Conjugated Molecule Based Sensor for Microbial Detection in Water with E. coli as a Case Study and Elucidation of Interaction Mechanism

Water testing for microbial contamination is essential to ensure safe drinking water. In the present work, an organic nanocomposite based sensor is designed and fabricated to detect the presence of E. coli in water. The detection is carried out by measuring the change in two parameters of the organic nanocomposite film – resistance and impedance. The lower detection limit of E. coli cell counts up to 10 CFU mL−1 and 107 CFU mL−1 in 100 mL test solution is observed by impedance spectroscopy and resistance change respectively. A conjugated molecule with a specific pendant amine group was used as the receptor moiety that can interact and exhibit affinity to the functional groups like carboxyl groups present on the outer membrane of the cell wall of the E. coli. The binding of E. coli cells to conjugated molecule was characterized by chemical, physical and structural properties. The electrostatic interaction between positively charged amine groups on conjugated molecule and negatively charged E. coli is utilized for sensing. This interaction is also observed to be acting as p‐dopant to conjugated molecule which synergistically induces a change in electrical resistance in the composite. This work shows that the conjugated molecules designed with suitable moieties could be used for sensing microorganisms, when most sensors for detection of E. coli cells, use antibodies as detecting element.