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.
Highlights
Paper-based microfluidic devices are an attractive platform for developing low-cost, point-of-care diagnostic tools [1,2,3]
The simplest paper-based devices are lateral flow devices, where liquid wicks in one direction along the paper strip. These are suitable for simple detection chemistries; for more complex reactions, devices that are more complicated are required, and this frequently entails the sequential delivery of different liquids or reagents to reaction zones
Solutions of bovine serum albumin conjugated with Texas Red (BSA-TR) were wicked along channels etched at various levels (0%, 50%, and 100%) to determine if the laser-etched paper inhibits protein transport
Summary
Paper-based microfluidic devices are an attractive platform for developing low-cost, point-of-care diagnostic tools [1,2,3]. To increase wicking speeds beyond the limits of a given substrate, most attempts have focused on having the fluid travel outside the paper in external capillaries, either by sandwiching the paper between polymer films [24,25], creating multi-ply structures [26,27,28], or by removing portions of the paper to create empty channels for the liquid to flow through [29,30,31,32,33] These techniques can result in much faster wicking, as much of the liquid is able to bypass the paper matrix entirely. By selecting the appropriate etching level, the desired wicking behavior can be achieved
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