Label-free detection of E. coli by alternating current electrokinetic capacitive sensors

Escherichia coli (E. coli) is one of the most common pathogens in water and foods, and it poses a significant threat to global public health, particularly in low- and middle-income countries. However, most of the state-of-art detection method for E. coli bacteria sensing needs fluorescence staining or pre-immobilizations or specific biomaker as labels before tests, making the detection process a time costing and labor intensitive work. Thus, it is desirable to develop a label-free and no-immobilization detection method for the sensitive detection of E. coli or other pathogens.

In this work, we developed a sensitive method for E. coli detection without any labels or pre-immobilizations. Here the source AC signal provides ACEK effects to trap bacteria onto the electrode surface. As the source AC signal is cut off, the enriched bacteria would release from sensor electrodes. Then, a significant interfacial capacitance change along with particle releasing is observed by applying a measurement AC signal. The DEP capture of E. coli bacteria at different AC frequencies and voltages are experimentally investigated to optimize the performance of capacitive sensors. To note, the total area of our sensitive unit can be as large as 2 mm × 2 mm with the geometry design of isomotive DEP. Capacitive sensing tests of river water collected from local river and tap water with several control groups are performed to show its reliability as a biosensing approach for the sensitive detection of E. coli.

The most significant advantage of this method is that we do not need to pre-immobilize any probes (antigens, or antibodies, etc.) or take incubation onto the sensor electrode before taking capacitance measurement. Moreover, the straight forward operation is pre-immobilization free, and therefore it meets the requirements of on-site bacteria detection for pathogen detection in water quality monitoring or food safety.