Rapid Assembly of Cellulose Microfibers into Translucent and Flexible Microfluidic Paper-Based Analytical Devices via Wettability Patterning

Microfluidic paper-based analytical devices (mu PADs) are emerging as powerful analytical platforms in clinical diagnostics, food safety, and environmental protection because of their low cost and favorable substrate properties for biosensing. However, the existing top down fabrication methods of paper-based chips suffer from low resolution (> 200 mu m). Additionally, papers have limitations in their physical properties (e.g., thickness, transmittance, and mechanical flexibility). Here, we demonstrate a bottom-up approach for the rapid fabrication of heterogeneously controlled paper-based chip arrays. We simply print a wax-patterned microchip with wettability contrasts, enabling automatic and selective assembly of cellulose microfibers to construct predefined paper-based microchip arrays with controllable thickness. This paper-based microchip printing technology is feasible for various substrate materials ranging from inorganic glass to organic polymers, providing a versatile platform for the full range of applications including transparent devices and flexible health monitoring. Our bottom-up printing technology using cellulose microfibers as the starting material provides a lateral resolution down to 42 +/- 3 mu m and achieves the narrowest channel barrier down to 33 +/- 2 mu m. As a proof-of-concept demonstration, a flexible paper-based glucose monitor is built for human health care, requiring only 0.3 mu L of sample for testing.