LAUSR

We present a paper microfluidic device capable of conducting enzyme-linked assays: a microfluidic enzyme-linked paper analytical device (μEL-PAD). The system exploits a wash-free sandwich coupling to form beads/analyte/enzyme complexes, which are subsequently added to the vertical flow device composed of wax-printed paper, waxed nitrocellulose membrane and absorbent/barrier layers. The nitrocellulose retains the bead complexes without disrupting the flow, enabling for an efficient washing step. The entrapped complexes then interact with the chromogenic substrate stored on the detection paper, generating a color change on it, quantified with an open-source smartphone software. This is a universal paper-based technology suitable for high-sensitivity quantification of many analytes, such as proteins or nucleic acids, with different enzyme-linked formats. Here we demonstrate the potential of the μEL-PAD to detect DNA from Staphylococcus epidermidis. After generation of isothermally amplified genomic DNA from bacteria, Biotin/FITC-labeled products were analyzed with the μEL-PAD, exploiting streptavidin-coated beads and antiFITC-horseradish peroxidase. The μEL-PAD achieved a limit of detection and quantification < 10 genome copies/μL, these being at least 70- and 1000-fold lower, respectively, than a traditional lateral flow assay exploiting immobilized streptavidin and antiFITC-gold nanoparticles. We envisage that the device will be a good option for low-cost, simple, quantitative, and sensitive paper-based point-of-care testing. This article is protected by copyright. All rights reserved.