Synthesis of CuxO and MnOx nanomaterials for nanozyme and supercapacitor applications

• Main Authors: Wu, Chien-Wei, 吳建緯
• Other Authors: Huang, Chih-Ching
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/16534421042767595559

碩士 === 國立臺灣海洋大學 === 生命科學暨生物科技學系 === 103 === The first part, We synthesized DNA-capped copper nanoparticles (Cu NPs) using simple ascorbate-mediated reduction of Cu(II) ions in TBA29-Tn templates comprising of a 29-mer thrombin-binding aptamer (TBA29) with a poly(dT) (Tn; n = 6−30) motif in both 3′ and 5′ termini. High affinity between thymine and copper resulted in greater growth of Cu NPs along the poly(dT) scaffold. In this method, the DNA acts as the template for synthesis as well as functional group on the Cu NPs. Freshly prepared TBA29-T30-template copper nanoparticles (TBA29-T30Cu NPs) exhibited much stronger fluorescence at 650 nm than that of TBA29-T6Cu NPs and TBA29-T15Cu NPs. However, the fluorescence stability of TBA29-Tn−Cu NPs was very poor due to rapid oxidation of nanoparticles to TBA29-Tn−CuO/Cu2O NPs by molecular oxygen (O2) in the aqueous solution. TBA29-T6CuO/Cu2O NPs and TBA29-T15CuO/Cu2O NPs are spherical particles of about 24 nm, whereas TBA29-T30CuO/Cu2O NPs have short rod-like shapes with a diameter of about 4.2 nm and a length of about 9.2 nm. TBA29-T30−CuO/Cu2O NPs possess stronger peroxidase-like catalytic activity for the H2O2-mediated oxidation of Amplex Red (AR) to fluorescent resorufin than TBA29-T15−CuO/Cu2O NPs and TBA29-T6−CuO/Cu2O NPs. The catalytic activity of TBA29-T30CuO/Cu2O NPs was significantly suppressed in the presence of thrombin, reflecting perturbation of interfacial electron-transfer between substrates and NPs after the specific binding of thrombin with the TBA29 units on the particles’ surfaces. The H2O2/AR–TBA29-T30CuO/Cu2O NPs probe provided a limit of detection (signal–noise ratio = 3) of thrombin in serum samples of 0.5 nM. Hence, this simple, rapid, and economical sensing system shows great potential for analyses of thrombin generation in blood. The present sensing platform was further extended to detect tumor cells using Mucin1 aptamer–templated CuO/Cu2O NPs. The second part, we demonstrate a very simple method to disperse graphene in water and in situ low-temperature synthesis of MnO2 on graphene sheets’ surface using carbon dots (C-dots) through a simple chemical approach. C-dots synthesized by pyrolysis of ammonium citrate had excellent solubility in water due to its surface functional groups and dispersed graphene in water through π–π interaction and formed a stable graphene-C-dot solution (Gr/C-dot). Graphene is highly hydrophobic and cannot disperse in water which restricts its use in many synthesis reactions and making of composites for various applications. However, our C-dots can form stable dispersion of graphene in water which is a promising material for a wide variety of application in graphene based composite synthesis and catalytic experiments. The Gr/C-dot reduced MnO4− to MnOx in aqueous solution at 75 °C, depositing the MnOx on graphene’s surface to form Gr/C-dot/MnOx composite. Since the reaction was conducted at 75 °C, the C-dots were oxidized without affecting the graphene’s graphitic carbons unlike in other hydrothermal or high temperature syntheses. In order to demonstrate our approach can be applied to the modification of other carbon materials without affecting the conductivity of the electrodes, we used dipped-coating method to synthesize C-dots/MnOx onto the graphene surface of the multilayer carbon nanotube paper (multi-walled carbon nanotubes paper; MWCNTs paper). We then applied the four-point probe measurement to measure the electrical resistance and discovered that the conductivity of the MWCNTs paper was not affected after synthesis process. The as formed amorphous MnOx on GR/C-dot exhibited good capacitance properties. Gr/C-dot/MnOx composite exhibited a specific capacitance of ~480 F g–1 at a constant charge or discharge of 0.2 A g–1. Further, the composite showed excellent stability; it retained a 95% capacitance after 5000 charge-discharge cycles. Thus, our one-pot synthesis method is green, cost effective and rapid, and has great potential in synthesis of graphene based composites in aqueous medium.