Enzyme-doped ion selective membrane (ED-ISM) formed with surface force and microstrucures for high perforlance urea detection

This research presents a novel technique to form a thin enzyme-doped ion selective membrane (ED-ISM) in a microfluidic chip utilizing surface tension force for on-site bio-reaction, ion selection and electrochemical detection of urea. Diamond shape microstructures assisted with neighboring air sheath flows are used to trap trace amount of polymer liquid for ED-ISM formation. Since bio-reactive enzyme of urease is immobilized on the ISM, passing urea molecules are converted into ammonia ion then diffuse through the ISM for further electrochemical detection. The produced ED-ISM has a thinner thickness (<; 10 μm) and higher surface-area than typical ISM for such that the sensing performance can be greatly enhanced due to the faster ion diffusion through the membrane. Experimental results show that the developed microchip device with the ED-ISM has good response in the concentration range from 0.1 to 1000 ppm (R²~0.9102). The limit of detection is measured to be as low as 0.1 ppm (S/N=3). Result also indicates that the response reached 95% in 8s for detecting 1 ppm of urea using the developed microchip device, which is much faster than that obtained using typical commercial ion selective electrode. The developed microchip with ED-ISM provides a low-cost yet high performance way for on-site reaction and detection of biosamples.