Low-Dimensional Nanomaterials Based Nucleic Acid Sensing System For Small Biomolecules And Heavy Metal Ions Detection

The physical and chemical properties of nanomaterials is very unique, contain small size effect, surface effect, quantum size effect and macroscopic quantum tunnel effect. The thesis is concentrated on the investigation of nanomaterials applied in aptamer sensor to detect Hg2+ and adenosine. Our main research focuse in the three aspects as follows:In Chapter 2, a polythymine oligonucleotide based homogeneous assay using nanoparticles (AuNPs) and SYBR Green 1 (SG) is unveiled for the selective and sensitive detection of Hg2+ in aqueous solution. The fluorescence of SG is weak in the presence of randomly coiled polythymine oligonucleotide. After polythymine oligonucleotide interacts specifically with Hg2+ through T-Hg2+-T bonding, its conformation changes to form a folded structure that preferably binds to SG. Hence the fluorescence of a mixture of polythymine oligonucleotide and SG increases with the introduction of Hg2+. The quenching capability of AuNPs makes low background and high selectivity of the assay. The proposed senor exhibits a high selectivity toward Hg2+ over other metal ions. The linear range of proposed sensor for quantitative determination is from 150 nmol·L-1 to 1.0 μmol·L-1 and a detection limit of 109 nm. The practicality of this probe is demonstrated for the rapid determination of Hg2+ in real samples. This approach offers several advantages, including rapidity, simplicity, and cost-effectivity.In Chapter 3, single-walled carbon nanotubes (SWNTs) is applied in a fluorescence biosensor for mercury ion analysis. The conformation of the T-rich single-strand aptamer changes to a double-strand owning to the specific binding between Hg2+ and thymine-thymine (T-T) base pair. The SYBR Green 1(SG) inserts into the double strand aptamer with a strong fluorescence signal. The SWNTs produces a good signal-to-background ratio. The linear range of proposed sensor for quantitative determination is from 150 nmol·L-1 to 3.0 μmol·L-1. and a detection limit of 139 nm.This sensor provides a simple, effective, and universal platform for mercury ion detection.In Chapter 4, a novel electrochemical aptamer sensor has been designed for detection of adenosine in this study. In the presence of adenosine, complementary oligonucleotide pairs has been hybridizated, The RCA was performed with pHi 29 DNA polymerase to produce a long single strand, which was complementary to the circle template probe. Large amounts of gold nanoparticles labeled oligonucleotide probes were hybridized with the product of RCA. As a result, the impedance response of the sensing interface for recognition of adenosine was enhanced by the RCA strategy. The proposed sensor possessed nice selectivity and reproducibility, and was applied to determination of adenosine samples with a linear range between 5.0 μM and 100 μM and a detection limit of 5.0 μM.