Development of Aptamer-Based Electrochemical Biosensor Using Ag-Modified Screen-Printed Carbon Electrode for the detection of E. coli in water sample

Abstract

E. coli serves as an indicator organism for assessing fecal contamination and the potential presence of waterborne pathogens. However, the traditional methods employed for detection of bacteria are time-consuming and need pre-enrichment, DNA isolation, amplification, and purification. Moreover, these methods demand the use of complex instruments, laboratories, and skilled professionals. The present work has demonstrated the development of easy, rapid, sensitive, and portable biosensor for the onsite detection of E. coli in water samples. The screen-printed carbon electrodes (SPCE) were modified by electrodeposition of Ag particles onto the working electrode using 3 mM AgNO3 in 0.1 M KNO3 solution. The distribution of the particles over the electrode surface and the particle size were analyzed by scanning electron microscopy (SEM). A thiol-modified DNA aptamer specific to the E. coli ATCC 8739 strain was immobilized onto the electrode surface through thiol-Ag covalent binding. The aptamer functionalized SPCE was characterized using cyclic voltammetry (CV). The functionality of the biosensor was determined by differential pulse voltammetry (DPV). A proportional decrease in the current signals was observed with increasing E. coli concentration. The linearity was obtained from 53 CFU/ml to 1.06 × 106 CFU/ml. The regression line equation was obtained as ΔI = 5.8980C + 5.7113 with R2 = 0.97. A relative standard deviation (RSD) was calculated as 3.46 % (n = 3), which showed good reproducibility. The developed biosensor demonstrated minimum detection limit of 53 CFU /ml E. coli in a response time of 15 minutes