金属酸化物/炭素ナノ複合体および金属有機構造体の高感度電気化学センサへの応用

概要

Electrochemical sensor plays an important role in the research of analytical chemistry because of its sensitivity, rapidity, low cost, portable detection device, low energy consumption and easy miniaturization and integration. It has been applied in many fields, such as biomedicine, environmental protection, electrochemical catalysis, and so on. Recently, the functionalization of metal-oxides and MOFs have been attracting wide attention based on their excellent performance and the construction of electrochemical sensor is one of their most promising applications because their intervention provides a broad space for the development of electrochemical sensors. Therefore, the application of the functional metal-oxides and MOFs provides a new strategy for the study of biomolecules and chemical molecules in the electrochemical sensing field. The thesis consists of 4 chapters and the abstract of each chapter is shown as follows:

Chapter 1: The brief introduction of electrochemistry; the functionalization of metal-oxides and MOFs are described. Moreover, some questions of the previous studies are pointed out and the significance and purpose of this study were stressed.

Chapter 2: The functionalization of metal oxide-carbon nanocomposites and their application in electrochemical sensors.
2-1 Porous nanododecahedron of Co3O4/C nanocomposites were synthesized and was used for fabricating a highly sensitive and low oxide potential nitrite ion (NO2−) sensor. The structure and morphology characterization showed that ZIF-67 behaves as an ideal sacrificial template to produce Co3O4/C nanocomposites with regular shape. Electrochemical analysis showed that the excellent electrocatalysis performance toward the oxidation of NO2− based on the synergy of Co3O4 and carbon in the nanocomposite. The nanocomposite acted as an electrochemical sensing material for determination of NO2− in the real samples.

2-2 A thin nanosheet structure of ZrO2/C nanocomposites was prepared used UiO-67 with a flat cuboid structure as precursor. The peculiar and fluffy structures endowed materials with high surface area that tremendously improved the adsorption capacity of electrode materials for heavy metal ions. Thus, ZrO2/C nanocomposites was used as an electrode material to simultaneous detection of Pb(II) and Cd(II) in 0.1 M HAc-NaAc buffer by differential pulse anodic stripping voltammetry (DPASV). Under the optimal conditions, the results showed that prepared sensor possessed the high sensitivity, good stability and low interference of the detection for two metal ions, and the limit detections for Pb(II) and Cd(II) of 0.007 μM and 0.019 μM were estimated, respectively. Furthermore, it was also successfully applied for the detection of trace Pb(II) and Cd(II) in real water samples. 2-3 An inorganic-organic hybrid material consisting SnO2-C yolk-shell nanospheres and poly-Tyrosine (pTyr) has been developed for DNA biosensor fabrication. Electrochemical experiments showed that the existence of SnO2-C in the hybrid matrix remarkably enhanced the effective surface area, and the pTyr provided not only abundant carboxyl groups for covalent bonding with pDNA but also 4'-hydroxyl group giving the hydrogen bonding with the base groups of pDNA. When tDNA was hybridized with the probe DNA, the “signal-off” response in EIS measurement was obtained. The reason is likely related to the change of the state and environment of the biosensor surface before and after hybridization reaction. An ultralow detection limit of 0.53 aM for CaMV35s promoter gene is achieved. Meanwhile, it potentially becomes a convenient tool of PCR-free TG sequences analysis for medical, pabular, and environmental purposes.

Chapter 3: The functionalization of metal-organic frameworks (MOFs) and their application in electrochemical sensors.
3-1 A flexible metal-organic framework (MOF) of Cu2(trans-1,4-cyclohexanedicarboxylic acid)2 (Cu2(CHDC)2) has been synthesized by a facile hydrothermal method. The characterization experiments show that the Cu2(CHDC)2 presents unique flower-like shape, large surface area and high electroactivity. Then, gold nanoparticles (AuNPs)/Cu2(CHDC)2 modified electrode was prepared and was utilized as an electroactive matrix for thrombin aptamer immobilization. Upon the binding of the electrode-confined aptamer with the thrombin, the electrochemical signal of the Cu2(CHDC)2 decreased obviously due to the change of the microenvironment of the sensing interface. Thus, a label-free electrochemical sensing strategy for thrombin was realized. The aptasensor displayed an excellent performance with wide linear range, ultralow detection limit of 0.01 fM (S/N=3) and favorable specificity. Also, the aptasensor was applied for determination of thrombin in the human serum samples.

3-2 A rational, sensitive and reusable electrochemical aptasensing strategy for Ochratoxin A (OTA) was proposed using in-situ coordination-assembled UiO-66 as signal amplification platform in the design, the OTA aptamer was pre-hybridized with supporting strands that immobilized on the gold electrode surface. Then, the classic Zr-MOF of UiO-66 was in-situ immobilized on the terminal of OTA aptamer through coordination between Zr4+ and 5'-PO43- modified on OTA aptamer.

Furthermore, the signal probe with electroactive tag of methylene blue was in-situ assembled on UiO-66 by the Zr-O-P bond. Because of large surface area and rich active sites owing to Zr4+, the comparative assay showed that the UiO-66 greatly enhanced the analytical performance of the aptasensor. A wide detection range from 0.1 fM to 2.0 μM and an ultralow detection limit of 0.1 fM (S/N = 3) for target OTA were achieved. In addition, because the aptasensor was designed on the basis of the auxiliary strand-based competitive binding strategy, 11 times reusability of the aptasensor could be attained in accompany with the detection process. The aptasensor could also be applied for detection of OTA in the red wine sample, demonstrating a promising prospect of the biosensor for food safety monitoring.

Chapter 4: Conclusions and scope of these studies were described.