Immunosensors biosensors

The development of immunosensors is one of the most active research areas in immun-odiagnostics. A large number of immunosensors, which combine the sensitivity and specificity of immunoassays with physical signal transduction, have been developed 

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Electrochemical behavior of nanomaterials as transducer for biosensors, immunosensors and chemical sensors. 

Key words Electrochemical biosensors, Gold nanoparticles, Enzyme biosensors, Immunosensors, Composite electrodes, Carbon nanotubes. 

In this application, the conducting polymer serves as the chemically-sensitive film that transduces an immunoassay into an electrical signal. A major advantage in using conducting polymers for immunoassay-based biosensors (immunosensors) is that antibodies can be coated directly onto the active polymer surface with little degradation of antibody functionality. 

Genosensors [deoxyribonucleic acid (DNA)-based biosensors], immunosensors, cytosensors, and aptamer-based biosensors (aptasensors) are types of affinity-based biosensors. 

The formation of PPy on an electrode surface provides a nanoporous matrix that is highly used for the immobilization of biomolecules to design various biosensors (electrochemical biosensor, immunosensor, and DNA sensor). It also acts as a mediator to transfer the analytical signal generated by some redox enzymes to the transducer even if the redox center is deeply buried in the protein globule. In addition, it is an efficient protector of electrodes against interfacing materials (proteins present in real samples such as blood and urine). 

The techniques that are currently used by most laboratories to measure cyt c release include ELISA, Western blot, and flow cytometry (Kim et al., 2007 Ott et al., 2002 Christensen et ah, 2013 Adachi et al., 2004). Despite providing high sensitivity and selectivity, these traditional analytical methods stiU have some drawbacks, such as time-consuming, sophisticated, expensive equipment, limitations in colored sample analysis, and the demand for skilled professionals. To minimize limitations imposed by traditional methods, electrochemical biosensors/immunosensors combined with the high specificity of conventional methods also present several advantages including the possibility of point-of-care testing development. 

Fig. 8. Basic components of a biosensor. In the case of an immunosensor, the antibody (or antigen) would be immobilized onto the transducer.

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

Electrogenerated chemiluminescence (ECL) has proved to be useful for analytical applications including organic analysis, ECL-based immunosensors, DNA probe assays, and enzymatic biosensors. In the last few years, the electrochemistry and ECL of compound semiconductor nanocrystallites have attracted much attention due to their potential applications in analytical chemistry (ECL sensors). 

The current trend in analytical chemistry applied to evaluate food quality and safety leans toward user-friendly miniaturized instruments and laboratory-on-a-chip applications. The techniques applied to direct screening of colorants in a food matrix include chemical microscopy, a spatial representation of chemical information from complex aggregates inside tissue matrices, biosensor-based screening, and molec-ularly imprinted polymer-based methods that serve as chemical alternatives to the use of immunosensors. 

The material is presented in 17 chapters, covering topics such as trends in ion selective electrodes, advances in electrochemical immunosensors, modem glucose biosensors for diabetes management, biosensors based on nanomaterials (e.g. nanotubes or nanocrystals), biosensors for nitric oxide and superoxide, or biosensors for pesticides. 

Biosensors may be classified into two categories biocatalytic biosensors and bioaffinity biosensors. Biocatalytic sensors contain a biocatalyst such as an enzyme to recognize the analytic selectively. Bioaflinity biosensors, on the other hand, may involve antibody, binding protein or receptor protein, which form stable complexes with the corresponding ligand. An immunosensor in which antibody is used as the receptor may represent a bioaflinity biosensor. 

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