3.1. Polysaccharide biosensor:
Polysaccharides such as alginate, chitin, chitosan, agarose, cellulose, dextran and hyaluronic acid are biomaterials with the unique property of forming hydrogels. These polysaccharide hydrogels are attractive biomaterials for biosensors because of their hydrophilicity, high protein affinity, heavy metal ion chelation, biocompatibility, ease to modify surface chemical group, low cost, acceptable mechanical properties and facile fabrication method.
There is much evidence of application of polysaccharide-based hydrogels as immobilized biomaterial for fabrication of bioreceptors (Tavakoli & Youhong, 2017). Physical absorption, trapping, covalent bonding, crosslinking, and other approaches can be used to immobilize bio receptors on the hydrogel surface. Irreversible immobilization of bioreceptor prevents detachment of it from the biosensor and if it gets detached, the hydrogel microstructure or bio receptor activity will be destroyed (Mousty et al., 2001).
3.1.1 Alginate based Biosensor :
Alginate-based biosensors have applications in the detection of bacterial contamination in milk (Kikuchi et al., 2020), water quality estimation and biomedical applications. To determine glucose level in blood, alginate microsphere glucose oxidase-based biosensor was designed, which utilizes glucose oxidase enzyme to estimate the glucose in vivo glucose monitoring system (Chaudhary et al., 2010). Cell-based Microarray is designed by applying alginate and antibodies for application in drug discovery, toxicology and stem cell research. Alginate-based 3D microarrays are developed for pancreatic cancer detection (Fernandes et al., 2008; 2009).
Additional evidence has been found for the detection of heavy metals byAliivibrio fischeri in water, based on alginate microsphere Luminescence Fiber-Optic Biosensor (Futra et al., 2014). The A. fischeri bacteria could maintain their metabolic activity for a longer time, without any change in bioluminescence. A low limit of detection for heavy metals, such as copper, cadmium, plum, chromium, gold, cobalt and nickel, may be observed using an alginate-based biosensor ranging from 1:56 μg/L to 3100 μg/L.
Turemis et al. (2018) employed a Calcium-alginate fluidic flow cell with built-in detector Chlorella volgaris and the Tetrahymen pyriformis algae to estimate marine contaminants in real-time, using fluorescent photosynthetic photosystem II analysis. The other algal species Laminaria hyperborean pyeroalginate conjugate biomaterial was used for physical entrapment of polyphenol oxidase (PPO). These amperometric biosensors can be used for determining catechol as analyte, producing the sensitivity of 80 and 350 µA M-1 cm-2, respectively (Abu-Rabeah et al., 2005).
3.1.2 Chitin and chitosan biosensor:
Chitin and chitosan hydrogels are biocompatible and easy to modify chemically. There are 5 categories of the chitin-based biosensor (Kittle et al., 2012).