Modifying Wicking Speeds in Paper-Based Microfluidic Devices by Laser-Etching

Abstract

Paper-based microfluidic devices are an attractive platform for developing low-cost, point-of-care diagnostic tools. As paper-based devices’ detection chemistries become more complex, more complicated devices are required, often entailing the sequential delivery of different liquids or reagents to reaction zones. Most research into flow control has been focused on introducing delays. However, delaying the flow can be problematic due to increased evaporation leading to sample loss. We report the use of a CO2 laser to uniformly etch the surface of the paper to modify wicking speeds in paper-based microfluidic devices. This technique can produce both wicking speed increases of up to 1.1× faster and decreases of up to 0.9× slower. Wicking speeds can be further enhanced by etching both sides of the paper, resulting in wicking 1.3× faster than unetched channels. Channels with lengthwise laser-etched grooves were also compared to uniformly etched channels, with the most heavily grooved channels wicking 1.9× faster than the fastest double-sided etched channels. Furthermore, sealing both sides of the channel in packing tape results in the most heavily etched channels, single-sided, double-sided, and grooved, wicking over 13× faster than unetched channels. By selectively etching individual channels, different combinations of sequential fluid delivery can be obtained without altering any channel geometry. Laser etching is a simple process that can be integrated into the patterning of the device and requires no additional materials or chemicals, enabling greater flow control for paper-based microfluidic devices.

Microfluidic Paper-Based Analytical Devices: From Design to Applications

“…For example, laser etching of a commercial hydrophobic coated paper (e.g., parchment paper, wax paper, palette paper), as reported by Chitnis et al, enables selective modification of the paper to allow for localization of aqueous reagents . Laser etching can also be applied to a native, hydrophilic paper to tune the wicking speed of the PAD . Laser cutting enables the fabrication of a stand-alone PAD.…”

“…37 Laser etching can also be applied to a native, hydrophilic paper to tune the wicking speed of the PAD. 38 Laser cutting enables the fabrication of a stand-alone PAD. With no hydrophobic barrier used, the PAD can be employed for applications that involve organic solvents.…”

Mechanistic Understanding and Three‐Dimensional Tuning of Fluid Imbibition in Silica‐Coated Cotton Linter Paper Sheets

“…[ 1,2,5,21,27,35,32,36 ] Shaping techniques are relatively expensive due to the necessary equipment. [ 10,23,35,37–39 ] Tuning fluid transport through the fiber type, fiber density, or paper grammage bares the advantage of simple integration into existing paper fabrication processes. None of these approaches allows to tune fluid flow in all three dimensions of a paper sheet, although, this would open new possibilities such as sensitivity enhancement and the design of multifunctional microfluidic paper‐based devices or asymmetric wettability for paper‐based separation and packaging.…”

A Low-Cost 3-in-1 3D Printer as a Tool for the Fabrication of Flow-Through Channels of Microfluidic Systems

“…CO 2 laser-based fabrication of microfluidic substrates has, for example, been performed with common materials such as glass and poly methylmethacrylate (PMMA) sheets and the influence of the laser settings and the length and strength of surface treatments on the production of optimal microchannel profiles and on surface smoothness was demonstrated [ 32 , 33 ]. Applications of laser-fabricated microfluidic devices include droplet digital polymerase chain reaction (PCR) [ 34 ], droplet generation [ 35 ], wicking speed modulation on paper microfluidic devices [ 36 ] and culturing of embryonic bodies [ 37 ]. Feasibility trials have also been conducted with standalone devices for CNC milling [ 5 ] and 3D FDM printing [ 38 , 39 , 40 , 41 ], with satisfactory results.…”