Green-fabricated enzyme-functionalized chitosan/Cu-BTC nanofibers for ultralow-level, room-temperature CO detection...

In this work, an innovative enzyme-functionalized chitosan/Cu-BTC nanofiber sensor was introduced for highly selective and sensitive carbon monoxide (CO) detection at room temperature. The sensor was created through green synthesis approach, where Cu-BTC (HKUST-1) was synthesized in an aqueous/ethanol medium and then blended with chitosan to form a stable, electrospinnable solution. Patterned nanofiber mats were produced through electrospinning and transferred onto interdigitated electrodes (IDEs) using a gentle press-transfer method, helping to maintain robust fiber-electrode contact and preservation of enzyme activity. Carbon monoxide dehydrogenase (CODH) was immobilized post-electrospinning, imparting exceptional selectivity toward CO over interfering gases such as NO₂, H₂, and ethanol, as demonstrated by selectivity measurements at 25 ppm (CO response: 42 % vs. <15 % for interferents). The uniform dispersion of Cu-BTC particles within the chitosan nanofiber matrix was critical in preserving the microporous framework structure while enabling flexibility and processability. The hybrid architecture ensured efficient gas diffusion, enzyme immobilization, and strong interfacial contact with the IDE substrate, forming a stable and responsive sensing interface. FTIR analysis confirmed successful coordination between Cu-BTC and chitosan, while XRD verified retention of MOF crystallinity within the polymer matrix. SEM revealed uniform fiber morphology with embedded MOF particles, and TGA confirmed a Cu-BTC loading of ∼32 % by residual weight at 600 °C. BET analysis showed a specific surface area of 422 m²/g for the Cu-BTC and 198 m²/g for the nanofiber composite. The sensor showed a rapid response time of approximately 10 s and a recovery time of 20 s across the tested CO concentrations of 1, 5, 10, 25, 50, and 100 ppm. The sensor exhibited a sensitivity of 1.76 %/ppm, a limit of detection (LOD) of ∼0.85 ppm, and a rapid response/recovery time (∼10/20 s) over a 1-100 ppm CO range within 3σ noise threshold method. Selectivity measurements at 25 ppm showed a 42 % response to CO versus <15 % for NO₂, H₂, and ethanol. The device retained >90 % of its baseline response over 30 days. These findings demonstrate that the synergistic integration of Cu-BTC, chitosan, and CODH in a nanofiber platform enables a scalable, low-power, and highly selective sensor for environmental CO monitoring.