Label-Free\nDetection of Waterborne Pathogens Using\nan All-Solid-State Laser-Induced Graphene Potentiometric Ion Flux\nImmunosensor

Waterborne pathogens are harmful microorganisms transmitted\nthrough\nwater sources. Early and rapid pathogen detection is important for\npreventing illnesses and implementing stringent water safety measures\nto minimize the risk of contamination. This work introduces a miniaturized\nall-solid-state potentiometric ion flux immunosensor for the rapid\nand label-free detection of waterborne pathogens. A screen-printed\nsilver/silver chloride electrode coated with a reference electrode\nmembrane and polyurethane as an all-solid-state reference electrode\nwas combined with a solid-state contact ion-selective electrode (ISE).\nAn all-solid-state ISE was constructed on laser-induced graphene by\ncoating it with a cationic marker and a carboxylated poly(vinyl chloride)-based\nmembrane for immobilizing antibodies and controlling ion fluxes through\nthe membrane. Proof-of-concept was achieved by detecting Escherichia coli and Salmonella enterica serovar Typhimurium using the assembled immunosensors within 10\nmin. The potentiometric response shift attributed to the blocking\neffect in the ion flux caused by pathogen–antibody interaction\ncorresponded to pathogen concentration, indicating detection limits\nof 0.1 CFU/mL and working ranges of 0.1–10<sup>5</sup> CFU/mL.\nFurthermore, the developed sensors revealed high selectivity and were\ndirectly applied in groundwater and tap water without any sample preparation,\ndemonstrating high recovery percentages. The simple operation and\nelimination of sample preparation are key benefits to further usability\nof the developed immunosensors for efficient pathogen detection.