Studies On Preparation, Characterization And Electrochemical Properties Of The Au NPs And Their Carbon Nanotube Hybrids

In this paper, the chitosan nanoparticles (CS NPs) and multi-walled carbon nanotube-CS NP hybrids (MWCNT-CS NPs) were synthesized by an ionotropic gelation process. These natural polymer-based CS NPs and MWCNT-CS NP hybrids were utilized as templates for preparation of gold nanoparticles (Au NPs), platinum nanoparticles (Pt NPs) and MWCNT-Au NP hybrids. The particle size, micromorphology, dispersive properties and spectral characteristics of the prepared nanomaterials were characterized by various analytical methods including atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), ultraviolet-vissible (UV-vis) spectrometry, and Fourier transform infrared (FTIR) spectrometry. The electrochemical performances of MWCNT-Au NP hybrids or MWCNT modified electrodes to oxygen electrochemical reduction reaction or guanine electrochemical oxidation were investigated in detail by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The microRNA detection by DPV using MWCNTs modified electrodes was also evaluated preliminarily. The main works are as follows:1. The CS NPs were synthesized by an ionotropic gelation process. They were utilized as templates for preparation of Au NPs or Pt NPs that obtained through reduction of HAuCl4or H2PtCl6precursor by NaBH4. The preparation conditions were optimized and the properties of the Au NPs and Pt NPs were investigated by TEM and UV-vis spectrometry. The results suggest that it can obtain Au NPs or Pt NPs with small particle size, narrow diameter distribution and high dispersibility by utilization of the CS NPs as templates, which are able to confine the growth of Au NPs or Pt NPs and prevent the accumulation among them. The particle sizes of Au NPs and Pt NPs are about2-4nm and3nm, respectively. The Au NPs have excellent dispersive property in aqeous solution and no obvious precipitates were observed in the Au NP suspension after stored at room temperature for20days. The concentrations of sodium triphosphate (TPP) and HAuCl4have significant influence on the particle size and diameter distribution of the Au NPs. Based on the same principle, the mentioned method can be used for the synthesis of other metal or alloy nanoparticles that their precursors are negatively charged.2. Based on the above results, the MWCNT-CS NP hybrids were synthesized by the similar method with that of CS NPs and ultilized as templates for preparation of MWCNT-Au NP hybrids. The micromorphology, loading mass of Au on MWCNTs and the electrochemical property of MWCNT-Au NP hybrid modified electrode to oxygen electrochemical reduction reaction in alkalescence electrolytes were investigated by various analytical methods in detail. The results suggest that using the MWCNT-CS NPs as templates, the Au NPs with small diameter and high dispersibility have been tethered onto the surface of MWCNTs. Compared with the MWCNT-Au composites that prepared through the NaBH4reduction of HAuCl4-MWCNTs aqueous suspensions or CS acetic acid solutions containing MWCNTs and HAuCl4, the obtained MWCNT-Au NP hybrids modified electrode possesses better electrocatalytic property to oxygen electrochemical reduction reaction. Under optimal conditions, the peak current density of oxygen reduction reaction at MWCNT-Au NPs/GC electrode reaches-1.31mA cm-2. The mentioned method may be used for synthesis of MWCNT-metal nanoparticle electrocatalyzers, which have potential applications in fuel cell or air cell and other electrochemistry.3. The electrochemical behaviours of guanine at GC, carboxylated MWCNTs, grapheme and MWCNT-Au NP modified GC electrodes were investigated by DPV in detail. The biosensing interface based on MWCNTs modified GC electrode was constructed for electrochemical detection of microRNA and its analytical performances were discussed preliminarily. The results demonstrate that the carboxylated MWCNTs modified GC electrode has better electrocatalytic property to electrochemical oxidation of guanine. Under the optimal conditions, the sensitivity and detection limit are1.071μA μM-1and0.01μM, respectively. The miRNA-24was detected though the change of peak current of guanine before and after the hybridization between the target miRNA and the capture probe that immobilized on the MWCNTs/GC interface.