polyimide laser-induced graphene. Further, these were modified with carbon nanotubes

and enzymes. This gave a power density of 4.7 µW/cm² at 260 mV. Figure 22.6D is the

real image of their device reprinted [18]. The same author also developed a carbon cloth

electrode-based, enzymatic biofuel cell. This gave a power density of 24.8 µW/cm² at

300 mV. Figure 22.6E is the reprint of their real image [19]. Jayapiriya et al. also developed

carbon paste electrodes fabricated with a PCB printer. Further, gold nanorods were im­

mobilized on these to form enzymatic glucose biofuel cells. This gave maximum energy of

8.8 µW/cm² [36]. Hence, printable and flexible biosensors, especially enzymatic and

microbial, have proven to be quite useful in energy-harvesting biofuel cell applications.

22.2.3 Applications in Environmental Monitoring

For spontaneous environmental monitoring, to measure the environmental impact load,

real-time, portable detection systems for field applications are crucial. These could reduce

the limitations like collection and logistics of a sample, handling, and other such issues. In

this context, printable and flexible biosensors have proven to be advantages. Quite a few

research groups have worked on developing these types of sensors for monitoring var­

ious environmental parameters. McConnell et al. gave a detailed review of aptamer-based

biosensors for environmental parameters monitoring. The review covers various biosensors

reported for detection of microbial contamination, heavy metal, metal ions, toxins, in­

dustrial waste, pesticides, pharmaceutical remains in water and soil [37]. Song et al. also

reported a detailed review about array-based biosensors using DNA-, enzyme-, aptamer-,

antibody-, and micro-organism-based bioreceptors [38]. Avramescu et al. reviewed gra­

phite screen-printed biosensors for food and environment quality monitoring [39].

Honeychurch presented a view about screen-printed biosensors for metal pollutants de­

tection [40]. Laschi et al. reviewed advances in disposable biosensors for the detection of

food and environmental pollutants [41]. In an interesting work, a microfluidic biochip was

developed by Brennan et al. Herein, fish cells of rainbow trout gill epithelial cells were

used as bioreceptors. These were used for the detection of pesticide toxicity for water

quality assessment [42]. Likewise, Lin et al. developed a screen-printed biosensor with a

combination of antibody and horseradish peroxide enzyme for selective detection of E. coli.

Carbon-based electrodes modified with gold nanoparticles were used as a matrix

to immobilize these antibodies [43]. In a remarkable work, Rupesh et al. reported a lab on a

flexible glove-based, printed biosensor. This had great stretchability and could be used as a

point of care wearable sensor. A carbon ink was screen printed over the glove as an electrode.

Similarly, Ag/AgCl ink was screen printed and used as a reference electrode. Over the

working carbon ink electrode, an enzyme organophosphorus hydrolase (OPH), was coated

as a bioreceptor. This enzyme was mixed with Nafion and this solution was coated. This was

utilized for the detection of organophosphate, a common pesticide. In further, this biosensor

was integrated with electrochemical analysis and wireless transmission of data via smart­

phone. This could be used in food quality assessment [44].

Similarly, Tirgil et al. prepared an aptamer-based sensor using a single-walled carbon

nanotube matrix. This was used for the detection of an antibiotic, oxytetracycline, in

water samples. This is used as a medicine for pathogenic infection in livestock. Its por­

table size, high stability makes it suitable for industry and real-time environmental ap­

plications [45]. Huang et al. demonstrated an E. coli–detecting biosensor fabricated over

graphene matrix. The chemical vapor deposition method was adapted to form a film of

graphene. Over this, antibodies were immobilized. The device showed selective and

sensitive detection of E. coli with a low concentration of 10 cfu/mL. No interference from

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