Carbohydrate-Based Label-Free Detection of <i>Escherichia coli</i> ORN 178 Using Electrochemical Impedance Spectroscopy

Abstract

A label-free biosensor for <i>Escherichia coli</i> (<i>E. coli</i>) ORN 178 based on faradaic electrochemical impedance spectroscopy (EIS) was developed. α-Mannoside or β-galactoside was immobilized on a gold disk electrode using a self-assembled monolayer (SAM) via a spacer terminated in a thiol functionality. Impedance measurements (Nyquist plot) showed shifts due to the binding of <i>E. coli</i> ORN 178, which is specific for α-mannoside. No significant change in impedance was observed for <i>E. coli</i> ORN 208, which does not bind to α-mannoside. With increasing concentrations of <i>E. coli</i> ORN 178, electron-transfer resistance (<i>R</i>_et) increases before the sensor is saturated. After the Nyquist plot of <i>E. coli</i>/mixed SAM/gold electrode was modeled, a linear relationship between normalized <i>R</i>_et and the logarithmic value of <i>E. coli</i> concentrations was found in a range of bacterial concentration from 10² to 10³ CFU/mL. The combination of robust carbohydrate ligands with EIS provides a label-free, sensitive, specific, user-friendly, robust, and portable biosensing system that could potentially be used in a point-of-care or continuous environmental monitoring setting