Single walled carbon nanotube-based multi-junction biosensor for detection of foodborne pathogens

Abstract

Rapid identification of bacterial pathogens in food is urgently needed to ensure food safety. Current detection methods do not meet industrial demands in terms of performance, time, cost, and simplicity. In spite of significant progresses, the development of a sensitive biosensor for practical applications remains a challenge. In this study, a single walled carbon nanotube-(SWCNT) based junction sensor was designed as an alternative detection method for food borne pathogens. Gold tungsten wires (Ø: 50 μm) coated with polyethylenimine (PEI) and SWCNTs were aligned to form a crossbar junction functionalized with streptavidin and biotinylated antibodies. By coating the wires' cross section with bio-nano materials, a sandwich of layered SWCNTs and biomolecules creates a bio-nano junction when targeted bacteria bind and form immune complex reactions. The parallel SWCNT platform layers convert the molecular binding events at the junction into measurable electrical current signals. As a result, changes in electrical current (ΔI) after bioaffinity reactions between bacterial cells and antibodies on the SWCNT surface were monitored to evaluate the sensor's performance. Escherichia coli K-12 and Staphylococcus aureus were used as target microorganisms for single and multi-analyte detection. The SWCNT-based sensing platform generated a ΔI signal response seven-folds higher in a high concentration of E. coli (108 CFU/mL), than compared to a junction sensor without SWCNTs. Thereby, an improvement in sensing magnitude was achieved with SWCNTs. Electrical current measurements from the single junction sensor demonstrated a linear relationship (R2 = 0.973) between the changes in current and concentrations of E. coli in range of 102-105 CFU/mL with a detection limit of 103 CFU/mL and a detection time of 2 min. The design of a portable 2 x 2 multi-junction sensing array demonstrated an improved sensitivity with a 102 CFU/mL limit of detection for E. coli (R2 = 0.978) and S. aureus (R2 = 0.992). Microbial cocktail samples of E. coli and S. aureus showed similar measurement trends for multiplexed detection in 10 μL and 100 μL batch samples. Therefore, the developed label-free SWCNT-based multi-junction biosensor shows potential as a sensitive and simple device with portable and multiplexed applications.