2. Spectroscopic: These give the chemical composition, hybridization, and func­

tional group information. Techniques like Raman, UV-Vis, FT-IR, and NMR are

commonly used techniques. These studies also give plausible bond formations

amongst the various modified layers.

3. Morphological/Elemental analysis: To find out the surface characteristics, di­

mensions, size, shape, and presence of elements in the biosensors matrices,

techniques like XRD, XPS, BET, and EDX are used. The metallic and non-metallic

elements have a significant role in enhancing the enzyme activity.

22.1.3 Printable and Flexible Biosensor Fabrication

Printable and flexible biosensor devices are fully integrated, portable, and use low

sample and reagent volume for analysis. Hence, these can be employed as a point-of-

care testing tool (POCT). Detection of biomarkers, pathogens, and other health para­

meters can be carried out using these biosensors. These give rapid results with no

sample preparation and are hence easy to use. In further, these types of biosensors are

robust, highly selective, and cost-effective. Several approaches are being adapted for

their fabrication like 3D printing, ink-jet printing, screen printing, lamination, molding,

embossing, photolithography, soft lithography, and laser cut. Each approach is de­

scribed briefly [13,14]:

1. 3D printing (or additive manufacturing) is an approach in which conductive fi­

laments are deposited layer-by-layer giving a 3D structure. Computer aided

design (CAD) software is used for designing the sensor. Filaments like acrylo­

nitrile butadiene styrene (ABS), poly lactic acid (PLA), etc. are used. Various

types of 3D printers like fused deposition molding (FDM), extrusion, lamination,

stereolithography, and photo-polymerization are used.

2. Molding: Liquid polymers are molded and solidified as a sensor. There are two

ways for this: (a) injection molding and (b) replica molding. Figure 22.5a shows

injection molding schematic. Figure 22.5b gives replica molding. Herein, the li­

quified polymer is filled in the mold fabricated. This polymer acquires the shape

of the mold that has the desired pattern and upon solidification gives a device.

3. Photolithography: An optical beam like UV, x-ray, electron beam, or ion beam

are used to make the desired electrode patterns over the substrate. A mask with

the desired microchannel or electrode pattern is placed over the substrate and the

optical beam is exposed. The pattern is drawn over the substrate. Figure 22.5c

gives a schematic of this method.

4. Soft-lithography: Molten polymers like polydimethylsiloxane (PDMS), poly

(methyl methacrylate (PMMA), and polyimide are poured over a master mold

of elastomers. These master molds are made up of materials like silicon. The

molds have desired shape, pattern, and channel. The molten polymer tends to

acquire this. Solidification gives the designed sensor. Figure 22.5d is the

schematic representation of this method.

5. Lamination: In this, separate cut layers of materials like glass slides, PMMA,

PLA, etc. are used, stacked, and bonded together. There are three layers: bottom,

intermediate in which microchannels are engraved, and top layer. Adhesives are

used for firm bonding and knife plotter or laser are used for designing.

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Bioelectronics