Laser melting of Parafilm-wax: a novel approach to hydrophobic barrier formation in paper-based microfluidics

We present a novel method for fabricating microfluidic paper-based analytical devices (μPADs) using laser melting of Parafilm wax to form hydrophobic barriers. This approach involves placing Parafilm on filter paper and patterning it with a CO₂ laser, which locally melts the wax to create embedded flow barriers. Crucially, the Parafilm is peeled off post-patterning, preserving both surfaces of the paper and enabling vertical flow assays. Optimal laser parameters were determined to ensure consistent barrier formation without damaging the paper. The technique enabled the fabrication of channels as narrow as 800 μm. Compatibility with biochemical assays was confirmed through colorimetric detection of glucose and protein, and through a vertical flow enzyme-linked immunosorbent assay (ELISA) for human IgG, with a detection limit of 3.9 ng mL^-1. This single-step, reflow-free method is simple, reproducible, and accessible, leveraging materials and equipment readily available in standard laboratories. It lowers the technical barriers to μPAD fabrication and enables both planar and vertical assay formats, expanding the scope of paper-based diagnostics for point-of-care applications.