An impedimetric aptasensor for Shigella dysenteriae using a gold nanoparticle-modified glassy carbon electrode

This work describes an aptasensor for the foodborne pathogen Shigella dysenteriae (S. dysenteriae). A glassy carbon electrode (GCE) was modified with gold nanoparticles (AuNPs) by electrodeposition. Then, thiolated aptamer for S. dysenteriae detection was self-assembled on the surface of the modified GCE, and any free residual AuNPs were blocked with 6-mercapto-1-hexanol. The size, morphology, and distribution of the AuNPs were characterized by field emission scanning electron microscopy. Detection of S. dysenteriae was performed measurement of the charge transfer resistance (R_ct) before and after addition of S. dysenteriae using hexacyanoferrate as an electrochemical probe. The interaction between the aptamer and outer-membrane proteins of S. dysenteriae lead to an increase in the R_ct of the sensor. The assay has a linear dynamic range that extends from 10¹ to 10⁶ CFU.mL⁻¹ and a limit of detection of 10⁰ CFU.mL⁻¹. It can differentiate between alive S. dysenteriae and other pathogens. Dead S. dysenteriae cells do not have any effect on selectivity. Unpasteurized and pasteurized skim milk and some water samples were spiked with S. dysenteriae and then successfully examined by this method. The results were validated by real-time PCR. The method is fast, low-cost, highly sensitive, and specific. Hence, it represents a valuable tool in food quality control. .