A Lab Prototype for Rapid Electrochemical Detection of <i>Escherichia coli</i> in Water Using Modified Screen-Printed Electrodes

Recognizing the need for a hand-held device capable of quantitatively measuring the concentration of bacteria in water, this paper describes a label-free method for rapid detection of <i>Escherichia coli</i> (<i>E. coli</i>) in water via H₂O₂ decomposition using screen-printed electrodes (SPE) modified with nanostructured metal oxide layers. The study encompasses sensor preparation, bacteria culture, synthesis and characterization of nanostructures, and development of a readout circuitry for lab prototyping. During sensing measurements, the bacteria are first made to interact with H₂O₂ and subsequently, the H₂O₂ solution is exposed on the sensing surface. The electrochemical sensors are fabricated by modifying the working electrode of SPE with nanostructured metal oxide layers of MnO₂ and TiO₂ as these play a crucial role in the detection of <i>E. coli</i> in water. The sensing experiments of MnO₂-modified SPE show a significant response to bacteria with a sensitivity of 0.82 mV.mL/log CFU and a limit of detection (LOD) of 1.8 CFU/mL, while the TiO₂-modified SPE exhibits a linear response over a wide range of bacterial concentrations with a sensitivity of 1.12 mV·mL/log CFU and a limit of detection of 2.23 CFU/mL. Both sensors demonstrate a rapid response, stability, repeatability, and a recovery time of 70 ms. Additionally, selectivity with respect to other bacteria, wastewater components such as glucose, ammonium sulfate, and sodium carbonate, and testing with RO, DI, and tap water samples are conducted to evaluate the sensors' performance. A detailed sensing mechanism has been developed to comprehend the results, including chemical and biological reactions, metal oxide interfaces, morphology, and other surface studies of the sensing surface. A prototype comprising a sensor chip, an Arduino board, and other necessary circuit components is tested with various bacterial solutions. This enables its use for on-field rapid detection of bacteria in water using smaller volumes and a portable system.