Figure 1.

Schematic illustration of the fabrication of the napkin-based capacitive sensor. (a) Fabrication process. Step 1: A folded paper with hollowed pattern coated with polydimethylsiloxane (PDMS). Step 2: A piece of napkin is inserted into the folded paper, resulting in hydrophilic and hydrophobic pattern on the napkin. Step 3: Adding silver nanowires (NWs) in ethanol solution to the patterned napkin. Step 4: Packing it with PU film. Step 5: Two pieces of the electrode plates are coupling to form a capacitive sensor. (b) Photographs of the folded paper, hydrophilic–hydrophobic patterned napkin, single-electrode plate, and capacitive sensor.