Local Photo-Polymer Deposition-Assisted Fabrication of Multilayer Paper-Based Devices

In this paper, we report on the use of a local acrylate-based negative photo-polymer deposition technique for the fabrication of 3D microfluidic paper-based analytical devices (3D-mu PADs) where the sample flows in both the lateral and vertical directions through multiple stacked layers of porous materials. A simple and inexpensive manufacturing method was used, which is based on the local deposition of a photo-polymer (deposition speed 30 mm/s) on a porous cellulose paper substrate followed by the subsequent exposure (scanning speed 30 mm/s) to a laser source (fibre coupled continuous wave at 405 nm with maximum power of 60 mW), to stack four layers of cellulose paper and make 3D multilayer mu PADs. With this technique, we provide a pathway to eliminate the limitations that other reported methods have during the fabrication of mu PADs such as the need for multiple sophisticated alignments between adjoining layers and the use of additional tools to ensure adequate contact between the layers. In this study, we demonstrate the usefulness of our four-layer 3D-mu PAD for simultaneous detection of three analytes, namely BSA, glucose, nitrite spiked in artificial urine and also the pH of the tested sample, through single step colorimetric assays with the limit of detection found at 0.4 mg/mL for BSA, 14.5 mu g/mL for glucose and 2.5 mu g/mL for nitrite. Our 3D-mu PAD fabrication methodology can also be adapted in more complex analytical assays where multiple steps are needed for applications in point-of-care diagnostics.