Impedimetric detection of Escherichia coli with bacteriophage immobilized polyaniline-chitosan modified thread based biosensor for healthcare and water quality monitoring

Escherichia coli (E. coli), is a gram negative, rod shaped, facultative anaerobic bacterium that serves as a model microbe in biological research, antibiotic resistance studies and environmental monitoring. Pathogenic strains of E. coli cause major food and water-borne infections, making their rapid and accurate detection in water and clinical samples critical for good health and well-being of the public. This study presents a disposable cellulosic thread based impedimetric sensor for the specific detection of E. coli B40 as a model strain, in samples with low to high organic loads. The study was conducted using T4 bacteriophage as the biorecognition element on polyaniline and chitosan functionalized cellulosic thread substrates. Electrostatically immobilized phages enabled specific recognition of E. coli cells, followed by bacterial capture and lysis. This was reflected by an increased solution resistance and subsequent decrease, studied using electrochemical impedance spectroscopy. Other parameters including double layer capacitanceand electroactive surface area, were also evaluated for each stepwise modification. The immobilization of T4 phage and bacterial binding was confirmed using scanning electron microscopy and culture assays. The sensor could detect at a range of 103-106 CFU/mL, with a limit of detection of 103 CFU/mL in phosphate buffer saline and drinking water, and 104 CFU/mL in cerebrospinal fluid samples. Furthermore, the specificity of the sensor was validated against other non-host bacteria (E. coli DH5 Alpha, Staphylococcous aureus and Pseudomonas aeruginosa) and non-ionic interferents. This highlights its potential for the selective detection of E. coli B40 in clinical and environmental monitoring applications.