Purpose: Therefore, an impedance aptasensor based on the use of magnetic nanobeads for separation and screen-printed interdigitated electrode for measurement was developed for the rapid detection of E. coli O157:H7 in food products.
Methods: Streptavidin coated magnetic nano-beads (MNBs) (150 nm) were functionalized with biotinylated E. coli-aptamers, and then were mixed with samples containing E. coli O157:H7. A magnetic separator was applied to isolate and concentrate the captured target bacteria. Concanavalin A-glucose oxidase (Con A-GOx) complex was employed as an amplifier to form E. coli-Con A-GOx sandwich through Con A-glycan interaction. The yielded sandwich complex was then transferred to a glucose solution to trigger an enzymatic reaction to produce gluconic acid, which ionized to increase the ion strength of the solution, thus decreasing the impedance on a screen-printed interdigitated electrode. By measuring the impedance change (DZ) over a 30-min reaction, the correlation of DZ with the concentration of E. coli was determined.
Results: Our results showed that the developed aptasensor was capable of specifically detecting E. coli O157:H7 within 1.5h, and can detect as low as 200 microbial cells in a 200 µl sample (103 CFU/ml). Ongoing researches focus on the target bacteria in different foods and a prototype of the instrument.
Significance: This provides a practical method for rapid, sensitive, and on-site detection of E. coli O157:H7.