Fabrication of an organic electrochemical transistor for the detection of Escherichia coli O157:H7 in liquid samples
Creators: Aguilar Vallejo, Angelica Isabel
Publisher: name: University of Alberta Library
Year: 2022

<p>Escherichia coli O157:H7 is an enterohaemorrhagic bacteria which produces Shiga toxins 1 and 2; this strain is responsible for several outbreaks due to contaminated food and water. In order to prevent future outbreaks and maintain the public safe from infections, different microbiological techniques such as cell cultures and polymerase chain reaction (PCR) are routinely used pathogen detection. However, these techniques have some limitations, including the time required for analysis, requirements for sophisticated equipment, and the need for trained personnel. Alternatives that can contribute to the bacteria detection with faster response times and easy methodologies are highly desirable.<br>
Biosensors are devices that can detect a biological analyte by sensing an interaction and transforming it into a measurable output signal. In order to discriminate between the target analyte and other elements found in a sample, high selectivity is required. In this work we propose using the bacteriophage (phage) PP01 as the bioreceptor for the detection of E. coli O157:H7, transducing this interaction by using an organic electrochemical transistor (OECT) as the sensing platform.<br>
In this work OECTs were fabricated using a commercial pre-patterned indium tin oxide (ITO) substrate onto which a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-based active channel was deposited. Different formulations of PEDOT:PSS were explored to develop a stable layer that exhibited high conductivity and good device performance. The organic solvent 2-isopropanol (IPA) was added as conductive enhancement agent, and (3-glycidyloxypropyl)trimethoxysilane (GOPS) was added as a cross-linker to increase the stability of the ink in water.<br>
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Gold gate electrodes were prepared by physisorption and chemical immobilization of phages PP01 through the MUA/EDC/NHS coupling. The chemical coupling and the attachment of phages was characterized through XPS, and the antimicrobial activity was evaluated by exposing the modified samples to E.coli O157:H7 in liquid and solid phase media. As for the gate electrode, the performance of the transistor was evaluated by using (1) a bare gold wire, and (2) a chemically modified gold wire with immobilized PP01 phages.<br>
Output and transfer curves demonstrated that the transistor works as a depletion mode OECTs, where the best performance was observed when using tryptic soy broth as the electrolyte solution rather than phosphate buffered saline (PBS), reaching an OFF state at VG= 1.0 V. For the measurement of different controls (media, target bacteria, non-target bacteria, and phage), transfer properties were measured over a timeframe of 30-60 min, showing that the transistor developed was stable through all measurements at room temperature. Using a gold wire with chemically-attached phage PP01 as the gate electrode, selective detection of E. coli O157:H7 (at a concentration of 108 CFU/mL in TSB medium) was demonstrated. This work aims to set the basis for a new generation of transistors in which phages are used as bioreceptors, and detect the presence of E. coli O157:H7 in liquid samples faster. This would provide a complementary test for the microbiological techniques widely used in water- and foodborne pathogen detection.</p>