Majid Arvand

Foodborne pathogenic bacteria can cause food poisoning or infection, leading to disease. Early screening of foodborne pathogens has become crucial for managing and preventing these diseases. Here, we developed an electrochemical aptamer-based biosensor to detect Escherichia coli (E. coli O157:H7) in real samples. The glassy carbon electrode (GCE) underwent an initial treatment using a nanocomposite made of reduced graphene oxide (rGO) and gold nanoparticles (AuNPs) (AuNPs/rGO/GCE) to enhance the surface area and boost the sensor’s sensitivity. In addition to good electrical properties, nanocomposites made of rGO and AuNPs play a crucial role in sensor development by enabling high loading and adequate immobilization of biorecognition elements like aptamers while preserving their activity and affinity. Next, to elevate the specificity of the altered electrode, aptamers were linked to the exterior of the prepared electrode (APT/AuNPs/rGO/GCE). The prepared electrode underwent characterization using field emission scanning electron microscopy, energy-dispersive spectroscopy, Fourier-transform infrared spectroscopy, and electrochemical impedance spectroscopy. This proposed aptasensor can accurately identify E. coli O157:H7 within a range of 6 to 6 × 10⁸ CFU/mL and has a detection limit of 3.25 CFU/mL. Microbial culture results validate the aptasensor findings, providing quicker results and a lower detection limit.

In this research, a magnetic nanocomposite, walnut shell@Fe3O4, was synthesized as a natural adsorbent for the removal of Coomassie Brilliant Blue (CBB) R-250 organic dye from aqueous solutions, achieving a remarkable removal efficiency of 96.16 %. The morphology of the nanocomposite was characterized using SEM and FTIR, revealing particle sizes of less than 18 nm. Additionally, BET analysis was performed, indicating a high surface area that enhances adsorption capacity. The influential variables affecting dye removal, including solution pH, stirring time, adsorbent dosage, initial dye concentration, temperature and ionic strength, were optimized. The adsorption process was analysed using Langmuir, Freundlich, Temkin and Dubinin?Radushkevich isotherm models. The experimental results indicated that the process followed the Freundlich and Temkin isotherm models, suggesting the heterogeneous nature of the adsorbent surface. The kinetic conditions of adsorption were investigated using pseudo-first order and pseudo-second-order models, with results showing that the adsorption process of CBB followed the pseudo-second-order kinetic model, indicating the chemical adsorption of the dye onto the magnetic nanoparticles. The thermodynamic studies also revealed the spontaneous nature of the adsorption process, with a positive slope of the Van?t Hoff curve indicating an exothermic reaction. Due to the equilibrium time of 5 min in the adsorption mechanism, the synthesized magnetic nanocomposite demonstrated a high CBB dye removal rate, making it suitable for treating dye-containing solutions.