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Microfluidic paper-based analytical devices (µPADs) are relatively new group of analytical tools that represent an innovative low-cost platform technology for fluid handling and analysis, enabling simple fabrication/operation and equipment independence and provide a wide range of applications. Nonetheless, µPADs lack in the effective handling and controlling of fluids, which leads to a main drawback for their reproducibility in large volumes during manufacturing, their transition from laboratory into the market and thus accessibility by the end-users. Herein we investigate the applicability of ionogel materials based on a poly(N-isopropylacrylamide) gel with the 1-ethyl-3methylimidazolium ethyl sulfate ionic liquid as fluid flow manipulator in µPADs using the ionogel as a negative passive pump to control the flow direction in the device. A big challenge undertook by this contribution is the integration of the ionogel materials into the µPADs. Finally, the characterisation and the performance of the ionogel as a negative passive pump were demonstrated.

A combination of atomic layer deposition and photolithography is applied to fabricate interdigitated electrodes of aluminum-doped zinc oxide embedded in polyethylene terephthalate substrates. Various designs with different gap to widths ratios are realized and important characteristics of the electrodes, including thickness, surface roughness, and electrical properties with different ZnO:Al 2 O 3 ratios are studied. Oxygen plasma is applied to etch the polyethylene terephthalate surface and to embed the electrodes, a methodology which is a breakthrough toward ultimately thin devices fabrication. Moreover, the influence of oxygen plasma on the electrical properties of aluminum-doped zinc oxide is analyzed in more detail. Electrochemical impedance spectroscopy studies of two different stimuli responsive ionogels are performed using the fabricated electrodes. The results show the suitability of the use of the fabricated electrodes to monitor changes in ion motion and morphology of stimuli responsive materials. These electrodes and the process of characterization of the ionogels presented could be implemented to monitor electrochemical changes in real applications such as protective coatings.

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The main problem for the expansion of the use of microfluidic paper-based analytical devices and, thus, their mass production is their inherent lack of fluid flow control due to its uncontrolled fabrication protocols. To address this issue, the first step is the generation of uniform and reliable microfluidic channels. The most common paper microfluidic fabrication method is wax printing, which consists of two parts, printing and heating, where heating is a critical step for the fabrication of reproducible device dimensions. In order to bring paper-based devices to success, it is essential to optimize the fabrication process in order to always get a reproducible device. Therefore, the optimization of the heating process and the analysis of the parameters that could affect the final dimensions of the device, such as its shape, the width of the wax barrier and the internal area of the device, were performed. Moreover, we present a method to predict reproducible devices with controlled working areas in a simple manner.