-IA and Cr-BTC achieving 21 nM and 41 nM in HEPES buffer, and 26 nM and 20 nM in water, respectively. Fluorescence quenching and visible color changes upon dopamine addition enabled real-time and visual detection, while their dose-response behavior in human serum further validated their reliability for bioanalytical applications. Cytotoxicity studies confirmed their biocompatibility, ensuring their safe use in biological systems. These findings establish Cr-IA and Cr-BTC as highly promising materials for diagnostic and therapeutic monitoring, offering potential for clinical diagnostics and broader biomedical applications.