An ultrasensitive bacteria biosensor using “multilayer cake” silver microelectrode based on local high electric field effect

A signal response mechanism of local high electric field effects was designed to detect bacteria using a chemically modified “multilayer cake” micro-nanostructured pillar electrode. Since the silver electrode has a strong specific electrochemical signal response to chloride ions, we choose silver as the electrode material. The microelectrode was prepared by a one-step localized electrochemical deposition method without the use of mold. Then the electrode was successively functionalized with chitosan, catechol, and aptamer. Many nano- and micro-scale protrusion tips on the electrode surface generated a local high electric field and drove the leakage of intracellular chloride ions when bacteria were captured by APT; thus, a reduced signal of the silver electrode related to chloride ions was recorded. A pseudocapacitor structure composed of chitosan, catechol, Ru3+, and Fc was constructed on an electrode surface to further amplify the signal. The electrochemical sensor based on this electrode showed excellent performance for template bacteria Staphylococcus aureus detection in terms of the detection limit (1 CFU mL−1), linear response range (1–105 CFU mL−1), and specificity. This work provides another way to design an electrochemical biosensor using the nanoeffect of the electrode rather than the conventional current response based on the electrical properties of the bacterial surface.