**5.1 Immobilization by physisorption, electrostatic bindings and covalent bonding**

Most common approach used for immobilization of phages is physisorption [50, 51]. This approach is very artless, but then again the adsorbed phage may possibly detach as of substrate surface because of shear, changes in pH, or temperature, or ionic concentrations caused in the medium that reduces principally their biosensing applications. Subsequently most phage particles having net negative charge at pH 7 [52], a number of investigators successfully used electrostatic binding for phages immobilization **Figure 4,** [52]. Also this methodology suffers due to variability and bacteriophage detachment in turn to the physico-chemical fluctuations in the analyte medium. Covalent bonding of phages offered a more stronger attachment and is not at risk to easy detachment of phages [53, 54]. Proper chemical studies can make easy selection of suitable substrate and then potential application. Covalent attachment resulted in a sophisticated bacteriophage surface mass that is principally necessary for phage application in biosensor development [55, 56]. To design bioactive surfaces with phages, phage infectivity is important or at least phage should be able to interact with host bacteria or analyte; therefore, optimization is needed to reduce the effect on bacteriophage integrity during immobilization.

#### **Figure 4.**

*Graphical representation of bacteriophage random immobilization and electrostatic, charge-directed orientated immobilization of T2 phage onto CNT electrode surface functionalized with polyethyleneimine (PEI) [57].*

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**Figure 5.**

*Principle and Development of Phage-Based Biosensors DOI: http://dx.doi.org/10.5772/intechopen.86419*

Bacteriophage-display tools can enable scientist to display peptides of choice present on the phage exterior, that is, phage envelope. Phages expressed peptide can consequently be adsorbed on material surfaces that are coated with peptides specific ligands **Figure 5**. Phage-display-libraries are produced by introducing DNA segments into specific phages to facilitate each phage to display a specific peptide expressed by the DNA segment inserted [58]. Technology of phage display developed as a combined influence of two central thoughts, fusion phage and combinatorial peptide libraries [59]. The first theory allows display of external peptides on bacteriophage surface [59]; while the second idea hires libraries of numerous peptides achieved in corresponding production as contrasting to production of single specific peptides [60]. Merging these two theories stemmed progress in phage-display-tools, multibillion clone alignments of self-assembled and self-amplified bio-components [54]. It is significant to keep in mind that genetic alteration may alter the characteristics properties of bacteriophages. For example, biotin-carboxylcarrier-protein (BCCP) gene or the cellulose-binding-module (CBM) gene to the small-outer-capsid-protein (SOCP) gene of T4 bacteriophage was attached, affecting bacteriophage infectivity, and result was decline in burst size, as well

*Current applications of phage display technologies as imaging agents. Icosahedral phages are mostly used as, aiming on moieties for bacterial detection, and substrates for signal amplification. While filamentous phages* 

*are mostly used as multifunctional probes, and a variety of sensors [67].*

**5.2 Phage display technologies**

as extended latent period [61].
