Single walled carbon nanotube-based junction biosensor for detection of Escherichia coli

Abstract

Foodborne pathogen detection using biomolecules and nanomaterials may lead to platforms for rapid and simple electronic biosensing. Integration of single walled carbon nanotubes (SWCNTs) and immobilized antibodies into a disposable bio-nano combinatorial junction sensor was fabricated for detection of Escherichia coli K-12. Gold tungsten wires (50 µm diameter) coated with polyethylenimine (PEI) and SWCNTs were aligned to form a crossbar junction, which was functionalized with streptavidin and biotinylated antibodies to allow for enhanced specificity towards targeted microbes. In this study, changes in electrical current (ΔI) after bioaffinity reactions between bacterial cells (E. coli K-12) and antibodies on the SWCNT surface were monitored to evaluate the sensor's performance. The averaged ΔI increased from 33.13 nA to 290.9 nA with the presence of SWCNTs in a 10(8) CFU/mL concentration of E. coli, thus showing an improvement in sensing magnitude. Electrical current measurements demonstrated a linear relationship (R2 = 0.973) between the changes in current and concentrations of bacterial suspension in range of 10(2)-10(5) CFU/mL. Current decreased as cell concentrations increased, due to increased bacterial resistance on the bio-nano modified surface. The detection limit of the developed sensor was 10(2) CFU/mL with a detection time of less than 5 min with nanotubes. Therefore, the fabricated disposable junction biosensor with a functionalized SWCNT platform shows potential for high-performance biosensing and application as a detection device for foodborne pathogens.

Figure 1. Sensor design and set-up.

(A) Schematic of the single junction sensor device. Inset: FESEM image of junction. (B) Experimental configuration for electrical measurement using a junction sensor. (C) Illustration of E. coli captured on functionalized junction.

Figure 2. FESEM images of the sensor's microwire electrodes.

(A) Bare microwire surface in comparison to (B) a surface coated with a PEI-SWCNT composite layer at 500 nm. (C) Modified surface with E. coli cells bound to immobilized antibodies at 1 µm.

Figure 3. Electrical current response to step-wise modification of junction sensor.

(A) I-V curve from 0 to 1 V_DC corresponding to individual sensor modification layers. (B) Effect of SWCNTs on signal response during functionalization and detection at 1 V_DC. (C) Averaged change in current in response to captured E. coli for sensors with and without SWCNTs. E. coli concentration was 10⁸ CFU/mL.

Figure 4. Linear relationship between changes in current and concentrations of E. coli (10²–10⁵ CFU/mL) bound to the functionalized junction sensor.

Figure 5. Relative response of the junction sensor to E. coli (10⁴ CFU/mL) and S. aureus (10⁴ CFU/mL).