Enhancement of Bacteria Detection with an Extended-Gate Field-Effect Transistor (EGFET) by Dielectrophoretic Trapping of Bacteria

Bacterial infections that do not respond to treatment are a leading cause of death worldwide and a major public health threat. For example, the O157:H7 strain of <i>Escherichia coli</i> (<i>E. coli</i>) is considered one of the most dangerous foodborne pathogens. It is crucial to detect pathogenic organisms at an early stage so that appropriate treatment and targeted use of antibiotics can be undertaken. Conventional detection techniques, such as enzyme-linked immunosorbent assay (ELISA) or polymerase chain reaction (PCR) are time-consuming, expensive, and require trained professionals. A method for rapid detection of bacteria that is inexpensive, provides a reliable result, and is easy to use is becoming increasingly important. The development of suitable electronic transducers that provide label-free, low-cost, rapid detection of bacteria is of great interest, as this approach could be extended to the development of handheld devices for point-of-care applications.<br/><br/>In previous work, a detection method based on an extended-gate field-effect transistor (EGFET) was developed for the detection of <i>E. coli</i> K12, a common well investigated apathogenic model strain. The sensing region of the EGFET was functionalized with modified porphyrins containing two different linkers: One linker connects the porphyrin to the electrode surface of the gate, and the other binds bacterial cells to the functional layer via a specific peptide chain. After applying a bacterial suspension onto the functional layer, the cells can thus bind to it. The negative charge on the surface of the cells changes the electrical potential at the electrode surface, which affects the electrical behavior of the EGFET. The presence of bound <i>E. coli</i> cells on the functionalized sensor surface has already been successfully detected¹.<br/><br/>The aim of this research is to concentrate bacteria specifically on the sensor surface of the EGFET by exerting a dielectrophoretic force on the cells in a combined system. The electrokinetic effect of dielectrophoresis (DEP) enables contactless manipulation of biological cells in fluids. DEP utilizes the geometry of electrodes to generate non-uniform high-frequency electric fields that exert an attractive or repulsive force on dielectric particles, inducing movement toward areas of maximum electric field gradient (positive-DEP) or minimum electric field gradient (negative-DEP). DEP is a flexible and versatile method for immobilizing, separating, and concentrating cells and has been successfully optimized for the fixation of bacteria on electrodes in previous work. It will be investigated to what extent the reliability and sensitivity of the sensor can be increased by dielectrophoretically trapping the bacteria on the transistor gate. Furthermore, it is possible to extend the functionality of the sensor with selectivity by combining it with DEP. DEP is capable of selectively separating biological particles by properties such as size, material, and shape, which allows selective detection of a bacterial species from a heterogeneous suspension.<br/><br/><b>Reference:</b> 1. Könemund, L., Neumann, L., Hirschberg, F. <i>et al.</i> Functionalization of an extended-gate field-effect transistor (EGFET) for bacteria detection. <i>Sci Rep</i> <b>12, </b>4397 (2022)<br/><br/><b>Key words: </b>dielectrophoresis (DEP), biosensing, EGFET, porphyrin, <i>E. coli </i>immobilization