Ultra-sensitive Fiber-OECT biosensor enabled by ZIF-67/f-MWCNT for noninvasive urea monitoring

Urea is a key biomarker for diagnosing various kidney and liver disorders, which can be assessed through sensing platforms. However, existing urea sensors have performance issues in real samples. Herein, a novel fiber-organic electrochemical transistor (F-OECT) sensing platform was constructed by sequentially depositing cobalt-based metal-organic framework material (ZIF-67), carboxylated multi-walled carbon nanotubes, poly (3,4-ethylenedioxythiophene), and urease on cotton fibers for urea determination. The resulting F-OECT sensor exhibited excellent performance toward urea detection with a high sensitivity (82.91 μA/decade). This performance is attributed to the synergistic effect of the hierarchical composite: the significantly enlarged electrochemically active surface area of PEDOT/f-MWCNT/ZIF-67 facilitates high-density urease immobilization, while the conductive network ensures efficient signal transduction, coupled with the intrinsic signal amplification of the OECT architecture. Under optimized conditions, the F-OECT sensor illustrated a wide linear response range (1 pM-10 mM) and a low detection limit of 1 pM toward the detection of urea, coupled with an excellent selectivity, reproducibility, and stability. More importantly, the F-OECT sensor was able to detect urea in real sweat and urine samples. Based on these encouraging data, the F-OECT sensor was connected to a printed circuit board to transmit signals via Bluetooth, and the results showed a sensor capable of visually quantifying urea. Overall, the proposed F-OECT sensor looks promising for future non-invasive and sensitive liquid detection of urea, thereby deserving further research and development.