Liquid crystal immunosensors for the selective detection of Escherichia coli with a fast analysis tool

• Sandro Oliveira, Simone Soares, Barbara goncalves, Andreia rodrigues, Amadeu Soares Soares, rita sobral, Nuno Santos, Jan Nedoma, Pedro Almeida, and Carlos Marques
• received 03/26/2024; accepted 04/27/2024; posted 04/29/2024; Doc. ID 524660
• Abstract: The consumption of contaminated food can cause very serious illnesses, but traditional methods of Escherichia coli detection are still associated with long waiting times and high costs given the need to transport samples to specialized laboratories. There is a need to develop new technologies that allow cheap, fast, and direct monitoring at the site of interest. Thus, in this work, we developed optical immunosensors for the specific detection of E. coli, based on liquid crystal technology, whose molecules can align in different manners depending on the boundary conditions (such as substrates) as well as the environment that they experience. Each glass substrate was functionalized with anti-E. coli antibody using cysteamine as an intermediate, and a vertical alignment was imposed on the liquid crystal molecules by using DMOAP during functionalization. The presence of bacteria disrupts the alignment of the liquid crystal molecules, changing the intensity of light emerging between cross polarizers, measured using a polarized optical microscope and a monochromator. It was possible to detect E. coli in suspensions in the concentration range from 2.8 cells/mL to 2.8×109 cells/mL. Selectivity was also evaluated, and the sensors were used to analyze contaminated water samples. A prototype was also developed to allow faster, in-situ and easier analysis avoiding bulky instruments.