Investigation Of Functional Nucleic Acids In Photochemical Biosensor

Metal ions, proteins and nucleic acids are always crucial target analytes as they are closely related to the production and activities of human beings. Trace heavy metals in the environment could be enriched through the food chains. Heavy metals could be absorbed by people through drinking or eating heavy-metals-polluted water or foods. When the concentrations of heavy metals exceed a certain limitation in the body, they may engender various kinds of diseases. Moreover, nucleotides are basic genetic substances for organisms. The base mutations in them may bring numerous genetic diseases. Additionally, proteins are material basis of life activity metabolism. The amounts of certain proteins have been important biomarkers in clinic diagnose. Thus, constructing simple and rapid methods for metal ions, proteins and nucleotides detection is significant in biological fields. The investigation of photochemical biosensors holds great potential as they are endowed with numerous advantages such as low detection limit, rapid analysis, real-time and noninvasive analysis and so on. In this paper, we have developed several detection methods for metal ions, proteins and specific gene sequences based on optical methods as follows:(1) A label free sensor for lead ions (â…¡) detection has been designed firstly combining Pb2+-dependent DNAzyme with quantitative polymerase chain reaction (QPCR). Specifically, a substrate strand was designed to have two primer-hybridization sequences at either terminus. The presence of Pb2+ catalyzed the cleavage of the substrate strands. This resulted in a concentration decrease of the substrate strand, which could be detected by quantitative polymerase chain reaction (QPCR). The results revealed that our approach exhibited a good dynamic response toward Pb2+ range from 10 nM to 5μM, with a detection limit of 1 nM. Furthermore, our sensor has a good selectivity towards other divalent ions that commonly coexisted with Pb2+.(2) A novel homogeneous fluorescence protection assay has been proposed. Based on our principle, we are able to detect IgE rapidly and sensitively. The binding of IgE with its aptamer labeled with fluorescein isothiocyanate (FITC) hampered the binding of anti-fluorescein isothiocyanate (anti-FITC), which reserves the fluorescence emission of FITC. Through detecting the fluorescent intensity of FITC, we could detect IgE quantitatively. Our results demonstrated that our sensor has a favorable linear relationship toward IgE range from 1 nM to 40 nM, with a detection limit of 0.1 nM. Besides, our sensor has an excellent selectivity toward other proteins in human serum.(3) Taking advantage of the fluorescence quenching ability of single wall carbon nanotubes (SWCNT), a biosensor for specific DNA sequence detection has been constructed. The single-stranded DNA labeled with carboxyfluorescein (FAM) has been displaced from the surface of SWCNT through hybridization with its target strand. Through detecting the fluorescence intensity of the solution, we could detect specific target sequence as the fluorescence of FAM is restored after its dissociation from SWCNT. With this principle, we have successfully detected a specific sequence fromβ-thalassemia gene with a single-base mutation in-28 site (Aâ†'G). It was proved our sensor could discriminate single nucleotide polymorphism.