Immunodetection of D-dimer on a microfluidic paper-based analytical device

A microfluidic paper-based analytical device (µPAD) was created by wax printing on a single piece of Whatman N. 1 chromatographic paper (1.5 cm x 4.5 cm, 0.18 mm thick) and combined with an anti-D-dimer capture antibody and conjugates of anti-D-dimer antibody with 40 nm gold nanoparticles. The design comprises: i) a circular area (ID 0.5 cm) for sample addition (S), ii) a linear channel (2.6 cm long), iii) circular areas where test (T) and control (C) reactions take place (ID 0.5 cm) and iv) a rectangular reservoir (1.0 cm x 1.4 cm). The μPAD on the top was used to test a sample with 1 x 10⁵ ng/mL D-dimer (12 μL), whereas the μPAD on the bottom was run with a control (no D-dimer) sample. The video clearly shows the capture of the D-dimer:antibody-AuNP complex by the antibody immobilized in the circular test zone in the top μPAD. This capture is signaled by the formation of a red spot, which is absent in the test zone of the bottom µPAD, which was run with a control (no D-dimer) sample.