Universal Bacterial Detection Utilizing PEDOT:PSS-Based Organic Electrochemical Transistors
Authors: Frantz Eric , Steckl Andrew 
Published: May 2020

Bacteria are one of the most common sources of illness, responsible for a wide range of infections. Bacterial infections can be caused from a variety of sources, with thousands of deaths attributed to waterborne outbreaks alone [1]. Detection of both infectious and non-infectious bacteria is utilized to ensure commercial goods and water are safe for consumers. Current detection of bacterial contamination typically uses cell culture plates to measure the number of colony forming bacteria (CFU/ml) in a liquid media. This technique is widely used due to its high sensitivity and easy visual readout. Unfortunately, culture counting techniques is time consuming (1-3 days), requires skilled lab technicians, can be contaminated during preparation, and cannot be integrated into the desired testing media directly.
To overcome these limitations, many bacterial sensors and detection techniques have been developed over the last few decades [2]. A recent sensor for bacteria detection is the organic electrochemical transistor (OECT). OECTs are polymer-based transistors that utilize ionic solutions to de-dope and re-dope a conducting channel. These devices are known for their high transconductance, bio-compatibility, low operating voltage, low cost, small size, ease of integration into measurement systems, and ability to function in aqueous environments [3]. Detection of a single bacteria is typically desired and achieved through the capture of bacteria cells onto the OECT channel area [4]. This approach allows for rapid detection of a specific pathogen with high sensitivity. However, for detecting contamination from a variety of bacteria a different approach must be used.
We have investigated the OECT response to the presence of non-captured bacteria present within the OECT operating media. In this approach cells are detected both in solution and on the surface of the source-drain channel and on the gate electrode. Presence of bacteria between the gate and channel region will cause an increase in effective gate voltage, resulting in a decrease in source-drain current. Detection and characterization of (non-bacteria) whole cells has previously been reported utilizing this approach [5, 6]. In our work we have focused on the bacteria pseudomonas fluorescens (p. fluorescens) due to its size (~1µm) and potential as a water borne pathogen. P. fluorescens was cultured in LB media, diluted to three different concentrations, and used as the operating media for OECT. Concentrations of 8.7e12, 8.7e11, and 8.7e10 CFU/ml were found to shift source-drain current by 16.1, 13.8, and 12.3µA, respectively. From this data a present lower limit of detection for the sensor is estimated to be ~5.0e4 CFU/ml.
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3. Strakosas, X., M. Bongo, and R.M. Owens, The organic electrochemical transistor for biological applications. Journal of Applied Polymer Science, 2015. 132(15).
4. Demuru, S., et al. Flexible Organic Electrochemical Transistor with Functionalized Inkjet-Printed Gold Gate for Bacteria Sensing. in 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII (TRANSDUCERS & EUROSENSORS XXXIII). 2019. IEEE.
5. Liao, J., et al., Organic electrochemical transistor based biosensor for detecting marine diatoms in seawater medium. Sensors and Actuators B: Chemical, 2014. 203: p. 677-682.
6. Ramuz, M., et al., Monitoring of cell layer coverage and differentiation with the organic electrochemical transistor. Journal of Materials Chemistry B, 2015. 3(29): p. 5971-5977.

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