Fig. 5.

(a) A schematic showing the design and working principles of 3D slip-PADs. A movable slipping design is used in conjunction with multiple layers stacked on top of one another. The device enables a one-step process for sequential fluid movement to the detection site. The black and white areas illustrate the hydrophobic wax boundary and hydrophilic fluid route, respectively. (b) Structural components of 3D slip-PADs. (1: 3D layers, 2: conjugate pad, 3: nitrocellulose membrane, 4: wicking pad, and 5: adhesive pad). (c) (i) representative scheme of gold enhancement for signal amplification on the 3D slip-PADs. The size-enlarged AuNPs resulted in signal intensification, and (ii) photographs of the PAD obtained before and after gold enhancement at a target IgG (500 ng/mL). Reproduced from Refs. [81] with permission of Nature Research.