Miniature lab-made electrochemical biosensor: A promising sensing kit for rapid detection of E. coli in water, urine and milk

A novel, rapid production methodology for laboratory-made carbon electrodes (LCE) employing cost-effective and readily available materials has developed in the present work. The LCE presents superior electrochemical characteristics compared to commercially available screen-printed carbon electrodes (SPCE). Furthermore, this research has demonstrated the performance of readily accessible, highly sensitive, and portable biosensors for on-site detection of E. coli in aqueous samples. Silver nanoparticles (AgNPs) were successfully electrodeposited onto the LCE (Ag-LCE) using the electrochemical method at optimised parameters. The E. coli-specific aptamer was conjugated with AgNPs, and uncoated Ag-LCE surfaces were blocked with a BSA (BSA-Apt-Ag-LCE). The developed BSA-Apt-Ag-LCE biosensor was characterised and validated for the successful detection of E. coli in aqueous samples using cyclic voltammetry (CV). A linear correlation was obtained for sensor response in the 3.4 × 10¹ to 3.4 × 10⁶ CFU/ml bacterial concentration as ΔI<inf>pa</inf> = 5.71 log C + 2.91 with R² = 0.987. BSA-Apt-Ag-LCE biosensors have a limit of detection of 34 CFU/ml and a response time of 15 min, indicating their prompt and practical on-site identification capabilities. The proficient detection of E. coli in diverse aqueous samples, substantiated by its consistent reproducibility as indicated by the relative standard deviation (RSD) value of a maximum of 1.71 %, is a compelling validation of the biosensor's efficacy and reliability. The proposed biosensor exhibited selectivity towards E. coli and was found stable even after being stored at 4 °C for four weeks.