Magnetosome-anti-Salmonella antibody complex based biosensor for the detection of Salmonella typhimurium

Epidemic Salmonellosis contracted through the consumption of contaminated food substances is a global concern. Thus, simple and effective diagnostic methods are needed. Magnetosome-based biosensors are gaining attention because of their promising features. Here, we developed a biosensor employing a magnetosome-anti-Salmonella antibody complex to detect lipopolysaccharide (somatic "O" antigen) and Salmonella typhimurium in real samples. Magnetosome was extracted from Magnetospirillum sp. RJS1 and characterized by microscopy. The magnetosome samples (1 and 2 mg/mL) were directly conjugated to anti-Salmonella antibody (0.8-200 μg/mL) and confirmed by spectroscopy and zeta potential. The concentrations of magnetosome, antibody and lipopolysaccharide were optimized by ELISA. The 2 mg/mL-0.8 μg/mL magnetosome-antibody complex was optimal for detecting lipopolysaccharide (0.001 μg/mL). Our assay is a cost-effective (60%) and sensitive (50%) method in detection of lipopolysaccharide. The optimized magnetosome-antibody complex was applied to an electrode surface and stabilized using an external magnetic field. Increased resistance confirmed the detection of lipopolysaccharide (at 0.001-0.1 μg/mL) using impedance spectroscopy. Significantly, the R² value was 0.960. Then, the developed prototype biosensor was applied to food and water samples. ELISA confirmed the presence of lipopolysaccharide in homogenized infected samples and cross reactivity assays confirmed the specificity of the biosensor. Further, the biosensor showed low detection limit (10¹ CFU/mL) in water and milk sample demonstrating its sensitivity. Regression coefficient of 0.974 in water and 0.982 in milk was obtained. The magnetosome-antibody complex captured 90% of the S. typhimurium in real samples which was also confirmed in FE-SEM. Thus, the developed biosensor is selective, specific, rapid and sensitive for detection of S. typhimurium.