Novel Signal Enhanced Liquid Crystal Biosensors For Biomolecular Assay

As a novel method, the liquid crystal biosensor is of great potential for providing simple, fast, highly sensitive and label-free bioassays. With the higher requirements of modern biological analysis, developing new liquid crystal biosensing methods with high sensitivity, high selectivity has become a new challenge in recent years. So, it is very important to develop signal enhancement liquid crystal biosensors. In the paper, we mainly developed several signal enhanced liquid crystal biological sensing methods by taking use of nucleic amplification reaction.1. A novel nucleic acid liquid crystal biosensor is developed for the p53mutant gene, which is based on the branched nucleic acid hybridization reaction and the orientational transition of liquid crystal. Herein, a specific target DNA sequence is used as an initiator, three different hairpin probes as dendritic monomers, and the branched-like DNA with controllable molecular size and weight can be formed by changing the concentrations of the monomers and the reaction time under mild conditions. And then branched-like DNA is hybridized with the capture DNA sequences on the glass substrate. Making use of unique birefringent properties of liquid crystal molecules, the sensor can get an enhanced polarization response signal, and achieve the rapid and specific detection low to1nmol/L mutant DNA strand..2. Using thrombin aptamer as the "sensing element" and introducing biotin-streptavidin binding of gold nanoparticles as the "signal amplifying elements" we construct a novel signal-enhanced liquid crystal biosensor for the detection of thrombin. The thrombin aptamer is designed to be a hairpin probe, which is labeled by an amino group and a biotin group at its two ends, espectively. The detecting principle is based on the conformational change of thrombin aptamer after it specifically binds to a target protein. Streptavidin-labeled gold nanoparticles are captured by the biotin-streptavidin system, and then aptamers-thrombin-gold nanoparticles sandwich complexes can be formed on the sensor interface. The sandwich complexes can effectively disrupt the orderly arrangement of the liquid crystal molecules, and the optical appearance of the5CB then changes from uniformly black to bright. The results show that it has observable optical responses of LCs to thrombin when its concentration is low to5pmol/L. Moreover, there is no obvious optical signal and the optical appearance of5CB still remaines black when some other proteins present in the detection system. These results well indicate that the proposed method have a high sensitivity and selectivity, which is of great significance to further expand the range of applications of the liquid crystal biosensors.3. A label-free liquid crystal biosensing method for the detection of Hg2+in aqueous solution has been developed. The method is based on the specific and strong binding of Hg2+by two DNA thymine bases (T-Hg2+-T). The adsorption of ionic surfactant to the LC-aqueous interface can result in homeotropic LC alignment due to the anchoring interaction of the tails of surfactant. The Hg2+biosensor system is composed of two label-free DNA probes with ten T-T mismatches, which can specificly form stable DNA duplexes by T-Hg2+-T in the presence of Hg2+. With the absence of Hg2+at the aqueous-liquid crystal interface, the liquid crystal will assume an orientation that is locally homeotropic to the interface after contacting with SDS. The subsequent adsorption of the two single-stranded DNA probes to the SDS-laden interface changes the interfacial structure, resulting in a reorientation of the LC from homeotropic to planar state. Exposure of the ssDNA/SDS interfacial complex to Hg2+induces a second change in the interfacial structure and further induces homeotropic LC alignment. The bright-to-dark shift in the optical signal do not take place in the presence of other metal ions even at high concentrations. Considering its easy, label-free and selectivity, the experimental system is expected to provide a new platform for the detection of Hg2+analysis.