| Liquid crystal (LC) exhibits a special state of matter intermediate between a true crystal and an isotropic liquid known as liquid-crystal phases in a certain temperature range, which has been widely used in display technology because of their special physicochemical and optoelectronic properties. LC not only possesses the birefringence of crystals, but also has the mobility of liquid. The detection principles of liquid crystal biosensor rely on liquid crystal birefringence of polarized light. The target molecular which is introduced to sensing substrate interface can result in changes liquid crystal orientation alignment and different optical response signals can be observed under polarized-light microscope, thus realizing the target detection. The LC-based sensor has the advantages of simple operation, rapid response and does not require sophisticated equipment, more importantly, is easy to realize miniaturization and array, and so on. Combining those characteristics of the LC-based sensor and the specific recognition of DNAzymes to metal ion cofactors several novel optical sensors have been investigated for mental ion in this paper and described as follows:In chapter2:A novel liquid crystal biosensor has been developed for the detection of Pb2+with high sensitivity and high selectivity. In this method, a chemically functionalized surface on a cleaned plain glass slide was first obtained by self-assembling a triethoxsilylbutyraldehyde (TEA)/N, N-dimethyl-N-octadecyl-3-aminopropyl trimethoxysilyl chloride (DMOAP) film, which cannot only provide plentiful amino groups for coupling with DNA probes and proteins but also orientate LC alignment and provide a uniform dark backdrop. Then, the capture DNA probe immobilization was carried out by covalently binding the capture probe to the mixed TEA/DMOAP film surface, followed by hybridization of the target DNA fragments releasing from DNAzyme cleavage reaction in the present of Pb2+to form DNA duplexes. The bound DNA duplexes on the substrate surface will bring about a greatly change in the topographical features of LC-interface and further induce a homeotropic-to-tiled transition of the LC molecules surrounding them, resulting in an obvious change of the optical appearance of LC biosensors from a dark background to a birefringent texture. This biosensor not only permits the label-free and low-cost detection of Pb2+but also shows a high sensitivity and good selectivity, with the detection limit of10nM.In chapter3:A label-free liquid crystal biosensor was developed based on uranyl-dependent DNAzyme. In this study, the capture DNA probe was immobilized on the TEA/DMOAP-treated substrate surface through covalent bind working. In the presence of UO22+, the substrate strand was cleaved at the rA site by the enzyme strand and the subsequent release of the cleaved product were complementary to the capture probe on the LC sensing substrate to form duplex-like complexes through the Watson-Crick base pairing, which will sensitively distort the orientation of LC, leading to an enhanced optical signal and thus the sensitive LC sensing detection of UO22+was achieve. The results suggest that the above mentioned LC-biosensor is sensitive to the UO22+and the detection limit of the sensor is as low as25nM.In chapter4:A label-free fluorescence was also developed based on the reaction of cleave fraction uranyl-specific DNAzyme. In the presence of UO22+, using SYBR Green I (SG I) was used as the output to detect UO22+, which can produce strong fluorescence after embedding itself into double strand DNA but provide weak fluorescence after binging to single strand DNA. The system exhibits a dynamic response range for UO22+from0.1to1μM with a detection limit of100nM. |
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