Label-Free Detection of Waterborne Pathogens Using an All-Solid-State Laser-Induced Graphene Potentiometric Ion Flux Immunosensor

Waterborne pathogens are harmful microorganisms transmitted through water sources. Early and rapid pathogen detection is important for preventing illnesses and implementing stringent water safety measures to minimize the risk of contamination. This work introduces a miniaturized all-solid-state potentiometric ion flux immunosensor for the rapid and label-free detection of waterborne pathogens. A screen-printed silver/silver chloride electrode coated with a reference electrode membrane and polyurethane as an all-solid-state reference electrode was combined with a solid-state contact ion-selective electrode (ISE). An all-solid-state ISE was constructed on laser-induced graphene by coating it with a cationic marker and a carboxylated poly(vinyl chloride)-based membrane for immobilizing antibodies and controlling ion fluxes through the membrane. Proof-of-concept was achieved by detecting Escherichia coli and Salmonella enterica serovar Typhimurium using the assembled immunosensors within 10 min. The potentiometric response shift attributed to the blocking effect in the ion flux caused by pathogen-antibody interaction corresponded to pathogen concentration, indicating detection limits of 0.1 CFU/mL and working ranges of 0.1-10⁵ CFU/mL. Furthermore, the developed sensors revealed high selectivity and were directly applied in groundwater and tap water without any sample preparation, demonstrating high recovery percentages. The simple operation and elimination of sample preparation are key benefits to further usability of the developed immunosensors for efficient pathogen detection.