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

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

Analytical Performance of Polymer-Based Microfluidic Devices Fabricated By Computer Numerical Controlled Machining

A study comparing the electrophoretic separation performance attainable from microchips molded by masters fabricated using conventional CNC machining techniques with commercial microchips, wire imprinted microchips, and microchips from LIGA molding devices is presented. An electrophoresis-based detection system using fluorescence microscopy was used to determine the analytical utility of these microchips. The separation performance of CNC microchips was comparable to commercially available microchips as well as those fabricated from LIGA masters. The important feature of the CNC machined masters is that they have rapid design-to-device times using routinely available machining tools. This low-cost prototyping approach provides a new entry point for researchers interested in thermoplastic microchips and can accelerate the development of polymer-based lab-on-a-chip devices