An Extended-Gate Field-Effect Transistor as a Highly Sensitive Biosensor to Detect Bacteria

The detection of bacteria requires full-fledged qualified employees to prepare individual samples for corresponding machine-based analysis. This process is highly time-consuming and cost-intensive. Therefore, there is a great demand for more rapid, portable, and cost-effective sensors for the detection of bacteria.<br/>For this, well-established electrical measurement methods might be transferred to the investigation of biological systems. Our approach is the development of an extended-gate field-effect transistor (EGFET) as a biosensor. The EGFET is composed of a standard metal-oxide semiconductor field-effect transistor (MOSFET) and a physically separated but electrically connected sensor unit produced as a thin-film device.¹ The connection is realized by extending the MOSFET’s gate electrode into the sensor unit. The potential of the gate-electrode is regulated by the electrical impact of the sensor unit on the MOSFET which further gates the measurable current between its drain and source electrode. The main constituent of the sensor unit is a suspension containing the bacteria of interest, which connects the extended-gate with a control-gate electrode. Both electrodes are functionalized with A₂BC-type porphyrins to link the bacterial cells to the electrode surfaces to shift the electrical potential of the extended-gate electrode on the gate-solution interface.² Different optical and electrochemical methods verified clearly the successful formation of the functional layer. Further, the successful linkage of bacteria on the functionalized electrode were analyzed by fluorescence lifetime imaging microcopy (FLIM).³ The transfer characteristic of the EGFET also clearly indicated the impact of trapped bacterial cells due to lower potential values on the extended-gate electrode.¹ However, our latest results indicate a non-homogeneous coverage of the electrodes by the bacteria.³<br/>Further investigations focus on the increase of trapped bacteria to improve the sensitivity of the biosensor. Here, one of our approaches is the integration of dielectrophoresis (DEP) to the electrodes of the sensor unit. DEP is a highly flexible and multifunctional method to immobilize, separate, and concentrate biological particles such as whole cells but also dissolved molecules in a liquid. In addition, an optimized measurement setup or different functional layers based on e.g. boron-dipyrromethene (BODIPY) might also improve the sensitivity. The synthesis of BODIPYs compared to the A₂BC-type porphyrins are less complex which fulfills the requirement of a lean device.<br/> <br/>¹Könemund, L., Neumann, L., Hirschberg, F. et al. Functionalization of an extended-gate field-effect transistor (EGFET) for bacteria detection. Scientific Reports 12, 4397 (2022).<br/>²Minamiki, T., Minami, T., Sasaki, Y., et al. An Organic Field-effect Transistor with an Extended-gate Electrode Capable of Detecting Human Immunoglobulin A, Analytical Sciences 31, 725-728 (2015).<br/>³Neumann, L., Könemund, L., Rohnacher, V., et al. A₂BC-Type Porphyrin SAM on Gold Surface for Bacteria Detection Applications: Synthesis and Surface Functionalization. Materials 14, 1934 (2021).