Features in Microfluidic Paper-Based Devices Made by Laser Cutting: How Small Can They Be?

Area of Science:

• Materials Science
• Analytical Chemistry
• Microfluidics

Background:

• Microfluidic paper-based analytical devices (µPADs) offer low-cost, portable diagnostic solutions.
• Laser cutting is a precise method for fabricating microchannels in paper substrates.
• Understanding feature size limitations is crucial for µPAD design and performance.

Purpose of the Study:

• To determine the minimum feature size for fluid flow in laser-cut µPADs across various paper types.
• To investigate the relationship between paper fiber width and the smallest flow-enabling feature size.
• To analyze fluid flow speed in microscale channels fabricated from different paper materials.

Main Methods:

• Fabrication of microfluidic channels using laser cutting on five distinct paper types.
• Experimental determination of the smallest feature size allowing successful fluid flow for each paper type.
• Measurement of fluid flow speed (Allura red dye) through microscale channels of varying widths.

Main Results:

• Smallest feature sizes enabling fluid flow ranged from 24 ± 3 µm (nitrocellulose membrane) to 139 ± 8 µm (filter paper).
• A direct correlation was observed between paper fiber width and the smallest feature size capable of sustaining fluid flow.
• Fluid flow speed was significantly slower in microscale channels compared to millimeter-scale channels, with wider channels exhibiting faster flow.

Conclusions:

• Paper type and its inherent fiber width are critical determinants of the smallest feature size for functional µPADs.
• Laser cutting parameters must be optimized based on paper substrate properties to achieve desired microchannel dimensions.
• The principles governing fluid dynamics in microscale paper channels align with those observed in larger formats, emphasizing the importance of channel width for flow rate.