**1. Introduction**

Coliforms or bacteria are commonly found in the digestive tracts of animals, humans, plants, and soils. Most coliforms do not cause diseases. However, the existences of "coliforms" with four genera (*Escherichia, Citrobacter, Enterobacter*, and *Klebsiella*) are indeed used as

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indicators to monitor their potential enteric pathogen contamination of waters [1]. One of the hundred strains of the bacterium *Escherichia coli* named *E. coli* O157:H7 is known as one of the most dangerous (for instance, Europe 2011) [2] gram-negative emerging cause of many foodborne and waterborne illnesses [3], bloody diarrhea (hemorrhagic colitis) [4], hemolytic-uremic syndrome (HUS) causing the kidney or renal failure, and hemolytic anemia (loss of red blood cells), which may lead to death, especially in children [5]. *E. coli* microorganisms (width ~ 0.6 μm, length ~ 1.6 μm) [6] produce the Shiga toxin that causes inflammation and secretion of intestinal fluids. Antibiotics and anti diarrheal medicines (such as Imodium) are not recommended for treating *E. coli* O157:H7 pathogenic infections.

Over the years, beside the relatively time-consuming and expensive conventional detection methods (e.g., evaluation of microorganism morphology, counting the bacteria colonies with Violet Red Bile Agar [7] after 72 h, investigations through the polymerase chain reaction (PCR) for amplification of low contents of bacterial nucleic acids), several methodologies with rapid detection using either laboratory instrumental methods (e.g., chromatography, infrared/epi-fluorescence microscopy [8], bioluminescence, flow laser cytometry and immunomagnetic separation [9], fluorimetry [10], etc) or portable, sensitive, and specific devices named biosensors have been reported [11]. Thus, in 1989, Karp's group [12] reported the development of the first biosensor using stable-light-emitting *E. coli* cells. Technically, a biosensor is a self-contained integrated device, which is capable of providing specific quantitative or semi-quantitative analytical information using a biological recognition element (biochemical receptor), which is in direct spatial contact with a transducer element [13]. Today, on the ISI Web of Science are reported more than 1220 publications about different biosensor configurations for the specific and selective detection of *E. coli* bacterial cells.

Biosensors are classified either as bioaffinity sensors when the biological recognition entity is an antigen/antibody (named immunosensors) [14] or a single strain DNA or ssDNA/ RNA sequences (named DNA-/RNA sensors) immobilized onto a solid support via a linker molecule [15] that interact specifically with a target (named the complementary ssDNA-sequence to the ssDNA-probe), enzyme sensors, receptor ligand-binding sensors [16], and whole cell biosensors (named microbial sensors); or in function of the type of used physical transducer in electrochemical, optical, piezoelectric, and calorimetric (bio) sensors.

On the other hand, since early 1997 [17] bioluminescent genetically engineered *E. coli* microorganisms were intensively used as sensitive and friendly bioreporter's tools for screening the genotoxicity and cytotoxicity of various classes of water pollutants, endocrine disruptor's compounds, explosives [17, 18], and nanoparticles [19–22].

**2. Biosensor platforms for the quantification of** *E. coli*

each biofunctionalization step [23].

Optical-based surface plasmon resonance and acoustic quartz crystal microbalance biosensors are known for their analytical performances in terms of label free and real-time detection capabilities, fast and stable response time, and target low detection limits. Furthermore, electrochemical impedance spectroscopy (EIS) label free biosensors are suitable for electrical characterization (such as double layer capacitance, solution resistance, electron transfer resistance, and Warburg impedance) of biocatalytic transformations on electrode surfaces after

**Figure 1.** Optics and electrochemistry connected to smartphones for the detection of *E. coli* bacteria. For instance, an electrochemical system includes an Android cellphone (HTC ONE X), a Bluetooth shield (Seeed SLD63030P), a micro controller (Arduino), a chip for impedance converter network analyzer (AD 5933), and packaged sensor [66]. Also an Xcode (Apple, CA, USA), which allows users to take pictures at the four specific angles of scatter detection (15°, 30°, 45°, and 60°) at a fixed distance is reported [62]. CV—cyclic voltammetry, EIS—electrochemical impedance spectroscopy.

Biosensor Platforms for Rapid Detection of *E. coli* Bacteria

http://dx.doi.org/10.5772/67392

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This chapter presents the latest developments for the detection of *E. coli* strains using electrochemical, optical, and acoustic biosensors and their integration in microfluidic platforms as well as the next generation of portable biosensors using smartphones (**Figure 1**, **Table 1**).

**Figure 1.** Optics and electrochemistry connected to smartphones for the detection of *E. coli* bacteria. For instance, an electrochemical system includes an Android cellphone (HTC ONE X), a Bluetooth shield (Seeed SLD63030P), a micro controller (Arduino), a chip for impedance converter network analyzer (AD 5933), and packaged sensor [66]. Also an Xcode (Apple, CA, USA), which allows users to take pictures at the four specific angles of scatter detection (15°, 30°, 45°, and 60°) at a fixed distance is reported [62]. CV—cyclic voltammetry, EIS—electrochemical impedance spectroscopy.
