Figure 3.

Fluid control and fluid handling: (a) schematic illustration of processes to fabricate paper-based microfluidics in an NC membrane by wax printing. It includes mainly two steps: step 1 is to print the wax pattern onto the surface of the NC membrane with a wax printer; step 2 is to bake the wax-printed NC membrane in an oven at 125 °C for 5 min to let the wax melt and penetrate through the membrane fully. Reprinted with permission from [55]. Copyright (2010) American Chemical Society. (b) Design of ”pen-writing” technique. (A) When writing biosensors on paper, the sensing elements are directly written to form patterned paper biosensors and would be expected to function at the initial location after introduction of samples leading to the fact that the colored product may not stick in the area where these biomolecules are written. (B) The proposed approach is not dependent on hydrophobic barriers to define the patterning of paper substrates, providing an alternative for sensor fabrication. Paper substrates are directly employed for the collection and transportation of samples, and then the reagent ink pen is used for sample analysis Reprinted with permission from [56]. Copyright 2019 Elsevier.