Universal Bacterial Detection Utilizing PEDOT:PSS-Based Organic Electrochemical Transistors
Authors: Frantz Eric , Han Daewoo , Steckl Andrew 
Published: July 2021

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 important 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 technique 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 utilizing 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 the 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 a shift in effective gate voltage, leading to a change 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 Luria-Bertani (LB) and Dey-Engley (D/E) media, diluted to different concentrations in broth, and used as the operating media for OECT. Concentrations of 1.9e5 to 6.8e8 CFU/ml were found to cause a shift in effective gate voltage between 36.8 to 97.5mV.

Craun, G.F., Statistics of waterborne outbreaks in the US (1920–1980). Waterborne diseases in the United States, 2018: p. 73-159.

Ahmed, A., et al., Biosensors for whole-cell bacterial detection. Clinical microbiology reviews, 2014. 27(3): p. 631-646.

Strakosas, X., M. Bongo, and R.M. Owens, The organic electrochemical transistor for biological applications. Journal of Applied Polymer Science, 2015. 132(15).

Demuru, S., et al. Flexible Organic Electrochemical Transistor with Functionalized Inkjet-Printed Gold Gate for Bacteria Sensing. 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors, 2019.

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.

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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