ABSTRACT
The requirement to prevent foodborne illnesses underscores the need for reliable detection tools, stimulating biosensor technology with practical solutions for in-field applications. This study introduces a low-cost immunosensor based on a single-walled carbon nanotube (SWCNT)-modified gold leaf electrode (GLE) for the sensitive detection of Escherichia coli. The immunosensor is realized with a layer-by-layer (LbL) assembly technique, creating an electrostatic bond between positively charged polyethylenimine (PEI) and negatively charged carboxyl-functionalized SWCNTs on the GLE. The structural and functional characterization of the PEI-SWCNT film was performed with Raman spectroscopy, high-resolution scanning electron microscopy (HRSEM), and electrical measurements. The PEI-SWCNT film was used as a substrate for antibody immobilization, and the electrochemical sensing potential was validated using electrochemical impedance spectroscopy (EIS). The results showed a wide dynamic range of E. coli detection, 101-108 cfu/mL, with a limit of detection (LOD) of 1.6 cfu/mL in buffer and 15 cfu/mL in the aqueous solution used for cleansing fresh lettuce leaves, affirming its efficiency as a practical and affordable tool in enhancing food safety.
ABSTRACT
Single-walled carbon nanotubes (SWCNTs) are well-known for their excellent electrical conductivity. One promising application for SWCNT-based thin films is as transparent electrodes for uncooled mid-IR detectors (MIR). In this paper, a combination of computational and experimental studies were performed to understand the chemistry behind the stability of carboxylic SWCNTs (SWCNTs-COOH) dispersions in different solvents. A computational study based on the density functional tight-binding (DFTB) method was applied to understand the interactions of COOH-functionalized carbon nanotubes with selected solvents. Attention was focused on understanding how the protonation of COOH groups influences the binding energies between SWCNTs and different solvents. Thin film electrodes were prepared by alternately depositing PEI and SWCNT-COOH on soda lime glass substrates. To prepare a stable SWCNT dispersion, different solvents were tested, such as deionized (DI) water, ethanol and acetone. The SWCNT-COOH dispersion stability was tested in different solvents. Samples were prepared to study the relationship between the number of depositions, transparency in the MIR range (2.5-5 µm) and conductivity, looking for the optimal thickness that would satisfy the application. The MIR transparency of the electrode was reduced by 20% for the thickest SWCNT layers, whereas sheet resistance values were reduced to 150-200 kΩ/sq.
