A fully integrated passive microfluidic Lab-on-a-Chip for real-time electrochemical detection of ammonium: Sewage...

The present work reports on the development of a new generation of Lab-on-a-chip (LOC) to perform in-situ and real-time potentiometric measurements in flowing water. The device consisted of two differentiated parts: a poly (dimethylsiloxane) (PDMS) microfluidic structure obtained by soft lithography and a fully integrated chemical sensing platform including four working microelectrodes, two reference microelectrodes and one counter microelectrode for detecting ammonium in a continuous mode. The performance of the device was evaluated following its potentiometric response when analyzing ammonium containing samples. As a key parameter, its time of response was compared to that of a commercially available electrical conductivity sensor used as reference sensor during tests in laboratory using flowing tap water and technical scale using flowing wastewater. As a result, the LOC showed a slope of 55 mV/decade, a limit of detection of 4·10^-5 M and a time of full response between 10 and 12 s. It was demonstrated that the device can provide fast and reliable data at real time when immersed in a laminar flow of water. Moreover, the test of robustness showed that it was still functional after immersion in sewage for at least 15 min. Besides, the LOC reported here can be helpful for a wide variety of flowing-water applications such as aqua culture outlets control, in-situ and continuous analysis of rivers effluents and sea waters monitoring among others.