FIG. 12.

Multilayer 3D microfluidic devices. (A) Microfluidic chip design that has four paper layers and three tape layers. The hydrophobic walls (black areas) of the paper layers were printed with a Xerox Phaser 8560 wax printer. The blank regions (colored areas) were created with hydrophilic paper to drive the flow of samples vertically and horizontally. The tape layers were patterned by holes which connected channels of the different paper layers. (B) Photograph of top of the 3D paper-based chip which has four sample inlets (a–d), which perform four assays. (C) Photograph of the bottom of the chip dipped in metal-contaminated water. There was a color change in each of the detection zones [brown color, pink-red color, yellow-red color, and reg magenta color in the presence of Cu (II), Ni (II), Cd (II), and Cr (VI), respectively]. In each of the four detection regions (a–d), which correlate to four samples, 4 × 4 metal identifications occur in each region.¹³⁸ Reproduced with permission from Wang et al., Anal. Bioanal. Chem. 406, 2799–2807 (2014). Copyright 2014 Springer Nature Switzerland AG.