**1. Introduction**

Many pathogenic bacteria like *Streptococcus*, *Mycobacterium*, *Pseudomonas*, *Salmonella*, *Shigella*, etc. are causing different diseases in humans, resulting in several outbreaks and epidemics of diseases worldwide. Every year, millions of individuals get infected by these bacteria, while the common sources of infections are clinical, foodborne, airborne, and/or waterborne [1]. Clinical, food, and environmental contaminations are the eternal challenges worldwide in the healthcare systems and food safety and environmental monitoring. Irrespective of comprehensive struggles to fight such pathogenic bacteria, the numbers of clinical, food, and environment-related diseases are increasing every year [2]. As a solution to the problem, the development of biosensors especially phage-based biosensors for bacterial detection in clinical, food, and environmental samples has remained a hot topic since the last few decades. Phages in biosensor proved themselves as unique bio-probes, owing to their selectivity, specificity, and

withstanding harsh environmental conditions. Establishing phage-based biosensors for application in food safety and environmental monitoring is a motivating and interesting research topic and is the urgent need of this modern era. The key point is to enhance phage-based cheap recognition tools with maximum levels of selectivity, consistency, and sensitivity with minimum times of assay. Significant struggles have been dedicated on enhancing the transducer surface of biosensor for improved detection and sensitivity. Phage-based bio-probes have been used in transducer development for several analytical approaches to offer specific and selective detection. Bacteriophages as a bioprobe have been successfully applied for bacterial detection in clinical samples (urine) [3], food samples (milk, tomatoes) [4], and environmental samples (river water) [5]. Furthermore, different analytical approaches relying on phage-based bio-probes have been reported like electrochemical [6], bioluminescence [7], fluorescence [8], mass spectrometry [9], magnetoelastic [4], surface plasmon resonance [10], lateral flow assay [11], etc. In the following context, we will review biosensor transduction platforms involving phage-based probes for transducer development to detect infectious bacteria in the field of food and environmental safety monitoring [12]. In this chapter we will highlight applications of different phage-based analytical approaches for bacterial detection in clinical, food, and environmental samples.
