**4.6 Applications of biosensor**

Biosensors are equipment to transform biological, physical, and chemical indications of biological schemes into electrical by classifying particular responses to aim analyses [136]. A blood glucose biosensor is a typical sample of a characteristic biosensor that uses the enzyme Glucose oxidase. Electrochemical biosensors particularly react with target moieties and produce an electrical signal linked to particular analyze concentrations, pH, and temperature [137]. Biosensors are a vital role in tissue engineering, and also chitosan nanocomposites are well worn in these kinds of applications. Generally, metal nanoparticles display higher conductivity and electronic features than transmission polymer, however, the flexibility of the polymer creates them matchless for numerous applications. The addition of transmission

#### **Figure 6.**

*Stepwise schematic of the nanosystem synthesis: MCM-41 was prepared through a surfactant-assisted sol-gel method, then, the fabricated chitosan-curcumin nanoparticles (CSNPs) were crosslinked onto MCM-41 through TPP (MCM@CS). In the next step, the synthesized AuNPs were modified physically onto the MCM-41 surface as well as loaded into CSNPs networks (MCM@CS@Au), and MUC-1 aptamer as a targeted agent linked to AuNPs via sulfuric bonds (MCM@CS@Au-Apt); eventually curcumin was loaded into the final nanosystem (MCM@CS@Au-Apt (CUR)) [147] (Esmaeili Y, Khavani M, Bigham A, Sanati A, Bidram E, Shariati L, Zarrabi A, Jolfaie NA, Rafienia M. Mesoporous silica@chitosan@gold nanoparticles as "on/off" optical biosensor and pH-sensitive theranostic platform against cancer. Int J Biol Macromol. 2022 Mar 31;202:241–255).*


#### **Table 1.**

*Chitosan-based biosensor applications.*

nanoparticles to chitosan materials increases the nanocomposite electrical conductivity on top of stimuli-responsive features that could be used for sensing biological types [138]. For particularly improving the sensitivity to biological moieties, biosensor faces have been changed using enzymes similar to cholesterol esterase [139] and cholesterol oxidase [140] to determine cholesterol substance in the blood or human serums. As it is seen chitosan nanocomposites-based biosensors are higher efficient, sensitive, and durable in comparison to pure chitosan [138]. A lot of nanostructured inorganic materials for instance cuprous oxide nanoparticles [141] and Fe3O4 nanoparticles [142]. NiFe2O4 nanoparticle [143], Cerium oxide nanoparticle [144], and TiO2 nanoparticles [145] are often used to increase the electronic features, moreover, the chitosan electrical conductivity-based materials in nanocomposites [146].

In another study, Esmaelili *et al.* developed a multifunctional nanosystem of mesoporous silica@chitosan@gold-aptamer (MCM@CS@Au-Apt) encapsulated curcumin for MUC-1 positive tumor cells targeting and drug delivery (**Figure 6**). They found that MCM@CS@Au has "on/off" fluorescence bio-sensing ability with selective performance against MUC-1 positive tumor cells

**Table 1** showed chitosan-based biosensor applications in the recent years
