The principles of LC-based biosensors is based  on the optical, anchoring, and birefringent properties of the LC material. The alignment of LC molecules can be changed by the introduction of the binding event of ligands and receptors at the biosensor surfaces. The resulting shifts can then be addressed by optical methods, and the changes in the original alignment are correlated with either the identity of the target and its concentration.

Hong Yu is vey right. I used to work in the R&D of Crystal Diagnostics, Ltd. which manufactures liquid crystal biosensors. You can take a look at their attached patent to fully understand how bacteria can be sensed using liquid crystals.

Muhammad Salili, Thanks for showing me your patent.    I mainly do some researchs on quartz crystal resonator related sensor. Also interested in the liquid crystal biosensors.