Development of a paper-based electrochemical immunosensor using an antibody-single walled carbon nanotubes bio-conjugate modified electrode for label-free detection of foodborne pathogens

The need for low-cost, sensitive, and reliable sensors for the detection of whole bacterial cells in food samples without pre-treatment has been increasing. Outbreaks of foodborne diseases can be severe, especially in developing countries; however, most bio-detection tools are unaffordable. Here, we have developed a rapid and low-cost paper-based electrochemical immunosensor for label-free detection of Staphylococcus aureus, using antibody (Ab)-single walled carbon nanotube (SWCNT) bio-conjugates. Anti-S. aureus antibodies were covalently attached onto the SWCNTs, using the N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide coupling reagent. These Ab-SWCNT bio-conjugates were then immobilized on the working electrode, and the presence of S. aureus was detected by analyzing the change in peak current following antigen-antibody complex formation. Differential pulse voltammetry was performed with a bacterial concentration ranging from 10 to 107 colony forming units (CFU) mL−1. A selectivity assay using Escherichia coli B, Bacillus subtilis, and S. epidermidis (to examine cross-reactivity) showed that the sensor was specific to S. aureus. Moreover, this immunosensor showed a good linear relationship (R2 = 0.976) between the increase in peak current and logarithmic S. aureus concentration, with a rapid detection time (30 min) and a limit of detection of 13 CFU mL−1 in spiked milk samples. This low-cost immunosensor can be used for rapid detection of pathogens in actual food samples with high sensitivity and specificity.