## 6 Conclusions and Future Directions  
Bacteriophages have very important characteristics that make them ideal biorecognition agents for incorporation into biosensors for the detection of foodborne bacterial pathogens in food samples. They are highly specific; therefore, phage-based sensors are unaffected by background flora. As phages infect only living host bacteria, a phage-based sensor can easily distinguish living from dead organisms. The resistance of phages and phage-associated proteins to a wide range of temperatures, pH values, and organic solvents makes phage-based biosensors superior to other conventional pathogen-detection techniques. Generally, bacteriophage-based biosensor systems are cost-effective, specific, and more stable than conventional foodborne pathogen detection techniques. Unlike antibodies, bacteriophages can be produced in large quantities readily; thus, the fabrication of a biosensor using whole phages or phage proteins could be a cost-effective economical platform [137]. Currently, new phages with multiple binding sites on their surface or with other desirable properties can be generated using advanced synthetic biology approaches. This enables phages to be used for a wide range of biosensor applications [12]. With all the advantages mentioned above, there are certain challenges related to the development of phage-based biosensors that need attention. An obvious challenge of phage-based biosensors is the employment of bacteriophages that have a broad host range in a manner so that false-negative results can be avoided. Bacteriophages typically detect a specific receptor on the host cell's surface; therefore, phage-based sensors must be tested against target and nontarget bacteria to diminish the chance of false-negative results. Besides, bacterial contamination or the presence of lipids, carbohydrates, and proteins could profoundly affect the binding efficiency and phase immobilization on the sensor surface. In addition, phage resistance is an emerging challenge due to the lack of receptors on the surface of the host organism required for phage adsorption, or host resistance triggered by eliciting intracellular defense mechanisms. This phenomenon can also affect the development of phage-based biosensors. However, such a problem can be overcome by using a \"phage cocktail\" containing a mixture of phages. The idea of a phage cocktail has to be adopted in future phage-based biosensor application platforms, especially for the simultaneous detection of multiple foodborne pathogens [14]. Another challenge for the establishment of a stable phage-based biosensor is the formation of stable chemical bonds between the surface of the biosensor and the phage attachment domain. For this, the physical as well as chemical features of the phages have to be explored in-depth to continue with suitable reactions to generate a stable sensor platform [138]. In addition, it has been recognized that when phage-based biosensors are exposed to a dry environment, the tail fibers lose their structural integrity, affecting bacterial capture on the sensor platform [52]. Nevertheless, engineered phage-based biosensors can circumvent these limitations. Engineering bacteriophages is inherently challenging due to the compact nature of the genomes and the availability of fewer noncoding sequences or restriction sites. However, with the development of numerous DNA synthesis methodologies and their application in synthetic biology, these drawbacks are likely to fall away rapidly. Hence, even with the development of synthetic biology, there is still a need for more insight into the genetic makeup of phage genomes that can be used for this purpose [138]. The selection of bacteriophages of a desired size, especially for nano-biosensor platforms, and the optimization of the expression of the binding domains on the surface of the phages remain the major challenges.