6. Screen printing: In this, flexible substrates like paper, cloth, etc. can be used to

draw electrodes. Conductive ink is poured over the designed mask of the elec­

trode. The obtained design on a substrate is dried in an oven. This is the most

simplistic approach. Figure 22.6a is the schematic of this approach.

7. Embossing: Herein, a mold with cavities for microchannels is made, a thermo­

plastic polymer sheet is placed over this mold, and a specific temperature and

pressure are applied. The sheet melts and occupies the shape of a cavity. Cooling

and solidification give a sensor. Figure 22.6b is the schematic of this technique.

8. Laser-cut: In this, substrates like paper, glass, carbon, plastic, polymer sheets,

etc., are ablated by lasers like CO2, UV, pulsed, diode, etc., forming laser-induced

graphene electrodes and laser-cut microchannel patterns. Figure 22.6c shows the

image of a CO2 laser cutting the polyimide sheet.

9. Ink-jet printing: In this, an ink-jet printer is employed and a conductive ink is

filled in the nozzle of the printer and sensor electrodes are printed over substrates

like paper, glass, etc. Figure 22.6d shows the image of an ink-jet printer.

22.2 Printable and Flexible Biosensors’ Applications

22.2.1 Application in Health Management

Several printable and flexible biosensors have been fabricated for monitoring health and

diagnosis of ailments. These include the detection of specific disease biomarkers or pa­

thogenic antigens in physiological samples. A few of the recent advances are discussed

here. For instance, a screen-printed biosensor was developed by Cao et al. Herein, a

paper-based 3D device was reported using a combination of screen printing and

FIGURE 22.5

Schematic representation of (a) injection molding, (b) replica molding, (c) photolithography, and (d) soft li­

thography.

Printable and Flexible Biosensors

363