Studies On The Liquid Crystal Biosensors For Small Molecules

Small molecules and proteins in the life activity of human are indispensablematerials, their detections are also of great importance. However, the small moleculesusually have small molecular weight and size. Due to those limitations, small moleculedetection is more difficult than protein detection.Liquid crystal (LC) is a kind of special material which can exhibit the mobility ofliquids and the anisotropy of solid crystals. Based on the special properties of the LC,Abbott and co-workers proposed a new concept named LC biosensor by using LCs assensing elements in the detection of biomolecules. The LC biosensor is simple, robust,and inexpensive, and it is easy to miniaturization and array.Aptamers can specifically recognize small moleculars，and it usually accompanyby a notable structural change aptamers. Such a structural change is able to induce ahomeotropic-to-tiled transition of the LC molecules surrounding them, and furtherproduce the optical signal change of optical images under the crossed polarized light.In the thesis, we developed several small molecular LC biosensors based on theprinciple. The detailed methods are as follows:(1)We presented a novel LC biosensor for the detection of adenosine triphosphate(ATP) based on the two split aptamer chips specifically recognize and binding withATP. The TEA/DMOAP mixed self-assembled monolayer (SAM) which can induceLC molecules homeotropic alignment modified on the glass surface and the5’-amino-modified oligonucleotide probe which contain a part of ATP aptameroligonucleotide immobilized on the glass surface via covalent bind. In the presence ofATP, those two split aptamer chips will be special hybridization with each other andthe ternary complex is formed. The aptamer structure change which can disrupt theorientational arrangement of LCs, and case the optical signal image change. We alsoinvestigated the experimental condition, specificity, and detection performance. Theresult showed that the proposed method can detect ATP concentration as low as10nMand it is a sensitive and simple sensor to realize the detection of ATP.(2)We constructed an ultrasensitive Hg2+LC sensor based on the specificalrecognization of Hg2+by two DNA thymine bases (T-Hg2+-T). There were threeessential elements: a thymine-rich (T-rich) hairpin oligonucleotide probe, a T-richsingle-stranded oligonucleotide probe, and a5’-amino-modified oligonucleotide probe. The5’-amino-modified oligonucleotide probe, as capture probe, was first immobilizedon the glass surface modified with the TEA/DMOAP mixed self-assembled monolayer(SAM). In the presence of Hg2+，the T-rich single-stranded oligonucleotide and theT-rich hairpin oligonucleotide probe probe then hybridized via the special T-Hg2+-Tinteraction, and maked the hairpin loop open. The latter further hybridized with thecapture probe immobilized on the SAM. The change of molecular space conformationand size before and after hybridization led to the optical signal change of LC sensor.The proposed method can detect Hg2+concentration as low as0.1nM, exhibiting highsensitivity.(3) We proposed a kind of ATP liquid crystal biosensor based on conformationtransition principle. A Hairpin oligonucleotide probe and A single-strandedoligonucleotide probe were designed for the recognization of ATP. The single-strandedoligonucleotide probe was first immobilized on the glass slide modified theTEA/DMOAP mixed SAM. The hairpin oligonucleotide probe and the single-strandedoligonucleotide probe possess different parts of the recognition sequences of ATPaptamer which can specifically recognize of ATP. In the presence of ATP, these twoprobes can combined together with ATP and formed a ternary complex, leading thehairpin probe to be opened and immobilized on the SAM. The introduction of the ATPternary complex after hybridization can cause the optical signal change from black tobirefringent texture. This LC sensing method has good sensitivity and selectivity sincethe hairpin oligonucleotide probe conformation transition.