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

Abstract

Microfluidic paper-based analytical devices (μPADs) 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 μm). 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 μm and achieves the narrowest channel barrier down to 33 ± 2 μm. As a proof-of-concept demonstration, a flexible paper-based glucose monitor is built for human health care, requiring only 0.3 μL of sample for testing.

Paper-based microfluidics in sweat detection: from design to application

“…Paper-based microfluidics can be precisely adjusted to meet various needs by varying various paper characteristics such as thickness, porosity, roughness, and wettability. [38][39][40] Patterned paper is ideal for low-cost, portable, and technically simple multiplexed bioassays. [41][42][43][44] Paper-based microfluidics offer many unique advantages over conventional microfluidics in terms of unpowered fluid transport via capillary action, high surface area to volume ratio for chemical reactions and assays, and the ability to store reagents in an active form within the fiber network.…”

Integrated membranes within centrifugal microfluidic devices: a review

“…168 Should only the microdevice itself need to remain transparent, Ma, et al recently demonstrated stable and controllable patterning of cellulose microfibers onto either polymeric or silicate substrates. 169 For applications where the cellulose membrane itself would optimally exhibit some degree of transparency, isorefractive matching has also been demonstrated as a unique means of improving detectability of functionalized gold nanoparticles. 36 Alternatively, cellulose nanofiber (CNF) papers offer superior optical, thermal, and mechanical strength characteristics relative to standard microfiber cellulose.…”