Liquid Crystal-Based Immunosensor for the Optical Detection of Escherichia Coli at Low Concentration Levels

The fast and specific detection of the commensal and pathogenic bacteria Escherichia coli (E. coli) is an essential challenge in the aquaculture industry. Herein, we developed and validated a liquid crystal-based optical biosensor that exhibited the capacity to detect whole-cell E. coli with a detection limit of 2.8 CFUs/mL. The inner surfaces of the device were treated so that the molecules of nematic liquid crystal 4-Cyano-4'-pentylbiphenyl were perfectly aligned along a direction normal to the confinement surfaces. Anti-E. coli-specific antibodies were immobilized on the inner surfaces of the device to function as biorecognition molecules. The size of the bacterial cells is over one thousand times higher than the size of the liquid crystal molecules, so when in contact, they efficiently distort the mean orientation of the liquid crystal molecules, which is the principle behind the detection method. Our whole-cell biosensor presents several advantages; it is a low-cost device for simple optical reading and interpretation that relies on portable technology. This immunosensor presents a faster detection time and a lower limit of detection (LOD) than most LC-based sensors described to detect bacteria. This study is an important contribution to a fast diagnosis, which allows to address a specific threat, with immediate application to the aquaculture field, an increasingly important industry.