## 5 Types of Phage-Based Biosensors
### Phase-Based Electrochemical Biosensors
#### 5.2.1 Amprometric Biosensors  
Phage-based amperometric biosensors are one of the electrochemical sensors that have received much attention due to their simplicity, high sensitivity, specificity, and suitability for field testing. However, inhibitors can interfere with the assay and lower its specificity. In this platform, the phages are used either as a probe for the detection of a target bacterium or as a lysing agent for the indirect detection of pathogens using the metabolites released from the lysed cells [25]. Amperometric biosensors have been developed to quantify the flow of the current between electrodes when the oxidation-reduction reaction takes place. In this assay, enzymes such as horseradish peroxidase (HRP), glucose oxidase, and alkaline phosphatase (AP) are used as bio-receptors [109].  
Several phage-based amperometric biosensors have been introduced for the detection of foodborne bacterial pathogens from food surfaces. [PERSON] et al. designed phage-based amperometric techniques (specifically, \(\beta\)-D-galactosidase) for the detection of _E. coli_ at concentrations as low as 1 CFU/100 mL within 6 to 8 h [33]. Likewise, [PERSON] et al. used the same platform to detect M. _smegmatis_ and _B. cereus_ using \(\beta\)- and \(\alpha\)-glucosidase, respectively, as markers with a detection limit of 10 CFU/mL within 8 h [34]. [PERSON] et al. designed a T4 phage-based sensor with a micro-gold electrode for the detection of _E. coli_ from unspecified food samples. The sensitivity of this amperometric biosensor is in the range of 1.9 \(\times\) 10\({}^{1}\)-1.9 \(\times\) 10\({}^{8}\) CFU/mL of the bacterial cells [25].  
[PERSON] and [PERSON] developed a portable sandwich-type phage-based amperometric biosensor using the environmental phage isolates belonging to the _Myovitirade_ and _Siboviridae_ families. The sensor was highly specific to various Shiga toxin-producing _E. coli_ (STEC) serogroups. The amperometric biosensor showed a detection limit of 10-10\({}^{2}\) CFU/mL for the STEC O26, O157, and O179 strains within 1 h [15]. In another study, [PERSON] et al. introduced a quick and inexpensive bacterial detection platform using T6 bacteriophages in combination with ion-selective field-effect transistors (ISFETs) and potassium-sensitive  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Transducer** & **Host Bacterium** & \begin{tabular}{c} **Bio-Receptor** \\ **(Phage)** \\ \end{tabular} & \begin{tabular}{c} **LOD** \\ **CFU/mL** \\ \end{tabular} & **Assay Time** & \begin{tabular}{c} **Food** \\ **Samples** \\ \end{tabular} & **Ref.** \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} QCM-based \\ assays \\ \end{tabular} } & _Salmonella Typhimuriumium_ &
\begin{tabular}{c} Filamentous \\ phage \\ \end{tabular} & \(10^{2}\) & 3 min & NR & [102] \\ \cline{2-6}  & _M. tuberculosis_ and & D29 & \(10^{3}\) & NR & NR & [103] \\ \cline{1-1}  & _S. aureus_ & 12,600 & \(10^{4}\) & NR & NR & [104] \\ \cline{1-1}  & _E. coli_ & T4 & NR & NR & Milk & [16] \\ \cline{1-1}  & _E. coli_ K12 & Wild type & \(10^{3}\) & NR & NR & [105] \\ \hline \hline \end{tabular}  
* NR—not reported.  
\end{table}
Table 1: _Cont._membranes (potassium ion detection). This amperometric platform was highly specific for the detection of _E. coli_ in less than 10 min [110].