Development and application of p-NIPAM Barriers and Repositories for Microfluidic Flow Control. A Proof of Concept Torres-Molina, María Angustias Ramos Lorente, Celia Esperanza Orbe Payá, Ignacio De López Ruiz, Nuria Escobedo Araque, Pablo Palma López, Alberto José Capitán Vallvey, Luis Fermín Erenas Rodríguez, Miguel María Pérez de Vargas Sansalvador, Isabel María Flow control μPAD P-NIPAM This research was funded by Spanish MCIN/AEI/10.13039/501100011033/with project PID2022-138727OB-I00. The project was partially supported by European Regional Development Funds “ERDF A way of making Europe”. Funding for open access charge: Universidad de Granada / CBUA. Passive fluid flow is not sufficient to meet new analytical requirements, therefore further research is needed in the field of flow control in order to improve the application of microfluidic systems. In this work, stimuli-sensitive materials have been studied to act as barriers and repositories to be integrated in µPADs. Poly(N-isopropylacrylamide) (p-NIPAM) has been studied to act as a reservoir and flow retardant. As a reservoir, the swelling/de-swelling behaviour has been characterised as a function of temperature, kinetics, reservoir size and the influence of pH. As a flow retardant, a p-NIPAM ionogel was used to significantly slow down the flow and even stop it. This is very useful for preventing the mixing of reagents until a certain point in time or for controlling where the mixing occurs. The ionogel volume and the delay time were optimised. As proof of concept, they were used in a colorimetric µPAD for nitrite determination based on the Griess chemistry. The results demonstrate the feasibility of integrating the developed stimulus-sensitive materials in µPADs, enabling new applications where these tools are required. 2026-03-11T10:25:04Z 2026-03-11T10:25:04Z 2026-03-06 journal article M.A. Torres-Molina et al. Microchemical Journal 224 (2026) 117598. https://doi.org/10.1016/j.microc.2026.117598 https://hdl.handle.net/10481/112031 10.1016/j.microc.2026.117598 eng http://creativecommons.org/licenses/by-nc-nd/3.0/ open access Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License Elsevier