Ion-selective Membrane Formed in a Microfluidic Chip Utilizing Surface Tension Force for High Sensitive Ammonia Ion Sensing

This research presents a novel method to produce successive polymeric ion-selective membrane (ISM) embedded in a microfluidic chip with electrochemical electrodes for detecting ammonia ions. The ISM was formed inside the microchannel utilizing a simple flow-through forming technique. Surface tension force on microstructures is used to trap trace amount of polymer liquid doped with ammonia ionophores and form the ion-selective membrane after curing. Series of ion selective membrane with the thickness of around 50 μm can be formed in the microfluidic chip. Due to thinner thickness and higher surface-area of the formed membranes, the sensing performance can be greatly enhanced due to the faster ion diffusion through the ISM. Results show that the developed microchip has a good linear response for detecting ammonia ion of the concentration between 0.0001 and 1000 ppm (R~0.9689) and the limit of detection is measured to be as low as 0.1 ppb. The time response for measuring 0.01 ppm of ammonia ion is only 4 s (95% standard) which is much faster than that of using typical commercial ISE products (~ minutes). The developed microchip with integrated ion-selective membrane provides a low-cost yet high performance way for continuous detecting ammonia ions.