transfer. These were termed µPADS. They exhibited sensitive and selective glucose de­

tection in the linear range of 0.1–10 mM with an LoD of 25 µM. Glucose detection was

done in real-time samples of human whole blood and blood serum to check applicability

in the clinical analysis [21]. In another work, a biochip was fabricated for the detection of

kidney ailment biomarker, creatinine. Herein, PDMS substrate-based microchannels were

developed. These were strategically placed over carbon screen-printed electrodes. In

further, these electrodes were chemically modified with a matrix of gold nanostructures

and multiwalled carbon nanotube composite. This metallic-carbon nanotube composite

matrix was used to immobilize the creatinase enzyme. This device gave a linear con­

centration range of 0.01 mM–1mM with LoD as 0.5 µM. No interference from any other

co-existing biochemicals and metabolites was observed. Furthermore, physiological

samples were tested for real-time applications [22].

A continuous lactate monitoring wearable biosensor using a screen-printed approach

was developed by Shitanda et al. PDMS substrate with MdO-1,2-naphthoqui and lactate

oxidize enzyme as a working electrode. A microfluidic, PDMS-based sweat collector was

made to collect the sample. The sensor gave a linear range of 0.3–50 mM with an LoD

0.3 Mm [23]. In another interesting work, Zhang et al. developed a microfluidic biosensor

for the detection of interleukin-8, a biomarker for cancer. The microchip was connected

with two passages via a vertical channel. Antibody against this biomarker was used

for capturing which was immobilized in one of the channels and on the other and, the

channel was used for cell culture. A linear range of 7.5–120 pg/mL was observed. Real-

time tumor cells were used for analysis and the biosensor and the obtained results were

compared to the commercial assay results [24]. Likewise, interdigitated printable elec­

trodes chemically modified with gold nanoparticles were designed by Nunna et al. for

cancer biomarker detection using impedance analysis [25]. A circuit board-based bio­

sensor was developed for detection of cytokine, a cardiac biomarker by Evans et al.

Herein, gold electrodes were employed as working and counter electrodes, Ag/AgCl as a

reference electrode [26]. Using a DNA sequence as a capture bioreceptor over nonporous

beads matrix, tumor biomarker was detected by Caneira et al. Herein, beads were used

for immobilizing the DNA probe. The device gave an excellent LoD of 9.5 pM [27].

In a remarkable work, a microfluidic channel device with multi-walled carbon nanotube-

indium-tin-oxide electrodes modified with probe DNA was used over PDMS substrate for

detection of leukemia by Ghrera et al. This biochip displayed an appreciable linear range

of 1 fm–1µM. A very short response time of about 60 seconds was enough to obtain the

results [28]. Pursey et al. designed array electrodes for the detection of a biomarker for

bladder cancer using DNA as a bioreceptor. Herein, three different bladder cancer detection

DNA biomarkers were detected over a single chip. The device gave a LoD of 250 fM. The

microchannel had a facility of integrating 20 sensors simultaneously for detecting different

DNA sequences. The response time was about 2 minutes [29]. Apart from ailment bio­

markers, biosensors for pathogen detection are also reported in the literature. For example,

Funari et al. prepared a chip for the detection of SARS-CoV-2 antibodies. The PDMS-based

micro biosensor was prepared which gave a LoD of 0.08 ng/mL [30]. An interdigitated

biosensor for detection of Salmonella type B and type D detection was prepared by Liu et al.

The fabricated biosensor was subjected to impedance analysis and the signal was recorded

as a function of bacteria concentration. The antibody-antigen complex approach was used

and the biosensor was selective with zero interference from E. coli strains [31]. Same way,

PDMS-based micro biosensor was fabricated by Jiang et al. using a dendrimer aptamer for

detecting E. coli. [32]. Overall, significant printable and flexible biosensors for health

monitoring have been reported.

Printable and Flexible Biosensors

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