Low-cost gold-leaf electrode as a platform for Escherichia coli immuno-detection

Gold electrodes are one of most prevalent substrates in electrochemical biosensors because they can be easily and highly efficiently functionalized with thiolated biomolecules. However, conventional methods to fabricate gold electrodes are costly, time consuming and require onerous equipment. Here, an affordable method for rapid fabrication of an electrochemical immune-sensor for Escherichia coli detection is presented. The gold electrode was generated using 24-karat gold leaves and low-cost polyvinyl chloride adhesive sheets covered with an insulating PTFE layer. The gold-leaf electrode (GLE) was patterned using laser ablation and characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electronic microscopy, contact angle and 3D profiling. The GLEs were modified by a self-assembled mercaptopropionic monolayer, followed by surface activation to allow binding of the specific anti-E. coli antibody via carbodiimide linking. The biosensor showed a detection limit of 2 CFU/ml and a linear dynamic range of 10 - 107 CFU/ml for E. coli cells. No false positive signals were obtained from control bacteria. The obtained results demonstrated suitability of GLE for use in biosensors with high reliability and reproducibility. It is foreseeable that our work will inspire design of point-of-need biosensors broadly applicable in low-resource settings.