A Simple Liquid Crystal-based Aptasensor Using a Hairpin-shaped Aptamer for the Bare-Eye Detection of Carcinoembryonic Antigen

Sensitive detection of carcinoembryonic antigen (CEA) is highly important in clinical diagnosis because CEA is an effective tumor marker associated with gastric, lung, rectal, and breast cancers. Thus, the development of an accurate, simple, and efficient method for the detection of CEA remains a long-term clinical goal. In this study, a liquid crystal-based aptasensor was constructed for the labelfree and sensitive detection of CEA. The aptamer, as a molecule identification element, was immobilized onto (3-aminopropyl)triethoxysilane (APTES)- and dimethyloctadecyl[3-(trimethoxysilyl) propyl]ammonium chloride (DMOAP)-modified surface slides through glutaraldehyde (GA); this aptamer can specifically bind to CEA. In the presence of CEA molecules, the loop-stem structure of the aptamers coated onto the surface of the slides opens, and the aptamer then combines with CEA, leading to the formation of aptamer-CEA complexes, which causes the orientation of the liquid crystal molecules (LCs) to transition from a homeotropic to a random alignment. This transition can easily be observed using polarized light microscopy, based on the change of dark optical images into bright ones. The aptasensor system is quite sensitive, as the detection limit is as low as 0.12 pg/ml, with a linear equation of Grayscale=20.318logC(CEA)+26.329 (R-2=0.9925), for a CEA concentration range of 0.05 pg/ml to 50 ng/ml. Bovine serum albumin (BSA) and human serum albumin (HSA) were also tested in this experiment, indicating that this sensor can selectively distinguish between CEA and other interfering compounds with similar protein structures. Moreover, these results were further confirmed by atomic force microscopy (AFM) and ellipsometry.