Synthesis, Characterization And Application Of Nanoparticle Compound In Biosensors/Thermo-sensitive Interface

This paper is composed of four parts. The first part, we construct a novel electrochemical alpha-fetoprotein (AFP) immunosensor based on the multi-walled carbon nanotubes/silica nanoparticles (MWCNTs/SiO2) composites, which is obtained by the galvanostatic deposition technique. The second part, the temperature control process of the super-hydrophilic and hydrophobic is realized by grafting poly(N-isopropylacrylamide) onto the well-dispersed SiO2nanoparticles obtained by the galvanostatic deposition technique. The third part, a system of logic gates based entirely on gold nanoparticles (Au NPs) and cytosine-rich DNA strand are constructed. At last, using Au NPs as an indicator, we develop a novel "UV-vis" assay strategy for sensitive and selective detection of As (Ⅴ) in aqueous solution based on the reaction of DNA and arsenic ion.1. In this contribution, we develop a novel type of multi-walled carbon nanotubes/silica nanoparticles array (MWCNTs/SiO2) composite by the galvanostatic deposition technique. In this process, MWCNTs were mixed with ammonium fluorosilicate to form a doped precursory sol-gel solution, the electrochemically generated hydroxyl ions at negative potentials promote the hydrolysis of ammonium fluorosilicate, and the simultaneously generated hydrogen bubbles assist the formation of three-dimensional porous silica matrix, further facilitating the construction of SiO2nanoparticles (SiO2NPs) array with uniform distribution, as confirmed by scanning electron microscopy. The formation of SiO2NPs array provides a higher surface area and biocompatible microenvironment for retaining the native activity of the immobilized biomolecules. Further incorporation of MWCNTs into SiO2NPs array improves the electronic conductivity and enhances the electroactive surface area of the film, making the fabricated three-dimensional porous MWCNTs/SiO2electrode an ideal platform for further immobilization of AFP, as a model protein. This method achieves ultrasensitive detection of AFP antigen with ferricyanide as a probe. The obtained results provided a linear response range from0.1to30.0ng mL-1AFP antigen with a lower detection limit of0.018ng mL-1. This work implies that the biocompatible and controllable three-dimensional porous SiO2NPs array possessed potential applications for biosensing.2. This paper reports a facile synthesis of thermosensitive SiO2nanoparticles coated with poly(N-isopropylacrylamide)-related copolymer in ethanol solution. A functional monomer, namely3-(trimethoxysilyl)propylmethacrylate (TMSPMA) with methoxysilyl group (-SiOCH3) was copolymerized with N-isopropylacrylamide (NIPAm) to yield a thermo-sensitive copolymer, poly[N-isopropylacrylamide-co-3-(trimethoxysilyl)-propylmethacrylate]([P(NIPAm-co-TMSPM A)]). Such copolymer hence possesses the capability for the silanization of the SiO2nanoparticles. Thermo-sensitive [P(NIPAm-co-TMSPMA)] capped SiO2nanoparticles were then easily obtained by covalent polymerization in the presence of the copolymer in ethanol solution. Fourier transform infrared (FT-IR) spectra confirmed the formation of hybrid hydrogel thin films after hydrolysis of the methoxysilyl groups (-Si-O-CH3) and subsequent condensation of the silanol groups (Si-OH). The dispersed SiO2nanoparticles of electrodeposition have mean diameters around100nm. The [P(NIPAm-co-TMSPMA)] capped SiO2nanoparticles show thermo-sensitive properties. With thick grafted [P(NIPAm-co-TMSPMA)] layer, the thermo-sensitive behavior of the composite SiO2nanoparticles is reversible. The [P(NIPAm-co-TMSPMA)] capped SiO2nanoparticles also exhibit super-hydrophilic behavior. Microdomains were observed for the hydrogel thin films on ITO surface, which can be attributed to inhomogeneous network structures. The thermoresponsive swelling-deswelling behavior and the super-hydrophilic or hydrophobic properties of the hydrogel thin films were investigated as a function of temperature (15-45℃) by using a contact angle meter (CA) and UV-visible spectrophotometer (UV-vis) operated in water.3. Most of the DNA logic gates employ fluorescent or colorometric signals as their outputs, having the advantages of versatility, simplicity and simplified optical setup. In this letter, we describes a system of logic gates (YES, AND and INHIBIT) based on the T/C-rich oligonucleotides modified Au NPs for the selective analysis of Hg2+and Ag+ions using the principles of metal-ion-mediated base pairs and the pH-sensitive conformational transition of cytosine-rich DNA strand. We show that this Au NPs aggregation is driven by the formation of metal-ion-mediated base pairs formed between the T/C-rich oligonucleotides modified Au NPs using Hg2+and Ag+ions. The Au NPs aggregation happens only at slightly alkaline pH conditions (pH-8). The Au NPs aggregation is reversible by adding to the quantitative EDTA or NH4OH. The assembly and disassembly process is accompanied by distinct color changes that are clearly visible to the naked eye. This development may have applications in the controlled assembly of reversible nanostructures and/or devices.4. Arsenic is highly toxic in all of its forms found in natural groundwater. In this report, nanoprobes which could detect the low level of arsenite ions in water have been proposed. The nanoprobes are composed of single-stranded DNA (ssDNA) and Au NPs. Based on the principle that uncoiled ssDNA and folded DNA bound to arsenite ions have different propensities to adsorb on Au NPs in colloidal solution, we design a label free colorimetric assay for arsenite ions sensing based on color changes associated with Au NPs aggregation. The method is found to be effective at trace levels having a linear response at the concentration range5-2000ppb. The detection limit of the proposed method is2ppb (3σ), which can be reduced further by making some modifications to the apparatus. The method was successfully applied to the analysis of synthetic samples and field samples of water.