A widely used technique for fabrication of porous-based microfluidic devices is to create barriers within the substrates by using various kinds of hydrophobic materials. While these methods have been successfully demonstrated in various applications, solutions can penetrate into the hydrophobic barrier in an application that requires organic solvents, surfactants, or repetitive solution transfer. To avoid penetration of the solution, we have introduced new approaches for the fabrication of porous-based microfluidic devices using laser patterning. Our approaches are versatile; depending on material combination, open or enclosed microfluidic devices with 2D, passive 3D, or pressure-driven 3D fluid flow can be created. Glass microfiber, cellulose, and nitrocellulose media were used as substrates and waxy or plastic films were used as supporting materials. The multilamellar structure in our microfluidic devices comprises alternating layers of substrate and supporting media. The number of layers in the devices can be varied, therefore several microfluidic architectures can be fabricated. The fabrication procedures include two main steps. First, bonding of the substrate to the supporting material was achieved using thermal bonding or an adhesive. Second, the substrate on the supporting layer, or inside the supporting layers, was selectively ablated using a laser cutter to create barriers for microfluidic channels. Two laser systems, 10.6 µm CO2 and 455 nm diode lasers, were employed for this purpose. Utilizing the fact that the substrate layer is susceptible to ablation from the lasers, whereas the supporting layer is resistant to laser ablation (owing to its transmission at the laser wavelengths), selective ablation of only the substrate layer was achieved. The devices thus produced were successfully utilized to conduct a fluorescent immunoassay and colorimetric assays of albumin and glucose in human serum. Next steps will include application of the devices for other clinical assays such as creatinine and cholesterol.

Laser patterned multilamellar porous-media microfluidic devices for bioassays

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ACS Fall 2022

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