Direct Transverse Relaxation Time Biosensing Strategy for Detecting Foodborne Pathogens through Enzyme-Mediated Sol–Gel Transition of Hydrogels

In this work, we develop a direct transverse relaxation time (T2) biosensing strategy and employ it for assaying foodborne pathogens relying on the alkaline phosphatase (ALP)-mediated sol–gel transition of hydrogels. ALP can catalyze the reaction to generate an acidic environment to transform the sol-state alginate solution to hydrogel, and this hydrogelation process can directly regulate the diffusion rate of water protons that results in a T2 change of water molecules. By means of enzyme-modulated sol–gel transition and antigen–antibody interactions, this T2 biosensor displays high sensitivity for detecting 50 CFU/mL S. enteritidis within 2 h. This biosensing strategy directly modulates the water molecules rather than magnetic probes in traditional methods, offering a straightforward, novel, and sensitive platform for pathogen detection.