Stencil printing of microfluidic paper-based analytical deevices to teach redox reactions for high school students

Abstract

Microfluidic paper-based analytical devices (μPADs) associated with colorimetric detection are attractive for applications in analytical chemistry due to their portability and instrumental simplicity. This kind of device has become popular to teach chemistry for high school students. This study describes the construction of μPADs using stencil printing technique dedicated to teaching redox reactions in high school classes. The layout with a circular sampling zone (5mm diameter) and 2 colorimetric detection zones (5-mm diameter) connected by 2 microfluidic channels (Y format) (2mm long) were drawn in Corel Draw graphics software. Then, a chromatographic paper substrate was laminated using polyester with the aid of a press at 140°C for 20s. Then, a layer of vinyl adhesive was added to the paper substrate using a spatula. The paper was cut by a paper cutter. Then, the adhesive edges of the device were removed, keeping the microfluidic geometry covered with the adhesive patterns. Finally, glass varnish was applied to create hydrophobic barriers and dried at 25°C for 30 min. The channel width was tested and optimal width was 2.5 mm wide. As a proof-of-concept, a redox reaction with sodium hypochlorite (SH) and N-N – diethyl p phenylenediamine (DPD) was chosen. The optimal volume of DPD chromogen was 1.6 µL. The complete filling of the device was achieved adding 18 µL of SH solution. The SH solution (colorless) reacts with the DPD solution (15 mmolL-1) (red) and generates a purple product. Then, 18 µL of a 1.1% v/v commercial SH solution was added into the sampling zone. After spontaneous transport through microfluidic channels, the analyte reacted with DPD reagent, generating a purple-colored product detected by naked eye. With successful preliminary results, the device will be explored to teach redox reactions and microfluidics and enables the demonstration of qualitative analysis, allowing the student to understand if the target analyte is present in the sample or not.